This week’s live Q&A was a by-request topic: retaining walls, angle of repose, and zone of influence. Specifically — how close can you build to a retaining wall before it starts putting extra load on it?

Thanks to Rob Dontis for the question. Here’s the rundown.

What a Retaining Wall Actually Does

Retaining walls hold up dirt on one side to create a flat (or flatter) area — a high side and a low side. In Queensland, who owns a retaining wall usually comes down to who it was built to benefit. That’s a whole separate conversation, especially with older walls, so we won’t get into it here.

What we will get into is the two things that decide how much load ends up on your wall: angle of repose and zone of influence.

Angle of Repose

Angle of repose is the angle at which soil naturally settles when it’s piled up under its own weight. Keep adding soil to the pile, and it keeps that same angle — it doesn’t get steeper.

This matters because it’s the soil sitting above that angle of repose line that actually loads up your retaining wall. As engineers, we treat that load a bit like a water load: it increases with depth, so it’s biggest at the bottom of the wall and smallest at the top. We model it as a triangular load.

When we design a wall, we’re looking at the total force and how it’s resisted — whether that’s a concrete slab, a deep footing, or a sleeper-and-post system with steel posts driven into the ground.

Why Drainage Matters So Much

Angle of repose isn’t fixed — it changes when soil gets wet.

Think about building a sandcastle. Sand straight out of the bucket holds its shape. Pour water on it, and it slumps. The same thing happens to the soil behind your retaining wall. Wet soil has a flatter, wider angle of repose, which means more soil ends up above that line — and more load on your wall.

That’s why drainage is such a big part of retaining wall design. We’re not just designing the wall as a structure; we’re designing it as a drain. A layer of rock or filter material behind the wall lets water escape, keeps the soil free-draining, and keeps that angle of repose (and the load on the wall) as low as possible. Skip the drainage and you’re asking the wall to carry a lot more than it needs to.

Zone of Influence — How Close Is Too Close?

This is the part Rob actually asked about.

Zone of influence covers what happens when there’s a structure, a person, or a vehicle on the high side, up on top of the wall. How close can that load be to the wall before it actually transfers into the wall?

The angle of repose gives us the answer. Anything sitting within that zone — inside the angle of repose line — is already loading the wall, so it has to be accounted for in the design. That includes people, vehicles, buildings, anything with weight. And even though that weight is pushing straight down, the way soil behaves means it translates into a horizontal load on the wall.

A simple way to picture it: if we’re using a 45° line (a 1:1 ratio, our default starting assumption for clay soils) and the wall is 1.8 m high, then anything closer than 1.8 m to the wall is inside the zone of influence and is loading the wall. Anything further away than that isn’t.

If there’s nothing currently in that zone but there’s a reasonable chance something could end up there — a car parking, someone walking, a future structure — we still design for it. You can’t always guarantee no one will ever build, drive, or walk in that space, so as structural engineers we allow for a surcharge load:

• Around 5 kPa (roughly 500 kg/m²) if vehicles could drive on the high side
• Around 2 kPa (roughly 200 kg/m²) for foot traffic only

That surcharge gets added on top of the soil load itself when we design the wall.

Can You Build on Top of a Retaining Wall?

In theory, yes — but the engineer needs to design for it. The wall, the footing, and the posts (if it’s a sleeper wall) all need to be sized to carry that extra load safely.

Got a Question for the Next Live Stream?

That covers angle of repose, zone of influence, and how close you can build to a retaining wall. If you’ve got a question you’d like answered on a future live stream, let us know — it gives us a chance to think it through properly before we roll the camera.

Get in touch with Cornell Engineers if you need a retaining wall assessed, designed, or checked before you build near one.

Video Transcript

Retaining Walls: Angle of Repose & Zone of Influence — Video Transcript

I’m Matt Cornell from Cornell Engineers. Welcome to your Saturday morning. Today we’re doing a by-request — a quick chat about retaining walls, zone of influence, and how close you can build to a retaining wall. We’ve actually gone back to the old style because you’re going to need to see my hands — the overhead camera. So welcome aboard. Let’s talk about retaining walls.

Retaining walls, as we all probably know, are used to hold up the dirt on one side to create a flat side, or a flatter side, on one side — a high side and a low side. In Queensland, the ownership of a retaining wall comes down to who the retaining wall was built to benefit. We’re not getting into that so much today, because that gets very complicated, especially when you’re talking about old retaining walls.

But let’s talk about zone of influence and how close — the questions that Rob Dontis actually raised for us were: retaining wall angle of repose, and zone of influence — how close can you build to a retaining wall? So let’s cut to the overhead and have a little chat about this.

Okay, so retaining walls, like we said, are typically walls. Sometimes they’re vertical, sometimes they’re less vertical, or built into the slope a little bit. But in this case, we’ll show the lower ground on this side, we’ll show the high ground on this side, and this here is our retaining wall. It’s holding the dirt, stopping it flowing down onto the low side.

So when we’re talking about angle of repose — I’m going to need another piece of paper already — angle of repose is the angle you get when soil gets dumped in a pile and it sort of settles down under its own weight. The more you build it up, the more you build it up, it still keeps that same shape.

That’s important to us because it’s the soil that lands on top of that angle of repose that actually helps put load on our retaining wall. So if our retaining wall was built here, it’s this soil above that line that is actually putting a horizontal force onto our retaining wall.

As engineers, we look at this force from the soil in two ways. It’s sort of like a hydraulic load, like a water load — the higher the wall gets, the bigger the load gets at the bottom, and the load actually gets smaller towards the top. We show it as a triangular load, as engineers.

When we’re designing a retaining wall, we’re more interested in the overall forces on the retaining wall and how it’s resisted — whether there’s a concrete slab underneath, or a deep footing built into the ground. That was the sleeper retaining wall with a deep footing built into the ground, or the concrete slab, which is what we’d normally use for a concrete masonry retaining wall. There’s also timber retaining walls, which are a bit like the sleeper retaining wall with the deep footing built into the ground. But this wall is essentially just holding back that soil that is above that angle of repose.

The angle of repose changes when the soil gets wet. So remember the last time you went to the beach and you built a sandcastle. Sand sitting on the beach, straight out of the bucket, the sand stays up nice and straight. As soon as you pour some water on it, it slumps.

So imagine you did that to the soil behind your retaining wall — you poured water in behind the retaining wall. The water does the same thing to the soil behind the retaining wall, unless it’s rock, as it does to the sand on the beach. It makes it slump.

So when we talk about retaining walls, we talk a lot about drainage. We talk about the force of the soil on the retaining wall that we’re designing as a structure, but we’re also talking about it as a drain. We don’t want water building up behind the retaining wall, because that extra water — apart from the fact that it can also put load on the retaining wall itself — also makes the soil slump a lot quicker, and puts a lot more load on the retaining wall.

If we had the choice, we’re going to design a retaining wall to be as economical as possible. So we include drainage — a layer of rocks or filter material that lets the water out of the soil, so that the soil is free-draining and the angle of repose stays nice and vertical. Angle of repose for wet soil would be much flatter, and there’s a lot more weight being applied to the retaining wall as a result. So that’s angle of repose.

Zone of influence isn’t really covered there. Let’s go back to our nice, neat retaining wall diagram. Our zone of influence is more about when we have a structure, or someone standing on top of the wall, or someone driving on top of the wall on the high side of the wall. How close can they be to that wall without it putting load on the wall? Or alternatively, if it’s close to the wall, how much of that load actually gets transmitted into the wall?

It has to be designed by the engineer, with the footing and the strength of the wall itself, the strength of the steel posts. If it’s a concrete sleeper retaining wall with steel posts and concrete sleepers between it, how much of that load has to be covered by the retaining wall. Ideally, the further you put the load away, the better.

The angle of repose tells us that anything within that line of soil — where that soil on top of the angle of repose is already putting load onto the retaining wall — has to be designed for it. That extra weight from people, cars, and buildings on top of the retaining wall also applies a load to that soil. It might look like they’d just be pushing straight down, but because of the way soil behaves, that load also translates into a horizontal load on our retaining wall.

So the answer to “how far away does something have to be before it no longer applies load onto the retaining wall” becomes a little bit simpler once we understand this zone of influence line. Say it’s a 45-degree line — a one-in-one line — and the wall is 1.8 m high. That line of soil that’s affected, that puts load onto the retaining wall, is obviously 1.8 m out. So if you’ve got a 1.8 m high retaining wall and you’re closer than 1.8 m with your building, your vehicles, or your big heavy people walking across the top of the retaining wall, those loads are being resisted by the retaining wall. If you’re further away than that line, they’re not — assuming a 45-degree line, which is our basic starting point if we don’t have any other information. We’ll typically assume it’s a clay soil, and we’ll assume about a 45-degree line.

If you’ve got nothing in that zone right now, we’re still going to design your retaining wall for that surcharge load, because you can’t necessarily stop someone building there, or driving there, or someone walking across the top. We’re going to have to allow for it in our design as structural engineers.

So we allow maybe 5 kPa — 500 kg a square metre — if someone can drive on that high side of the wall. A little bit less if it’s only a footpath — maybe 2 kPa, 200 kg a square metre, which is still a fair bit. And that’s the extra load, on top of the weight of the soil, being applied to the design of the retaining wall.

So, I think we’ve just about covered all the questions we had from Rob Dontis. Retaining wall angle of repose — we’ve covered it. Zone of influence — we’ve covered it. And how close can you build to a retaining wall — we’ve covered that too. In theory, you can build on top of a retaining wall, don’t forget — it just means the engineer has to take that into account when they do their design.

I’m Cornell from Cornell Engineers. I hope this has been useful. Stay tuned, we’ll have some more live streams every now and then — you know what, there’s a lot less editing involved in setting up a couple of cameras and having a chat to you live than there is when I record with multiple cameras and put it all together. This is way easier for me.

So, if you like this, and you’ve got a couple of questions you’d like me to answer in the next live stream or in future live streams, let me know. That’ll give me a chance to have a think about what we’re going to say — we’ll roll the camera and I’ll answer your questions.

I’m Cornell from Cornell Engineers in Queensland, Australia. Hope you have a good weekend. I’ll catch you later.

Transcript
Here is the timestamped transcript, broken down into chapters based on the discussion topics.

Chapter 1: Introduction & Technical Difficulties (00:00 – 01:50)

Matt: G’day, this is Matt Cornell, and I really apologise. We’ve just started our video, and I got 14 minutes in to discover that you couldn’t hear a thing I was saying, and really sorry about that. So, I think we might have another crack. We’re streaming again. It’s a different link, so apologies for that false start, and hopefully, this will work this time.

Matt: So sorry, Sayla! We were doing such a good job, too, but now that we’ve—we were on a roll. Now that we’re really experienced with this, we’ll have another go. So we do have a series of questions. We haven’t received any comments or questions yet, so we’ll go through the questions that we had generated earlier. They’re in that other live link, and I’ll add them to the description of this video, too, after we’ve finished.

Matt: We’ll work through them. It’s about a one-hour cast. Later on, I’ll put the questions in or the time stamps in for the questions, but for now, without further ado, since we’ve had some good practice with the other one without sound, we will cut straight into answering the questions. My name is Matt Cornell, I’m from Cornell Engineers here in Brisbane, Australia, and this is Sayla.

Sayla: Hi!

Matt: She’s a structural engineer, and um, this is actually her last day before she takes some maternity leave, so congratulations, Sayla, we’re very pleased for you. Thanks very much for joining us. I’ll hand over to you, Sayla, and we’ll go start with question one.

Chapter 2: Wall Cracks: What’s Serious? (01:50 – 04:20)

Sayla: Right, so we’ve got 35 questions in total. The first one pertains mostly to worried homeowners. So, these are questions that we get a lot over the phone, usually with a nervous tone behind them. So, first question is: “How do I know if a crack in my wall is serious?”

Sayla: Most of the cracks that we see in homes—specifically wall cracks—are usually around openings such as windows or doors, or along trimmings. So, once again, windows and doors, but also along the tops and bottoms of walls, so maybe where a corner of a corner would come together. These types of cracks are not totally uncommon. How do you know if it’s serious?

Sayla: So, a couple of things: First, we like to refer to Australian Standards, which tell us a lot about if a—there’s a standard actually in AS 2870 that talks a lot about minimum widths of cracks that somebody might look at to understand once they want to take it to the next level. So, 5 millimetres—I’ve understood it to be 5 millimetres—is the maximum width of a crack across the width of a crack that you can measure in a wall, such as plasterboards or finishings, to understand if it’s something that we want to address immediately. So, after 5 millimetres immediately. If it’s less than 5 millimetres, it comes a little bit more down to: Is the crack stabilised, or is it continuing to move?

Sayla: So, you can do this by taking a good record of what the cracks look like to date. So, maybe you step back, take a nice photo, maybe throw a tape measure in there to understand the length and the width of the crack to date. And then you come back and visit it, maybe six months or a year in time, after you’ve seen a couple of seasons, which homes tend to react to. So, humidity, changes in moisture outside, these things all can affect cracks. So, take another visit in six months or a year. If you see a lot of progression in a crack, then maybe it’s time to get a professional, such as a structural engineer, involved.

Matt: The 5mm limit is a Queensland thing, it also comes from Victoria. The Queensland government QBCC only start getting serious when a crack’s wider than 5 millimetres in general, or there’s a series of cracks maybe slightly smaller, but a series of 5 millimetric cracks throughout the home or in a vicinity. And that’s when someone starts—the government, for example, for a new home less than six and a half years—starts getting serious about investigating the damage. If it’s an older home, and the cracks have been there for 20 years, that’s a totally different sort of scenario to something that’s occurred and opened up in the last three to six months. A live crack is something that we’re more likely to investigate or need to investigate than something that cracked 20 years ago, stayed like that until now, and hasn’t changed. Pretty much, if it hasn’t changed at all in the last 20 years, go ahead and get it repaired. Question two.

Chapter 3: Seasonal Movement & Slab Heave (04:20 – 09:30)

Sayla: Number two: “My house has cracks that open in the summer and close after rain. Is that normal?” So, Southeast Queensland, we see a lot of—well, specifically a lot of clay, but other reactive soils that are in the ground that we’re trying to build our homes on and around. These soils react highly to moisture conditions. So, if you have seasonal changes—wet season, dry season—you might see your home reflect that.

Sayla: So, if you’re seeing cracks that open in the summer, it might mean that you’re seeing some swelling in foundational soils due to moisture, and maybe they’re closing as they shrink in the dry seasons. And this is very common, those forces are very strong, they’re strong enough to move your house up and down. Usually, when it comes to damage of that nature, we want to make sure that—I mean, first of all, that your foundational soil around your home and underneath your home is as consistently dry as possible. And there’s lots of sources for water, you know, there’s overland flow during rains, there’s plumbing faults underneath your slab. Maybe you get a plumber involved, run a camera through there, make sure nothing’s damaged. There’s downpipes around your home coming from the roof, make sure that nothing’s cracked or leaking, especially down at the bottom.

Sayla: Another big one is garden beds that run along the side of your home. So, if you have an irrigation system or something that’s designed to add moisture or hold moisture against your footings, we usually recommend to try and remove them or add other precautions to try and keep your foundations dry. So, those are pretty common for seasonal movements and cracks. Is there anything I’m missing?

Matt: No, I think that’s pretty much it. So, say they’re small cracks—well, if they’re seasonal cracks opening and closing, and you aren’t able to manage that by addressing moisture changes or trying to stabilise moisture changes, we do have some tricks up our sleeves for improving the ability of a building to accommodate movement without unsightly cracks. And that generally involves control joints. What people know as brick control joints, or joints in the plasterboard, which are plasterboard control joints. They allow a little bit more flexibility in your home to move unevenly due to foundation movement, summer and winter crack movement, but without causing unsightly cracks. It’s hidden in the control joint, or it’s hidden in the plasterboard control joint. So, that’s your backup plan if the seasonal movement is recurring, and you’ve repaired it, and it keeps coming back. Then there are some plans; there are some ways an engineer can specify control joints to help hide that and make it less obvious, less aesthetic.

Sayla: Where are we, number five? “What is slab heave and is my house at risk?” So, heave, being the raising of the slab, once again usually occurs due to swelling in the foundational soil. So, if you’ve got an upward movement happening in your foundations due to moisture additions, which is causing that swelling, then you might see similar cracks to what we discussed before. So, slab heave damage would look like cracks around, specifically at the corners of openings. If you see vertical cracks at the edge of your foundations, then slab heave is probably considered to be getting maybe a little bit more worrisome. So, beyond that point, then we would probably step in and see what we can do for you.

Matt: Just a reminder that slab heave isn’t always the ground going up, even though it sounds like it is. It could be it’s differential. So, if some part of the house is going down and some’s going up, and some is staying the same, it still looks like one part’s going up relative to the other part. So, keep that in mind.

As engineers, when we go to investigate that, we’re looking for reasons the house is moving, not just why is it lifting. We’re looking for subsidence, uncontrolled fill that hasn’t been compacted properly, piers that haven’t been maybe extended to deep enough soil if it was fill, and the designer was already aware there was soft soil on site. Slope stability: there’s a series of reasons and things that we look for and rule out one by one that could be making the house go down.

Matt: And also, what things could be making the house go up—the other things that we spoke about already, the dog holes beside the house where water ponds next to the footings, obviously a bad thing. Gardens beside the house, not great. Dripping taps, broken pipes, all those sort of things result in slabs going up. And one of our tools is a floor level.

There are videos on our YouTube channel on how we take levels, and how we turn that into a contour plan, and then how we interpret that for addressing specifically slab heave or uneven house movement, and then using that interpretation, what you can do to sort of solve those problems.

Chapter 4: New Construction Cracking (09:30 – 13:30)

Sayla: Where are we, number three. So, also another common question: “Is it normal for a new house to develop small cracks?” So, cracks due to movement that occur during construction or immediately after construction usually have to do with just the weight of a new structure settling into its bones and into its foundation. So, if you’ve got a little bit of movement that you see sort of inconsistently across your home right after a build, specifically up until I think, the five-year point would probably be a good rule of thumb, then that might just be temporary settlement that will stabilise over time, and hopefully, you can sleep at night knowing that will occur.

Sayla: But once you get to that five-year point, maybe beyond that, it might be something a little bit more serious that you want to get an engineer involved. So, if your soils are settling a little bit, usually that has to do with compaction of the soil, how well your builder did putting the site together before he built the foundations, and the design of the footings themselves. So, did your engineer take into account what types of soils are on the lot? Do the footings reach good bearing soil so that that’ll help minimise that downward settlement due to the gravity, the weight of the structure? Yeah, those are the sorts of things we’d like to look at if we see a lot of movement right after construction.

Matt: Don’t forget a lot of builders in that defect liability period, the 12 months after construction, are generally happy to come back and repair a few minor cracks, things that they consider minor, small and minor. They will happily send back a plasterer or a painter because they’re aware these things happen. They’re more than willing to—if you go around with some red dots and mark out some of the damage—some of them, yeah, maybe they won’t; some of them might be, if the damage is too big, then they’re going to refer that to their engineer to have a look at. But the minor stuff, yeah, you might get away with the builder coming back at about the 12-month period, repairing that sort of stuff. If it comes back, then yeah, maybe we’ve got to have a chat.

Sayla: Number four: “My builder says cracking is normal movement. How do I know if they’re right?” So, if you’ve got a good builder who’s done his due diligence and made sure that he’s put together a good product for you, and you know, throughout the construction phase you’ve got other professionals involved to make sure that it’s inspected thoroughly and is built in accordance with the drawings and the design that’s in place for the home, then you know that if it’s been signed off and certified, these things have been checked. Any cracks that you might be seeing might just be that settlement that we were talking about in question three.

Sayla: If we’re talking about a home that’s older—you know, older than that five-year period certainly, but beyond that—then a builder could probably comment quite a lot about what sorts of damage he sees and what’s serious or what isn’t serious, but most good builders will welcome a second opinion. So, if you just have a gut feel that maybe it’s a little more serious and you want to get a second opinion, a structural engineer is your next best call.

Matt: I haven’t got anything to add to that. That’s pretty good.

Chapter 5: Drainage & Foundation Issues (13:30 – 18:20)

Sayla: Number six kind of runs along the same theme. What causes footings to move or settle? So, this is kind of wrapping up everything we’ve talked about in the last five questions, but when you’ve got movement in your footings, there are usually three major things that can cause soil to shift or foundational soils to shift. One was the settlement that occurs immediately after construction, one is the swell and shrink that we’ve talked a little bit about when you add or remove moisture from soil, and the third one is erosion.

Sayla: So, if your footings are being quite literally undermined by soil eroding away, that’s usually storm-related, well that’s when we often see it, is when you see that overland flow, maybe it cuts up against or underneath your footings, then you’ll see erosion, which can—of course, if the footings have nothing to sit on, then they might move.

Matt touched a little bit there on some of the contour plans that lots of engineers, us included, often provide, so we do that by walking around and using a gas level to measure different elevations throughout your slab. When we do that, it’s really nice to have a point-in-time record about how your foundations are doing in one season, maybe retaking the levels and comparing it to another contour plan that we do in another season.

So, that kind of ties together everything that we’ve talked about today. If you suspect that there’s movement or settlement in your footings, we can record the current existing elevations, but we want to make sure that they’re still moving or maybe they’re settled, and that’s how we do that.

We take point-in-time records and then we come back and we do another set of plans at a different season or further on down the road and see if there’s changes, and then we can understand where is moving, how much is moving compared to other areas in the home, and that might help us understand why it’s happening.

Matt: So, that chapter was all about the worried homeowner; we’ve got those six questions under control. Moving on to foundation and drainage, which is another subject that we cover quite a lot on our website and on our YouTube.

Drainage on sloping sites is one of our popular videos, obviously. So, we’ve got a few questions here about sloping blocks and water, and we’ll start with question seven: “We’re on a sloping block and water is getting in. Is this a structural problem or a drainage problem?” Sayla!

Sayla: Well, if you’re on a sloping block, the first thing you want to understand is where the water is coming from. So, if you have—maybe there’s a home further up the block from you that might be directing overland flow into your allotment, that’s quite common for sloping blocks. The other thing is, sometimes with sloping blocks we have water retained around the foundations of our home, sometimes, for example, if you cut and build.

So, if your home is sitting with a retaining wall supporting soil up against your exterior walls, those are common areas where if we’re going to see structural damage or drainage issues that involve entry into your home, that it can get a little bit tricky, and it’s important that they’re constructed correctly.

Sayla: So, back to the question there where we were saying, is it a structural problem or a drainage problem? So, I guess the answer is it could be both. So, if you have a structural retaining wall that is retaining soil outside of your home, obviously it wants to be—it has to be built such that water can’t get in, so the builder will construct the wall, it’ll have waterproof layers, but then there should be a drainage layer behind it that helps direct any moisture that’s maybe underground water or overland flow around your home instead of pooling up against the face of the retaining wall. So, I suppose that’s—

Matt: Yeah, I guess the answer, my two cents is, that it’s both. Water landing or heading towards your home can cause structural issues, and if it’s caused by water, then it should be solved as a drainage issue first. Then, if it can be, the structure can be upgraded or changed later, but it’s going to be cheaper to try and solve it as a drainage issue rather than a structural problem first.

Improve your drainage, find where the water’s coming from, solve those issues, get the water around the house instead of through it, and then we can talk about solving the structural issues if there are any issues left in six months after the ground around your home dries out.

Chapter 6: Soil Classifications & Slab Types (18:20 – 23:00)

Sayla: Right. Number eight, more soil questions. So, this one is: “My soil test said H2—or Class H2, as they say in Australia—what does that mean for my house?” So, H2, your soil tester will give a site classification that talks about how reactive your soils are.

So, we’ve kind of beat this drum a little bit quite a bit during this conversation, we’ve talked about how moisture can affect your foundations, but specifically what type of soil is in the ground and what your house is sitting on, and how reactive it is, is going to talk about how much movement you really need to build your foundations to withstand.

So, you can have slightly reactive soils, you can have moderately reactive soils, or you can have highly reactive, and that’s where that H for H2 comes in. So, if you have H2 soils, that means you have highly reactive soils on your lot, and your footings should be built in accordance with that.

Matt: There’s also a H1. In the old days, previous versions of the Australian Standard AS 2870, there was only a H class site. The latest and maybe the second latest versions of the Australian Standard have separated that high and low region of the highly reactive soils out.

I guess they were getting too many houses being over-designed, too strong, when it only needed to be a little bit stronger than an M class, a moderately reactive soil. So, they’ve divvied that up, made H1 and H2. H2, therefore, means that you’re on the higher end of the H class soil, a little bit more care and attention required for site drainage, a little bit more strength and stiffness required in your footing and slab system.

Sayla: Right. Number nine: “What’s the difference between a waffle slab and a raft slab, and does it matter?” So, waffle slabs—waffle slabs are typically a little bit cheaper to construct, but they do have their demons. So, with a waffle slab, you’re looking at, you know, like a basically a big block that’s filled in with filler blocks, so usually styrofoam or something of that nature, that will give you that sort of classic waffle look. So, it’ll look like strips with your concrete slab poured on top of it. This is usually sits quite high on the ground.

Sayla: I think waffle slabs do sometimes inlet into the ground a little bit, not in the way though that a raft slab would. So, a raft slab is one where we’re actually cutting down into the earth to a depth specified by your engineer to get those strip footings which act as sort of concrete beams, and then your slab—your slab is cast over top of that. So, in this case, your slab would be sitting on soil in between the beams instead of that styrofoam or similar filler. So, that’s the main difference.

Matt: That’s great. On our YouTube, we do have some videos on watching a waffle slab come together, and inspection on a waffle slab inspection where I videoed it and told you what we were looking for, so don’t forget to check that out. We, Cornell Engineers, we don’t design waffle slabs. It’s a long-standing agreement that we’ve had with waffle slabs that we don’t interact with them. We’ll inspect them at construction stage if someone else has designed them, if we need to, but generally, we prefer raft slabs, we think they’re—they might be old school, but in my opinion, anyway, they’re a little bit stronger. I can feel a lot more confidence specifying raft slabs than a waffle slab, it’s just a personal preference. There’s plenty of engineers out there that are happy to do waffle slabs and they’re more than competent and able to certify them, that’s up to them, that’s good.

Chapter 7: Retaining Walls & Timber Rot (23:00 – 28:10)

Sayla: Number ten: “Can retaining walls fail, and how would I know?” So, different types of retaining walls that we see commonly around here is concrete masonry retaining walls, which are made out of cinder blocks with reinforcement inside them. Those are probably the strongest option. There’s also sleeper retaining walls, so that would look like either concrete or timber. Concrete is supported by steel posts intermittently filled with concrete sleepers, or timber posts with timber sleepers.

Sayla: Most of the failures that I’ve seen in my short time has been pertaining to timber sleeper retaining walls, which we see a lot around here, especially in Brisbane. These timber walls, they don’t usually stand too high, usually maybe, you know, 1 to 1.2 metres, sometimes taller, but they’re often used in garden beds or trying to just landscaping elements around your home. And, of course, you might guess that the main issue with them is rot and degradation due to moisture. Specifically, when you see these walls fail, it’s because the posts, or the bottom of the posts where it meets the soil, is usually where you see the damage, and once those posts fail, then the weight of the soil and the water and everything behind it tends to just push the wall forward. In the other types of walls, you know, like if you’ve got a concrete masonry wall that’s on the brink of failure, that would start with warning signs such as cracks—often step cracks, probably between the blocks or vertical cracks. You might see them in the foundations, though those might not be exposed, and the weakest point of the wall is right at the base. So, if you’re going to see something fail, you might see it deflect forward or lean sort of away from the soil face, those are sort of the warning signs that something needs to be done.

Matt: Yeah, as far as investigating, how would you know if the retaining wall is in danger of failing? For timber, you can probe it with a screwdriver. If you can stick a screwdriver all the way through where it should be solid timber, that’s a good sign that the timber’s degraded. It’s time to speak to, if it’s less than a metre, a landscape gardener, or a structural engineer if you need a report on it. They also turn up—the timber retaining walls were used a lot between, along boundary lines in subdivisions, so a lot of the older developments have timber retaining walls on the boundary. We’re investigating a few at the moment and commenting on them. The timber rot, yes, occurs down where the timber’s always wet.

Matt: Timber these days can be specified to be treated for in-ground conditions, it’s a lot different to the timber that might have been used 20 or 30 years ago where it was good solid timber, but it wouldn’t necessarily have been treated for protection against moisture being present against the timber all the time. So, timber retaining walls, even concrete sleeper retaining walls, have a timeline, an end-of-life period, they are different depending on how the wall’s been built, sooner or later, yeah, walls will degrade, and even the steel posts that get buried in the ground, eventually they’re going to corrode and start to get towards end of life.

Matt: So, the trouble is for a lot of these retaining walls, the damage is against the earth on the side where you can’t see it, so it is tricky. That’s why we probe timber, that’s why you might even probe steel, because you need to get into the area where you can’t necessarily see. So, give it a get a skinny screwdriver and go around and try poking it into the timber, and if it disappears, you need to have a chat to a builder or a landscape gardener for replacement, or a structural engineer if it needs a report.

Chapter 8: Older Homes & Structural Risks (28:10 – 32:40)

Sayla: Number eleven: “Do older Queenslanders have particular structural risks?” You know what, these homes are usually pretty well built and have been standing for a long time. They’re usually built using good old hardwood, and often you see them on stumps, so you’ll see them raised, and and that’s obviously helpful for overland flow or some of the drainage issues that we’ve talked about earlier today.

Sayla: Particular structural risks, well, because they are on stumps, one of the big issues that we see with a lot of these old homes is those stumps are often concrete stumps that you’ll see—maybe get infected with a version of concrete cancer or spalling or corrosion of the reinforcement that’s within the stumps. This is really easy to spot underneath your home where you may have storage or you park your car, these stumps are easily visible, so that’s the main issue. Also, because the structure of course is sitting on these stumps that are well-spaced out, if you have one, you know, maybe settle a little bit or raise a little bit, the height differences in your floor might be a little bit obvious. The one thing with these old Queenslanders though is they don’t often have plasterboard walls, we see a lot when we come into them, they’ll have these really forgiving slat walls that allow for a little bit of movement without seeing obvious damage, and nobody wants to look at cracks in their walls, so perhaps they have a little breathing room in that particular area.

Matt: Right up to the minute where you start renovating one of these older Queenslanders, pull all those beautiful slat walls out, make the bathroom bigger, build an ensuite or whatever, and the builder comes in and builds all new plasterboard walls. The risk then is that plasterboard walls are fairly inflexible, intolerant to movement compared to the old style walls. You’ve got a footing system that does move around season to season, and you’ve got an increased risk of things happening to those brand new plasterboard walls. Once again, we’ve got a video about that: “Old Houses Move,” and it happens. You need to be aware if you’re buying an old home or renovating an older home and you’re turning all those flexible walls into inflexible walls, there’s an increased risk that you’re going to get a little bit of movement and cracking in them. It doesn’t necessarily mean the house is falling down or the roof’s falling down, but it is something to be aware of, there’s an increased risk of cracking.

Chapter 9: Renovation vs. Demolition Decisions (32:40 – end)

Sayla: Moving on to a new section here: Buying and Renovating. “What should I look at before buying an older house?” So, older homes, I mean, we’ve got a lot of variations in types of construction that you can come across in older homes. A lot of the time you’ll see an older home that maybe has had some work done to it, so if you want to understand how strong your home is, maybe the first step is: Are you looking at a house that has been maybe renovated or maintained and kept up to date with current standards, or are you looking at a home that’s just sort of been sitting since the day it was built and hasn’t been touched?

Sayla: So, things—I mean, obvious signs- is there obvious cracks in the walls or maybe you see differentiation in the floor, you know, like if there’s a big slope in the floor in the kitchen, you know, what’s going on with that? Is there maybe issues with the foundations, or is it something we need to address, or is it something that’s been there for 20 years, like we’ve talked about earlier today? Other things to look at: If you do have additions added onto the home, it’s nice to know if they’ve been done correctly, so maybe you—

Matt: Are they approved?

Sayla: Yeah, are they approved? And you can obtain all those, especially if they’re recent, those kinds of documents and approvals from the council. And usually, there’s a building and pest involved, that’s a little outside of our scope, but—

Matt: It’s a great place to start, certainly. Structural engineers are really good at solving problems that have already been identified, but for finding the problems in the first place, even my wife and I will use a building and pest inspector to go through a home that we’re considering purchasing because they are experienced, they know what sort of things happen, they’re aware of old-style houses. The reports come with a lot of disclaimers, but the people doing the reports, they’re worth a chat, pull them aside on-site while they’re doing the inspection, ask their opinion, they can tell you a lot more in person than they’re allowed to write down, and um, they’ll point out the things that you might need to be concerned about or you might need further investigation about.

Sayla: On that note: “Do renovations need engineering sign-off?” So, this is usually where your certifier comes in. Usually, they require—especially for major renovations, but even just as something as small as a wall removal—you get it permitted or maybe you don’t, but if you have a certifier involved, they’re going to ask that you have an engineer take a look and sign it off. So, what does that look like? You know, if it’s something as small as a wall removal, maybe we issue just like a detail or a letter or something sort of semi-official that we can—you can point out and say, “Yes, I’ve had an engineer take a look at this, and I’ve done my due diligence, and I’m not affecting the structure as a whole.” For major renovations, of course, obviously, you usually need to have an architect involved or a designer, that’s the first step. The second step is a structural engineer, which can certify the structure, and then your builder has what he needs to do the job in accordance with current standards.

Matt: So, minor stuff that—it also depends on the age of the home. So, an older home, a lot of those internal walls that you’re thinking about removing, opening up between the kitchen and the lounge room, for example, good chance that wall’s load-bearing, it’s carrying part of the roof load, and an engineer is going to specify a roof beam to carry that load to the adjacent walls so that you can do it. It also means that you either get used to having a roof beam there instead of a wall, or you pay a little bit of a surcharge to have that roof beam hidden up in the roof space. If it’s a newer home and it’s an internal wall relocation, if the wall’s a bracing wall, which could be a plywood bracing wall or have strap bracing, then if that bracing wall’s being removed, it also—the bracing needs to be reinstated somewhere else in the house, in the vicinity, in the same line as the bracing wall. So, again, that’s a structural engineer gets involved in that sort of thing.

Matt: So, a lot of the time, we get questions: can we help, can we price, can we have a look at a house, can we tell you if you need engineering for the renovation you’re considering? We are the sort of person to ask, the structural engineer’s the right sort of person to ask that, and also a decent builder if he’s got a set of plans from when the house was built, should be able to tell you if it’s going to affect it. A structural engineer will tell you how to solve it if it’s going to affect the structure, the bracing, or the load-carrying—the things that are holding up and holding down the roof or the floor above.

Sayla: Number sixteen: “What questions should I ask before hiring a builder?” Okay, well, if you’re hiring a builder that’s going to be doing a renovation on your home, obviously you want to make sure that they’ve done—I mean, that they’re certified builders, but beyond that, is he willing to do the work properly, or is he maybe interested in trying to get the job done quickly? But if you have a builder that’s following good plans that’s either provided to you through him or just independently through yourself, then they should have all the tools that they need to do a good job. So, I mean—

Matt: Yeah, that’s fine. Find out about their track record. Speak to people that they’ve built homes for before. Have a look at the Facebook groups, especially some of the larger builders in Australia have pages—Facebook pages dedicated to talking about the quality of workmanship that those builders are producing for them. Find those pages on Facebook and either ask a question or do some reading for yourself.

Matt: Speak to the builder, have some of the answers in your mind already. The research that—the information that is available on YouTube and on websites, and even on artificial intelligence these days, there’s enough information out there that you should have a good idea of what the answers are before you ask them. Ask the builders those questions, see what they say. Be specific: When do inspections get carried out? Who does the inspections? Have an idea of what the answer should be for your area when you ask them, and don’t tell them that you already think you know the answer, and see how they go. See if the information they’re giving you when you ask those questions is logical, if it’s believable, and then verify it later if you have to. Write it down, find out more information so that you can tell whether or not the answer that you got is a good answer or not, and shop around a little bit. Don’t jump into bed with the first builder that says they can build your dream home for half the price that anyone else can, ask the questions, shop around a little bit, it’s worthwhile.

Matt: Insurance and disputes… Number seventeen: “How do storms and hail actually damage a roof structure?” This comes up a lot in our area, I mean, across eastern Australia, I’m sure, but in our area, we see it a lot, you know, just after Christmas, you get this influx of insurance claims that come in, and hail specifically…

Sayla: Hail specifically, hail is a bit of a beast, it can damage the sheathing on top of, you know, like if you’ve got a metal roof, you see quite a bit of hail damage in that sort of nature, and that’s—the problem is that triggers a bit of a trickle-down effect. If you replace, I think it’s more than 20% of your roof sheathing, then suddenly you have to engage a structural engineer and make sure that your roof structure is up to current standards. So, that usually just looks like minor improvements, it usually looks like us upgrading hardware and connections in your roof framing just to make sure that it’s tied down properly to the walls around it, and the independent elements that are in there are all tied together properly. So, that’s what that usually looks like. The other part of this question was storms and hail, so we see a lot of big heavy wind events. When you have wind events on a structure, it behaves in all sorts of ways. If it has the appropriate bracing, then laterally it should be—it should be able to withstand a storm in the area unless it’s beyond what we design for, but the other big one is uplift. So, your home, especially your roof, is going to have outward and inward pressures that occur due to these wind events, and a home that’s been designed for that properly, and in accordance with Australian Standards, should be able to withstand that, but how do they actually damage it? It’s they move it beyond what it’s been designed to do, is the answer to that question.

Matt: So, damage, structural damage is different to the aesthetic damage. A home might move around too much, and there’s cracking in the plasterboard, which is still an insurable event from the storm. It’s still going to maybe result in an insurance claim because we’re talking about insurance now, result in an insurance claim, and generally the plasterboard will get replaced and maybe the home will get stiffened up a little bit at that time. The damage that I think the question that engineers more often look at: Yeah, the roof, part of the roof gets lifted or blown away, or fully translates, in which case the damage looks like there’s parts missing, or there’s holes in the ceiling, or there’s holes in the roof and water’s come in as well as part of the damage—the framing’s damaged, broken, cracked, whatever. Hail damage can look like holes in the roof, hail has damaged roof tiles before, it can go straight through the skylights and non-structural elements of your home. All that comes together when a loss adjuster and a building consultant go through and look at your home. Structural engineers, in particular, get involved when it’s definitely structural damage, the rafters slash or trusses have been affected by the storm or the hail event, and sometimes the storm damage isn’t just from wind, it’s a tree gets knocked blown over and lands on your house. And that obviously causes damage, too, it’s still storm damage, and a structural engineer is going to probably get involved then to help assess the extent of the damage, how much of the building needs to be repaired, and how to do it so the builder’s got a good idea and has a set of drawings or at least some notes on how to reinstate or repair the and remediate the damage.

Sayla: Number eighteen: “How soon after the storm should I get an inspection?” Well, maybe I’ll preface that question just by saying if you—it might make sense to always have a good record of the condition of your home, so maybe if you do a lap before an upcoming storm it might help you understand areas that—you know, after a storm comes through and you see a crack that maybe you didn’t see before, well, are you seeing a crack because a storm has damaged it, or are you seeing a crack because you’re looking for something that maybe you didn’t look for before? Take photos, take videos, absolutely. If you can prove it, the whole process is going to be a lot easier for you to get through to the end with a little bit of help, especially from the insurance side of things. How soon after the storm? Immediately, if you see immediate damage.

Matt: If you can, everyone’s going to be affected by that storm, it’s tough to get consultants and builders to turn up after a storm, a serious storm affects a lot of buildings. Take photos, if you’ve taken the photos beforehand, then yes, you’re very lucky and very wise. If it’s just a set of photos after the storm, get in there, take some photos, if you can, don’t go into a building if it’s unsafe, fly a drone, poke a camera through the window or on a extendable pole or something. Or just stay out of the structure and take photos from the outside, but take some photos, add them to your file, don’t lose them, make sure they’re time-stamped, which they all are these days, digital photos, and and then lodge that claim and pass that information—it might be relevant to the loss adjuster or the insurance company, and if it’s not, you’ve still got it on record, it’s a good thing to have.

Sayla: Which kind of leads to the next question, which is: “How do you determine if damage was pre-existing versus storm-caused?” So, I mean, if you look for it beforehand, then obviously you’ve got your ducks in a row and you know what the condition of your home is before the storm. Most of us don’t think to do that, though. So, how do you determine if it was pre-existing versus storm-caused? Sometimes, I mean, if we get involved with a house that’s got some damage to it and we’re a little bit unclear, things like pictures from your building and pest inspection or maybe realestate.com can be really enlightening. Beyond that—

Matt: Party photos! Everyone is sitting around the house, the kids standing in front of the back wall. Any of those photos, if you’ve got them that show the condition that the wall was in in good nick prior to the insured event, and and can show that now it’s damaged, that helps us a lot. It doesn’t matter if there’s kids in the way, we’ll take those photos, accept them as gospel, and that forms part of our report, it makes it a lot easier. Realestate.com, a lot of people don’t realise, or Street View, if that damage is visible from the street, and Google Street View’s run their camera past there, and we can show—use that to show that there was no damage before the event, there’s damage after the event, then you’ve got a—it’s an easy one for us, we can say definitely show that the damage was caused by a storm, it makes a nice easy report and we can give it the tick for the loss adjuster and the insurance company to keep going with the process.

Sayla: Without that kind of evidence, it can be really hard to prove if something was done during a storm. I mean, there’s some obvious things: If something’s pre-existing and it’s got a, you know, a plant growing through it, well, then it didn’t happen yesterday, but for the most part, it’s really hard to say in black and white.

Sayla: Number twenty: “My insurer rejected my claim. Can an engineer’s report help?” Yeah, if they rejected your claim, they usually have good reason to do so. If you disagree with the reason, then perhaps you get a third party involved. If you have an engineer’s report that says, you know, if you’ve got an RPEQ backing that they they disagree with the insurer’s claim, then then perhaps you’ve got ground to stand on to take next steps, but—

Matt: The reason for the claim rejection matters a lot at this point, and an engineer doesn’t necessarily override an insurance company; we can’t tell insurance companies to accept a claim. Even if the report or the claim and the dispute go to mediation or even AFCA in Queensland, it’s still not a slam dunk that if you get an engineer involved, you’re going to get a good outcome. It really depends on the damage, and structural engineers won’t, for the most part, put their neck out too much; they’ll only say what they can prove, especially if it’s likely to go to court or a tribunal. We want to be able to stand up there and tell the truth, the whole truth, and all that, so it’s important that you can provide evidence, or engineers are looking for evidence just the same as the insurance company was. If there’s been an obvious mistake, then maybe a structural engineer can help point out that mistake, but insurance companies are pretty good at what they do, they look for damage every day, they justify or work out how old the damage is, and structural engineers can’t override insurance necessarily. It’s maybe worth a chat, but it’s definitely not a slam dunk.

Matt: We’ve got a question come in, it says: “Good morning, do you have guidance for how to assess where the line in the sand is when considering either renovating an existing part of a heritage style house versus demolishing?” Well, typically, if the house is character—in a character zone—you don’t have a lot of choice if it you’ve got to at least keep the front facade, and your town planner will tell you how much other than that you’ve got to maintain if it’s a heritage style and it’s in a character overlay. As structural engineers, I have seen reports—they won’t be done by us—that say the house is just so terrible that you can’t maintain it, can’t do anything with it, it’s got to be demolished, not the sort of thing that we’ll do, but I know that there are engineers in Brisbane who’ll write reports like that, that then have to be accepted by council, the town planner, and and council, the people that are making the decisions on whether or not you can demolish it.

Matt: As far as whether or not you should, if it isn’t character overlay and it’s not protected and it’s not on a heritage list or something, I guess it depends on where you’re headed. So, you might be looking—if it’s a renovation, a lot of the stuff, if you’re making changes inside the structure, the old timbers are—if they’re fully termite-eaten or they’re in the wrong place, you’ve got the opportunity to move some of those timbers around. Still going to have to re-support the roof and also that front facade, so there’s that. I guess it depends, case-by-case, is there a line in the sand? No, it involves town planner, council rules, a structural inspection, someone saying whether or not what your ideas are are feasible, a good designer slash architect, and if it’s actually heritage-listed, then a heritage consultant to locate the paperwork for that heritage listing, work out what you can and cannot do to the structure because those rules are way over our head as structural engineers, we’ll have to comply with them, they’re not the sort of thing we can make a decision on. But the renovation, I guess, if you’ve got an older home and it’s not heritage-listed and it’s not in a character overlay, it really comes down to how much work do you need to do to get it to what you want to do? Are you turning a bedroom into a large room, a large lounge room, and most times, for even older homes, really old homes even, we can get away with putting in some beams and some extra bracing, and we don’t specify that the whole house needs to be demolished. The cost comes down to whether or not—or where you’re headed and what your budget is, if you’ve got enough money, you can probably even convince—you can do a full re-gut and re-build, it’s been done before as well. But it, like, it really depends on the budget, where you’re headed, so it’s not an existing line in the sand, we can provide advice, but there’s a few steps before you get a structural engineer involved.

Sayla: You might also find that when it comes to renovations, there’s a more—there’s almost always more hidden costs than you assume there’s going to be at the beginning of a project, you just you never know what you’ll find once you start actually ripping down plasterboard and seeing how things are built, so if you are going to go the renovation route, maybe just giving yourself a little bit of extra leeway in terms of expenses. The demolish and rebuild, just the demo alone, before you go ahead and get all your plans drawn up and do a rebuild, it can be an expensive route to go, but there is the peace of mind of knowing that you’ve got something fresh with no hidden surprises, you can maybe budget for it preemptively, and know more about what you’re going to get into in terms of cost, but that a new structure would be built to current standards, which of course is the best we have so far, and renovating an old structure is trying to improve what’s already there, which may or may not be good, so little bit of risk involved there, yeah.

Matt: My cherry-picked question is: “How do you assess reinforcement in existing concrete without demolishing it?”

Sayla: I just had a phone call about this. Obviously, an engineer showing up on site and looking at a concrete slab doesn’t know what’s necessarily beyond the concrete. And there are a lot of reasons why you might want to look at it if you want to do improvements to a structure, for example, and you need to know if it’s going to be able to—if you can just build on top of it or if you need to improve the foundations. How do you understand what’s in the concrete, specifically reinforcement? So, there’s two things you can do: One is to get the structure scanned, so there’s all sorts of scanning services across Queensland where they basically show up and they scan the concrete and they’re able to put together a little map for you and tell you exactly what’s in there, it can be a little bit vague, but it gives you an understanding on at least if it’s minimally reinforced and what sort of improvements you need. The other thing is, you wouldn’t believe what you can find through the council if you request documents for your home; there’s often—well, especially for newer builds, but for modern construction, there will likely be a paper trail and ideally, a set of engineer’s drawings that can tell you exactly what’s in the ground.

Matt: Yeah, and worst comes to worst, is it such a major structure that it can’t be demolished anyway and started again? But, yeah, the concrete scanners and ground-penetrating radar and their reports- we use them in court; we use them in tribunal; they are reliable enough that we can tell where the reinforcement is, not necessarily how big the bars are, but at least we’ll get an understanding of how deep they are in the concrete and what sort of spacing.

Matt: From our adjusted starting time, we’ve still got about nine minutes to go. If you’re watching and you’ve got a question, you’ve still got like three minutes that you could type something into the comments and and ask your question now, and I guess we’ll cherry-pick out of the 12 questions that we haven’t got to yet.

Matt: On that happy note, that’s our one hour or 59 minutes, which is near enough. I’d like to thank everyone for joining us, really apologise for the and to you, too, Sayla, for the first attempt where we didn’t have any sound, um, thank you very much for joining us, thank hope you got something out of this, and we’ll catch up with you later. Catch you later, bye.

Sayla: Thanks, guys.

Matt: Well done.

Causation: The word that sits at the centre of almost every disputed building insurance claim.

It is not a complicated word.

But once you understand what it means, and how structural engineers use it, you will understand why some insurance claims are accepted, reduced or denied.

The word is causation.

In plain English, causation is the link between the event and the damage.

Did the storm cause the damage?
Did the tree impact cause the damage?
Did the vehicle impact cause the damage?
Did the flood cause the damage?
Or was the damage already there before the event?

That is the question that often decides the outcome of a claim.

What causation actually means

When a homeowner makes an insurance claim, there is usually an event.

A storm.
A tree impact.
A vehicle impact.
A flood.
A burst pipe.
A cyclone.
An earthquake.

The event itself is only part of the story.

The insurer then needs to decide whether the damage being claimed was caused by that event, or whether it was caused by something else.

That “something else” might be gradual deterioration, wear and tear, poor maintenance, defective construction, long-term movement, corrosion, decay, previous damage, or a pre-existing defect.

This is where claims often become difficult.

A homeowner may see the damage after the storm and reasonably say, “That happened because of the storm.”

The insurer may look at the same damage and say, “No, that was already happening before the storm.”

The structural engineer’s job is to look at the physical evidence and provide an opinion on what is more likely.

Your home has a history

One thing homeowners often do not realise until they go through a claim is that their home has a history.

It has been rained on.
It has moved.
It has expanded and contracted.
It may have settled.
It may have cracked.
It may have been patched and repainted.
It may have had drainage problems.
It may have been poorly detailed or poorly built in some areas.

None of that automatically means the claim is invalid.

Older buildings can still suffer legitimate storm damage.
Buildings with defects can still be damaged by an insured event.
A pre-existing issue does not automatically explain every piece of damage observed after a storm.

But the history of the building matters because it can affect the causation opinion.

A claim is not just about whether damage exists. It is about why the damage exists.

Why causation gets disputed

Most disputed claims turn on the same basic argument.

The homeowner says:

“The damage happened because of the storm.”

The insurer says:

“The damage was pre-existing, or it was caused by gradual deterioration, defective construction or maintenance issues.”

That argument is common because insurance generally responds to events, not to the normal ageing of a building.

The hard part is working out where the line is.

Some damage is obviously new.
Some damage is obviously old.
Some damage sits in the middle.

That is where the engineer needs to inspect carefully, record the evidence and explain the reasoning.

A causation opinion should not be a guess. It should be an opinion based on the condition of the building, the damage pattern, the history provided, the photographs available, and the likely behaviour of the structure.

What happens when an engineer arrives on site

When I attend a property after an insured event, I do not usually start by staring at the crack or damaged member in isolation.

I usually start by talking to the homeowner or occupant.

I want to understand what happened, when it happened, and what changed after the event. I want to know what they saw, what they heard, what was damaged immediately, what was repaired or made safe, and what they believe was already there before the event.

That information is useful.

But it is not the whole investigation.

After being shown through the property, I like to go back through and form my own view. I take photographs. I record the damage. I look at the location, size, shape and pattern of cracking or structural distress. If cracks are relevant, I record widths where useful. If structural members are damaged, I look at how they are damaged and whether that damage makes sense in relation to the claimed event.

I also like to start wide and work inwards.

That means looking at the property from the street, around the outside, across the site, and then into the building.

What type of building is it?
How old is it?
What is it made from?
What is the roof form?
What is the wall construction?
What is the site doing?
Are there trees nearby?
Is there evidence of drainage problems?
Is there evidence of older movement or deterioration?

That context matters.

A crack in isolation tells you something.
A crack in the context of the whole building tells you more.

Connecting the damage to the event

Some causation investigations are straightforward.

If a tree has fallen through the roof, there is damage to the roof framing, ceiling framing and wall framing directly below the impact zone, and the photographs show the tree on the house, then the causal link may be obvious.

The event happened.
The damage is in the right location.
The mechanism makes sense.
The physical evidence lines up.

But storm damage is often harder.

For storm-related claims, the question is not simply whether there was a storm. The question is whether the storm is likely to have caused the damage being claimed.

Weather records can help. They may tell us what conditions were recorded near the property. But they do not usually tell us the exact wind speed at the exact house.

The wind speed at a nearby weather station is not necessarily the wind speed at the damaged building. Local terrain, shielding, surrounding buildings, trees, slope, exposure and building height can all affect the actual wind loads experienced by the structure.

So weather records are part of the picture, not the whole picture.

The engineering question is whether the damage observed is consistent with the likely effects of the event.

For example:

Is the damage in a location that makes sense for wind loading?
Is it on a part of the building that would be vulnerable?
Do the roof and wall connections explain the damage pattern?
Is there a logical load path between the event and the damage?
Is the damage fresh, or does it show signs of long-term deterioration?
Does the failure mode look sudden, or gradual?

That is the sort of reasoning that should appear in a causation report.

The pre-existing defect argument

This is where many homeowners feel blindsided.

An insurer may say that the damage was not caused by the insured event. It was already there. Or it was caused by wear and tear, defective workmanship, poor maintenance, corrosion, decay, long-term movement or some other pre-existing issue.

Sometimes that argument is right.

Sometimes it is not.

A pre-existing defect does not automatically mean the claim should fail. A building can have an existing weakness and still suffer event-related damage.

For example, an older roof may be more vulnerable than a new roof. That does not automatically mean storm damage to that roof is not storm damage.

The real question is what caused the damage being claimed.

Did the storm cause new damage?
Did the storm make existing damage worse in a meaningful way?
Was the building already so degraded that the event was not really the cause?
Was the storm simply the moment when an existing problem was noticed?

These are not always easy questions.

But they need to be answered with evidence, not assumptions.

If a report says damage is pre-existing, it should explain why. It should point to physical evidence. That might include old staining, corrosion, previous patching, dirt inside cracks, weathered fracture surfaces, long-term distortion, historic photographs, previous reports, or a damage pattern that does not line up with the claimed event.

A statement that damage is pre-existing is not enough.

The reasoning matters.

An insurance causation report is an opinion — but not a loose opinion

This is an important distinction.

A causation report is often an opinion.

It is not always a design.
It is not always a calculation package.
It is not always a certification.
It is not always a set of repair drawings.
It is not always a construction specification.

In many insurance matters, the report is an expert opinion about whether the damage observed is likely to have been caused by the insured event.

But that does not mean all opinions are equal.

An opinion can be careful, evidence-based and well reasoned.
Or it can be shallow, selective and poorly explained.

The value of the report is not just in the conclusion. The value is in the reasoning.

A useful causation report should explain:

What was inspected.
What information was provided.
What damage was observed.
What evidence was available.
What damage is likely to be related to the insured event.
What damage appears to be unrelated or pre-existing.
Why that conclusion has been reached.
What further investigation or repair is recommended, if that forms part of the scope.

The report should lead the reader through the logic.

It should not just say, “This was caused by the storm,” or “This was not caused by the storm.”

It should explain why.

What a Cornell Engineers causation report usually contains

Our reports are generally broken down into a practical structure.

What did we see?
Is it likely to have been caused by the insured event?
Why or why not?
What needs to happen next?

The report will usually include the brief, the property details, the scope of inspection, observations, photographs, discussion, conclusions and recommendations.

The scope is important.

A visual inspection is not the same as a full invasive investigation. If wall linings have not been removed, roof spaces are not accessible, or concealed structural elements cannot be seen, the report needs to say that.

Limitations are not a weakness. They are part of honest reporting.

The photographs are also important. They allow the reader to see what the engineer saw, and they help anchor the opinion to actual physical evidence.

The conclusion should then follow from the observations.

If the report jumps from photographs to conclusion without explaining the reasoning, it is weaker than it should be.

Why qualifications and local experience still matter

A report does not become correct just because an engineer signed it.

Engineers can be wrong.
RPEQs can be wrong.
Insurer-appointed engineers can be wrong.
Homeowner-appointed engineers can be wrong.

The signature is not what makes the opinion right.

The reasoning is what matters.

That said, qualifications and experience do matter.

A local structural engineer who understands how Queensland houses are built, how older houses behave, how roof and wall framing is commonly connected, how buildings deteriorate in our climate, and how local construction practice has changed over time is usually better placed to provide a useful opinion than someone who does not have that background.

That is particularly important when the report moves beyond simple observation and into structural engineering judgment, structural adequacy, load paths, repair methodology, compliance, design or certification.

There is a difference between a general opinion and professional engineering services. The distinction depends on the nature of the work being performed.

For homeowners, the practical point is this:

Do not just look for a report. Look for a sound report.

Who prepared it?
Did they inspect the property?
Do they understand the type of building?
Does the report explain the reasoning?
Does the conclusion follow from the evidence?

Red flags in causation reports

Some insurer-commissioned reports are thorough, fair and well reasoned.

Others are not.

The same can be said for reports commissioned by homeowners.

The question is not who paid for the report. The question is whether the report is sound.

Red flags include:

• A conclusion that is not supported by specific evidence.
• A report that relies heavily on general statements.
• A report that says damage is pre-existing but does not explain why.
• A report that ignores relevant photographs or history.
• A report that does not clearly identify what was inspected.
• A report that treats visible deterioration as proof that all damage is unrelated.
• A report that fails to separate old damage from new damage.
• A report that does not explain the damage mechanism.
• A report that appears to be mostly template wording.
• A report prepared without a site inspection, where a site inspection was reasonably possible and important.

Desktop reviews can have a place, especially when reviewing existing documents and photographs. But a causation opinion based only on photographs provided by others will often be weaker than one based on a physical inspection of the property.

Again, it comes back to evidence.

Assumptions are not findings.

What homeowners should do in the first 48 hours

If the structure is not safe, stay out of it.

That is the first point.

If it is safe to do so, take photographs and videos as soon as possible after the event.

• Take wide photos.
• Take close-up photos.
• Take photos from outside.
• Take photos inside.
• Take photos of every room.
• Take photos of the roof if you can do so safely from the ground or by drone.
• Take photos before make-safe works.
• Take photos after make-safe works.

The reason is simple.

The building changes quickly after an insured event.

Branches are removed. Roof sheets are lifted. Damaged materials are stripped out. Temporary supports are installed. Tarps are added. Ceilings are removed. Debris is cleaned up.

By the time an engineer attends, the building may look very different from how it looked immediately after the event.

That does not mean the claim cannot be assessed. It just means the evidence may not be as good.

Good photographs help everyone.

• They help the homeowner.
• They help the insurer.
• They help the builder.
• They help the loss adjuster.
• They help the engineer.

They may also help later if the matter ends up in an internal review, AFCA complaint, building dispute, legal process or tribunal.

Pre-event photographs are even better

The best evidence is often the evidence taken before there is a problem.

Every six months or so, take photos of your property.

Photograph the outside. Photograph the roof from the ground. Photograph retaining walls, decks, fences, ceilings, walls, wet areas and any existing cracks or movement.

You may never need those photos.

But if there is a storm, impact, flood or other insured event, they may become very useful.

• They can show what was already there.
• They can show what changed.
• They can help separate old damage from new damage.
• They can reduce argument.
• They can make the engineer’s job easier.

In insurance work, good evidence matters.

What if the insurer’s report may be right?

This is a difficult part of the process.

Sometimes the insurer’s report is broadly right.

That can be hard for a homeowner to hear, especially when they are stressed, tired, living with damage and feeling let down by the process.

But the engineering opinion still needs to be honest.

If the damage is not logically related to the insured event, or if the physical evidence suggests it was already there, the report needs to say that.

That does not mean the homeowner is being difficult.
It does not mean the building does not need repair.
It does not mean the insurer is right about everything.

It simply means that the damage may not be damage that can properly be attributed to the insured event.

That distinction matters.

What if the report does not add up?

If you receive a causation report and the conclusion does not make sense, do not focus only on the last paragraph.

Read the reasoning.

Ask:

• Does the report correctly describe the damage?
• Does it identify the claimed event?
• Does it explain the link between the event and the damage?
• Does it explain why damage is said to be pre-existing?
• Does it rely on photographs, measurements or physical evidence?
• Does it ignore relevant information?
• Does it explain the limitations of the inspection?
• Does the conclusion follow from the observations?

If the answer is no, the report may need to be challenged.

The usual starting point for an insurance claim dispute is the insurer’s internal review or complaint process. If the dispute cannot be resolved there, AFCA may be available for eligible general insurance complaints.

In Queensland, QCAT may be relevant in some related disputes, but that depends on the nature of the dispute. A dispute about an insurer’s decision, a domestic building dispute, a QBCC-related issue, a consumer/trader dispute and motor vehicle property damage are not all the same thing.

The correct pathway depends on what the dispute is actually about.

Homeowners should obtain legal advice if they are unsure which process applies.

How to challenge a denied or reduced claim

If a claim has been denied or reduced because of causation, the process usually needs to be handled calmly and in writing.

First, ask for the reports the insurer relied on.

Read them carefully. Look for the reasoning, not just the conclusion.

Second, ask the insurer for an internal review if you do not accept the decision.

Set out the reasons clearly. Do not just say you disagree. Explain what part of the report appears wrong, incomplete or unsupported.

Third, consider obtaining independent engineering advice.

If the dispute is about an engineering conclusion, it is difficult to challenge that conclusion without proper technical evidence. A homeowner’s frustration may be completely understandable, but frustration is not the same as evidence.

Fourth, use the appropriate dispute pathway.

For many general insurance complaints, AFCA is the external dispute resolution body. Other pathways may apply depending on the nature of the dispute.

The main point is to follow the process, keep records, and build the case around evidence.

What distinguishes homeowners who get better outcomes

The homeowners who do best in this process are usually not the loudest.

They are the most organised.

• They have photographs.
• They keep records.
• They communicate in writing.
• They stay calm enough to focus on the evidence.
• They ask for reports.
• They read the reports carefully.
• They obtain independent advice where it is needed.
• They follow the complaint process.

That does not guarantee success.

Sometimes the insurer is right. Sometimes the damage is pre-existing. Sometimes the engineering evidence does not support the claim.

But when the insurer’s causation opinion is weak, incomplete or wrong, a calm, evidence-based approach gives the homeowner the best chance of a fair outcome.

A note on the emotional side

A building insurance dispute is not just a technical process.

It is personal.

Your home has been damaged. You may be living with temporary repairs, water damage, structural damage, uncertainty, delays and financial pressure. You may feel like no one is listening.

That is hard.

As engineers and consultants, we need to remember that homeowners are often dealing with this process at one of the worst times in their lives.

At the same time, the process still works best when everyone stays civil and evidence-focused.

Give the engineer the information they need. Provide photographs. Provide dates. Provide previous reports if you have them. Explain what changed after the event.

But also give the process room to work.

Good evidence, properly presented, through the right channels, can make a real difference.

How Cornell Engineers can help

Cornell Engineers prepares independent structural engineering reports for homeowners, insurers, builders, loss adjusters, solicitors and dispute matters.

If your insurance claim has been disputed, reduced or denied, and the issue involves structural damage or causation, we can inspect the property and provide an independent opinion based on the visible evidence.

We can also review reports prepared by others.

Sometimes that review will support the homeowner’s concern. Sometimes it will confirm that the insurer’s report is broadly reasonable. Either way, the advice needs to be straight.

That is the role of an independent engineer.

We are not there to simply argue for whoever pays us.

We are there to inspect, record, reason and explain.

Final thought

Causation is not always simple.

Some damage is clearly caused by an insured event. Some damage is clearly pre-existing. But a lot of insurance claim work sits in the middle.

That is where evidence matters.

A good causation report should explain what was seen, what probably caused the damage, and why that conclusion makes sense.

• It should not be a guess.
• It should not be advocacy.
• It should not be a template conclusion looking for a property to attach itself to.

It should be a clear, fair and evidence-based opinion.

That is what homeowners, insurers and decision-makers should expect.

When a storm rips through a roof, or a fallen tree cracks a wall, most homeowners have the same question: is this actually structural, and how do we prove it was caused by the storm?

Matt Cornell, Director of Cornell Engineers, recently sat down to walk through exactly how that process works — from the first site visit through to the final report. Here’s what he had to say.

Here’s the transcript if you would prefer to read it:
Interviewer: Today we’re talking about insurance building claims after storms or major weather events. When you first arrive at a property where the owner believes the event caused the damage, what are you looking for before you form any opinion?

Matt Cornell: I try not to enter an insurance claim job with too many preconceptions. I have an understanding of what the claimed event is, but I don’t necessarily know all the specifics. So I’ll ask the insured homeowner to tell me what happened, when it happened, whether they were home at the time, and what they noticed. Then they’ve got the opportunity to walk me around the property and give me a good idea of what they think is going on. I take photos and listen, and the inspection progresses from there.

Interviewer: Once you’re listening to them and walking through their observations, what’s the first physical detail you want to check to start distinguishing event-driven damage from something pre-existing?

Matt Cornell: It’s really difficult for an engineer, or anyone, to identify new damage compared to old damage without prior knowledge of the building — that’s almost impossible to get. There are online references, real estate photos, and sources like Google Street View, but at the end of the day we’re relying on the homeowner’s description, our knowledge of the event, and some research back in the office to form an opinion on whether the claimed event has possibly caused the damage we’re being shown.

Interviewer: So once you’re back at the office doing that research — checking weather data, event records, or historical photos — what specific physical clue or inconsistency would make you pause and reconsider your initial impression?

Matt Cornell: If the damage shows up in real estate photos, or if it looks like someone has been careful to scrub an area, we’ll pull on that string. We might contact the real estate agent to get photos taken before they were uploaded to the system, or even go to the original photographer. We’re looking for photos — maybe from the insured person if they had a party in the room, and there’s the wall, floor, or roof in the background — that show the property was fine before the insured event and damaged after it. That pre-existing condition prior to the event is what we’re really interested in, to confirm the damage was caused by the insured event.

Interviewer: Why does confirming that timeline matter so much for what happens next for the homeowner?

Matt Cornell: Causation is a big part of why an engineer gets invited to a site. An insurance company wants to be assured the damage was caused by the insured event — that determines how they handle the claim. Often, alongside causation, we’re asked to provide drawings, rectification advice, or repair details. If a tree has hit a roof and broken the trusses, an engineer gets involved to provide details for the insurance company and builders to quote and carry out the work. Where it’s non-structural — say, cracks in plasterboard — we’re asked for an opinion on whether that could have been caused by the insured event. If it has, and it’s not structural damage, there’s still rectification required, but it won’t necessarily need a full scope from a structural engineer.

Interviewer: If you determine it’s not structural, but the homeowner still sees it as major damage, how do you explain that in a way that reassures them without minimising what they feel?

Matt Cornell: Structural elements are a lot stronger than most people realise. The wall frame and studs — especially in modern construction, and arguably more so in older hardwood-framed construction — are stronger than most people give them credit for. It takes a fair bit of damage for a building to become structurally unsafe or irreparable. So when we’re talking about cracks in a wall, the plasterboard is typically aesthetic — it’s not part of the main structure — and there’s a certain amount of reassurance we can give homeowners. But some homeowners are a long way down the track by the time an engineer gets there, having worried about their wall or the structural stability of their property for a long time, and it takes some persuading to explain that the plasterboard isn’t part of the structure — the frame is. Quite legitimately, they might then ask how we know the inside hasn’t also been damaged. The answer is that when plasterboard is cracked, it’s often replaced under the claim, and that gives the structural engineer or builder the opportunity to inspect the frame once the cladding is stripped out and confirm whether it needs repair. Often the cladding has already been removed by the time we get on site, so we can assess the structure visibly for damage and advise on rectification.

Interviewer: Once you’ve confirmed what’s structural and what’s not, what would you typically outline as next steps if you’ve found a genuine structural issue?

Matt Cornell: Next steps are fairly straightforward — we’re qualified and experienced to provide rectification details. We might provide drawings showing what work needs to be completed, how far that extent goes — a whole wall or just part of one — what the replacement members are, and which timber sizes to use. For framing over a window or doorway, we’ll give the insurance company sizes for new timber members, not necessarily identical to the original, because load codes and timber availability change over time. If the old member was a certain grade of pine, we might specify a different grade depending on availability and what the insurance company’s coverage allows. For an old, heritage-listed house with damaged hardwood, there’s a good chance it will go back like-for-like to maintain the heritage character.

Interviewer: When you’re writing that final report, what do you always make sure is clearly detailed, and what do you deliberately avoid saying or speculating on?

Matt Cornell: We always include photographic evidence and the research that helped us form an opinion — including sources like realestate.com.au. That validates where our ideas came from and why we’re saying what we’re saying. We generally won’t include extracts from current standards, because we’re providing drawings and a set of standard notes and details on how to do the work instead. What we’ll almost never do is state definitively that damage was not caused by the insured event — because we weren’t at the property before the loss occurred, so we don’t know for certain. We use engineering principles and experience to form an opinion on whether the damage is attributable to the insured event, but we’ll frame it in terms of likelihood, not certainty.

Interviewer: When you hand that report over, what’s the key thing you want the client or insurer to understand about how to move forward?

Matt Cornell: We provide our reports to building consultants so they can put together a scope of work for the insurance company, which then gets distributed to builders. So the report needs to clearly identify what aspects need to go into that building scope — that’s really the core of it.

Interviewer: In your experience, what’s a common misconception about structural damage or repair that you often have to correct?

Matt Cornell: Homeowners, and even insurance companies, aren’t always aware that the age of a building affects what a repair can realistically achieve. The expectation is often that a repaired building will come out essentially as good as new. Builders can do a certain amount of work on an old house that doesn’t meet current standards, but they’re unlikely to guarantee bringing the whole building up to current standards — and engineers can’t help with that either. We do a good job of repairing damage and getting a building back to better than it was before the damage, but that’s not always the same as bringing it to current standards. Some buildings were never fully compliant to begin with. We’re happy to answer specific questions — for example, whether new roof sheeting will be safe and comply — but we’ll never say a whole building we haven’t fully inspected is now compliant with current standards. There’s a certain scope that a rectifying builder or engineer can reasonably work within. Sometimes builders go further than expected because they’re guaranteeing their own work, which offers them some protection — but that doesn’t mean a homeowner is entitled to a brand-new home just because part of it was damaged.

Interviewer: Let’s shift into how you communicate this to clients in plain English. What’s your key principle for explaining complex findings so they feel understood?

Matt Cornell: We try not to make it too complex when explaining things to an insured person. But we’re also writing the report for the insurance company, the building consultant, and the loss adjuster — a lot of people read it — so we avoid heavy technical terminology and try to keep it readable, so people understand what happened, what we think, and what needs to be done. They can then draw their own conclusions, and if they want further engineering advice, they’re welcome to get an independent opinion from another engineer.

Interviewer: Let’s touch on what goes into being an expert witness in these disputes. What shifts for you in that role?

Matt Cornell: Expert witness work increases the stakes dramatically — everything we say, do on site, and write is going to be scrutinised by people doing their best to find reasons we haven’t done a good job, or that we’ve made a mistake or miscommunicated something. It’s a lot more stressful. We’re more careful, and we justify our decisions just as carefully as we always do — but with the added awareness that there’s a dispute in play.

Matt Cornell: And for anyone who’s watched this far — you’re welcome to put your questions in the comments below. I’d love to hear your experiences with insurance events, building consultants, and structural engineers assessing your property. What went right, and what went wrong? I’m Matt Cornell from Cornell Engineers. I hope this has been useful, and I’ll catch up with you next time.

It starts with listening, not assuming

Before forming any opinion, Matt avoids walking onto a site with preconceptions. The process starts with the homeowner: what happened, when, whether they were home, and what they noticed. From there, a walkthrough of the property, photos, and observations begin to build the picture.

Separating new damage from old damage is the hard part

Without knowing a building’s history, distinguishing storm-caused damage from pre-existing wear is genuinely difficult — for any engineer or consultant. Real estate listing photos, Google Street View, and homeowner-supplied images from before the event are often the most reliable evidence available. If damage appears in earlier photos, or if an area looks like it’s been deliberately cleaned up or altered, that’s a signal worth following up — sometimes as far as contacting the real estate agent or original photographer for unedited images.

Why causation matters so much

Confirming that damage happened because of the insured event is the entire reason an engineer gets involved. It determines how an insurer handles the claim, and whether the required work is a full structural scope (think broken trusses from a fallen tree) or a lighter non-structural fix, like plasterboard repair.

Cracked walls usually aren’t as serious as they look

One of the most common misconceptions Matt deals with: a cracked wall doesn’t necessarily mean structural damage. Plasterboard is largely aesthetic — it sits over the frame, which is typically far stronger than most homeowners assume. When plasterboard is replaced under a claim, it also creates an opportunity to inspect the frame directly and confirm whether any deeper repair is needed.

What a good report includes — and what it deliberately doesn’t

Every report includes the photographic evidence and research that shaped the opinion — including sources like real estate listings. What it won’t include is a definitive claim that damage was not caused by the insured event, since no engineer was on-site before the loss occurred. Reports are written in terms of likelihood, based on engineering principles and experience, not certainty.

A repaired building isn’t a new building

A significant misconception among homeowners and even insurers: a repair should bring a building fully up to current standards. In reality, builders and engineers aim to restore a structure to better than its pre-damage condition — not necessarily to full current compliance, especially in older buildings that were never fully compliant to begin with.

Plain English, on purpose

Because a structural report gets read by insurers, building consultants, loss adjusters, and homeowners alike, Matt’s team deliberately avoids heavy technical jargon — aiming for a report that anyone involved can actually understand, with the option to seek independent advice if needed.

When it becomes expert witness work

When a claim turns into a dispute, the stakes change. Every observation, decision, and written word is open to scrutiny from people actively looking for gaps. It’s a more demanding version of the same rigour Matt applies to every job — just under closer watch.

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Have you had a structural engineer or building consultant assess storm or insurance damage on your property? Matt would love to hear about your experience — good or bad — in the comments on the video.

Matt Cornell | Cornell Engineers | Brisbane

Once again we’re sharing this video by James Cook University. This time it is for #Brisbane builders and homeowners to be aware of.

Also some additional resources for builders:

Repairing storm-damaged roofs

https://www.hpw.qld.gov.au/__data/assets/pdf_file/0026/3959/repairing-storm-damaged-roofs.pdf

Repair of sheet metal roofs in cyclonic areas

https://www.timberqueensland.com.au/Docs/QBCC_TimberQLD_20150223_MetalRoofGuide[1].pdf

Stay safe and I hope you don’t need our help – but we’re here if you do.