Tips & Tricks

When Do You Need a Structural Engineer

When Do You Need A Structural Engineer?

If you are building or extending in Queensland, these are the circumstances when you will need to engage a registered structural engineer (RPEQ):

  1. any suspended concrete floors;
  2. the slab/footings design for structures located over or adjacent to any sewer or water mains;
  3. the slab/footings design outside the scope of Australian Standard AS 2870;
  4. high tie-down loads nominated by the truss supplier as requiring specific engineering design;
  5. if the structure has steel members;
  6. retaining walls over 1.0m high.

The other design components including bracing and general tie down, wall framing and floor framing can be calculated and shown on the building designer’s drawings.

Of course, Cornell Engineers can show these elements for your new house or extension too, and sometimes it’s easier if we DO show these elements – but ask your engineer and designer to see who should do the work for your specific project.

When Do you Need a Soil Test

An extract from a recent application: A soil investigation report (conducted by a certified person or company) must be provided with any building application for a new dwelling, major extension to a dwelling or the like. The soil test report must be addressed to the property owner and the assessment manager, clearly flagging that the report is for use and reliance by the assessment manager.

What the Soil Test Should Show

Reports require the following:
• be dated; and
• include a unique document number (with a revision code for amendments); and
• indicate the name of the person who prepared the report; and
• be reproduced at A4 size; and
• be capable of black and white photocopying without affecting the clarity of graphics.

Home Maintenance and Repairs Tips & Tricks

Slab Heave – Waffle Slab vs Conventional Raft Slab

What is Slab Heave?

Slab heave occurs in a house concrete slab when the ground moves more than your slab can stand. Waffle slabs and raft slabs are both intended to moderate this ground movement to acceptable limits.

The slab doesn’t normally crack, but if the movement in the slab is more than the brickwork and/or plasterboard walls can tolerate: they crack.

Slab Heave – Waffle Slab vs Raft Slab

Which is better? A waffle slab or a raft slab?

Waffle slab structural engineer
Waffle slab setup before concrete

The quick answer:

A Raft Slab


  • Waffle slabs are built on top of the ground and need great drainage and really hard ground for the life of the building.
  • Raft slab footings are dug into the ground, have more perimeter stiffness and more tolerance to poor ground conditions than waffle slabs.
  • When turf and gardens are placed around waffle slabs, water can easily flow under the slab – that’s bad!
  • Poor site drainage is easily disguised. Even if the ground surface looks like it grades away from a waffle slab, builders often use sand and rocks around a house to bring up ground surface levels. Sand and rocks are porous and allow water to flow under a waffle slab. This is a major cause of slab heave in waffle slabs.

Are Waffle Slabs Legal

Waffle slabs are legal and are their design is covered by AS2870 so engineers are entitled to specify them. However, their use comes with a lot of provisions that relate to site drainage that must be observed for the life of the building.

Your best protection is to read the engineers plans and observe the rules. If you haven’t built yet, find out what the rules are and whether they will restrict your plans for gardens, trees, lawns and swimming pools.

Waffle Slabs Need Better Drainage

Waffle slabs are a lot less tolerant of poor drainage:

  • Site drainage is ULTRA-important but builders often only improve site drainage after the house is built. Water lying near a building under construction is against the engineer’s rules and can cause slab heave.
  • The site drainage rules apply for the life of the building but this important information often isn’t passed on to future owners.
  • Waffle slabs let moisture flow under buildings. This is the opposite of what is required for good performance of a house slab.

Damage from Slab Heave

Signs of slab heave include:

  • Gaps under walls
  • Damaged cornices
  • Uneven floors
  • Doors jamb and don’t close properly
  • Diagonal cracks in brickwork
  • Diagonal cracks in internal walls

Raft Slabs

You may have realised that we prefer raft slabs at Cornell Engineers. Want some reasons to pick a raft slab over a waffle slab? Check out this post.

Want to know more?  Here’s the link to our video on slab heave.

New Homes Tips & Tricks

Better Buildings for Brisbane

Builders take Note

I’ve worked for more than 20 years as a structural engineer in regions of Queensland that suffer the threat of cyclones. With Cyclone Marcia looming off Rockhampton at the time of writing, I’d like to address those new home builders in Brisbane that think they can relax because “Brisbane doesn’t get cyclones.”

Brisbane Doesn’t Get Cyclones

Fundamentally you are correct. And the benefit is you can build beautiful, big, high ceiling houses using a lot less timber than you can in cyclonic areas.

But if you as a builder are cutting corners to trim costs: I put you on notice. Brisbane still gets storms – and they can be furious!

Brisbane Homes need to Built Better

The building structures and building practices Brisbane builders are using to save money are well below what I consider adequate.

Brisbane builders you are also putting your clients – the new home owners – AT RISK if:

  • If you have cut the budget for your soil testing
  • If you have strong-armed your engineers to produce ‘cheaper’ designs
  • If you use a particular certifier because they don’t inspect quite as thoroughly

We Haven’t Done That Before

Too many times in my career as an engineer I have heard concreters and carpenters say ‘We’ve never had to do ‘that’ before.”

Well guess what. Building standards were improved a long time ago and it’s time you updated you practices.

Start Building Better

It’s time that substandard designs, cut price soil tests and poor building construction techniques are eliminated.

Australian standard AS1684.2 is the manual for residential timber construction and you should be using it. Storms DO happen in Brisbane area. Are the products you are producing going to pass the test?

A Message to Home Buyers

If you are a home buyer and you are about to build a new home, there IS a way you can get value for money, a good design and peace of mind in the next storm.

You cannot simply rely on what you are being told by the builder. You cannot even rely on what other customers are saying.

To be truly responsible for your own decision, the only way you can be sure you’ve chosen a good mass market builder is to inspect the buildings they are building.

And if, as my old neighbour used to say, “You don’t know shit from clay”; get some expert advice on your side.

An inspection by an independent inspector or structural engineer of a building being built by your builder will give you peace of mind.

Check Out the Workmanship

I have some suggestions for you for next time you walk through a display home:

  • Look for cracks in the concrete.
    • Some builders cleverly disguise the concrete surface their display homes with vinyl, carpet or spray on floor coverings. Under that surface is a representative sample of the concrete finish you can expect with your new home.
    • Ask to see the concrete! When it comes to cracks, you’re as good at spotting them as me. So look and find.
    • Cracks in concrete mean a variety of things and may not be a problem, but if you are looking for bang for your buck, then aesthetics are important. Builders know how to produce crack-free concrete but they rarely do. DO NOT accept substandard concrete.
  • Push on the walls. Find the tallest wall in the house – it might be a feature wall or a vaulted ceiling. Push on the wall! See if the wall moves. Push on another lower wall and see if it moves too. Some builders are using skinny sticks of timber in walls and they have been for years. There is no excuse. Regardless of wind classification or cyclonic region you are building in, the walls in your new house should be sturdy and SHOULD NOT MOVE when you push them.
  • Check your walls for straightness. A friend of mine had a new house built near my place. He asked me to look at it two months after he moved in. He complained that the walls weren’t straight. He could tell because the line of the tiles didn’t align with the walls. His walls were crooked. It wasn’t too late to fix because the building was still under warranty but it left him with a bitter taste in his mouth. After a lot of hard arguing and complaining, my friend had his walls straightened and the tiles re-done. Get in early. Check out the lines of the display home walls against the lines of the tiles. Don’t accept substandard workmanship.

Arrange an Inspection

If you have found a builder you like but you want a hand inspecting a house under construction please contact an independent building inspector.

An independent inspection at timber framing stage or concrete slab stage will give you the expert advice you need at a price much less then the hassle of a substandard building.

If this article has helped you please leave a comment.

This article was written by Matt Cornell of Cornell Engineers.

Tips & Tricks

Home Inspections

If you are buying or selling a home, I recommend you get a building and pest report every time. Not from a structural engineer – although some structural engineers can do this work – but by a full time pre-purchase building inspector. I’m a structural engineer and I always engage a professional building inspector when I buy a property – and I’ll tell you why.

Pre-purchase Building inspectors do a great job!

It’s that easy. They climb into places that I refuse to go. They find defects that no one else has ever found – particularly in roof spaces. The see problems and report on them and make you as a buyer aware of most of the issues in a building. You can then make an informed decision about your purchase.

I’ve heard people say that the exclusions and the disclaimers make most of the report void. I disagree. Certainly the risk of being sued for missing a defect compared the small fee that building inspectors receive isn’t worth it. However the information in a building report is definitely worth it. It is DEFINITELY worth it.

Should you Hire A Structural Engineer to do a Pre-Purchase Inspection?

My opinion is that “No. You should not use a structural engineer for a pre-purchase inspection”. Why? Structural engineers are very, very good at solving building problems but they aren’t quite as good at finding problems. Structural engineers can see what you can see when it comes to defects. They might be able to say WHY a defect has occurred, but I don’t recommend them for finding the problem in the first place.

Structural Engineer Home Inspections

I think structural engineers are exceptional at diagnosing problems in a building once they have been found. I suggest a pre-purchase inspection be complemented by a structural engineer’s inspection IF structural defects are found in your property.

I personally have been to lots of properties after a building and pest inspection. The role I play in fixing damage is described better in my post about how to fix cracks in your house.

So please, use a pre-purchase building inspector if you are buying a property. Engage a structural engineer if the inspection report finds structural issues that need diagnosis and rectification. it’s what we do. Good luck with your purchase!

Looking for a recommendation for a pre-purchase building inspector? Check our Our Friends page.


Tips & Tricks

Professional Indemnity Insurance

What is Professional Indemnity Insurance?

Professional Indemnity Insurance (PI Insurance) is designed to assist professionals that provide advice and services to customers in the event of a claim alleging breach of professional duty or misconduct.

For structural engineers, professional indemnity insurance helps protect a structural engineer from bearing the full cost of defending a negligence claim and the damages that could be awarded in a tribunal or court case. The negligence claim could be made in relation to faulty designs, partial failures or even building collapse.

Even if the engineering professional successfully defends a claim, the costs involved in preparing a defence against allegations can be financially oppressive.

Is Professional Indemnity Insurance Compulsory?

In Queensland, the Board of Professional Engineers advises that Professional Indemnity Insurance is not compulsory. Read Here. However I strongly recommend that all structural engineers carry PI Insurance with a minimum value of $1 million dollars.

Happy Engineer at Work
This Engineer is Protected by Professional Indemnity Insurance

How does Professional Indemnity Insurance help Customers?

Professional indemnity insurance gives customers peace of mind.

If you’re about to engage a structural engineer, find one that carries PI Insurance.

Mind you, professional indemnity insurance is a last line of protection for a professional structural engineer. A lot of things have to go wrong for a policy to be enacted:

  • A mistake has to be made.
  • It has to be missed by all those concerned with the design and construction process.
  • It has to be supplied, built and checked off by installers and suppliers.
  • The fault has to be detected by either a failure or early signs of failure. According to the news lately this all happs way too frequently.

All through this downhill process, communication and feedback process needs to be broken or stilted.

However mistakes still get made and still get built. Insurance is still required!

Should My Engineer have Professional Indemnity Insurance?

Professional Indemnity Insurance, like all types of insurance, is expensive and so not all structural engineers in Brisbane and Queensland carry professional indemnity insurance.

Cornell Engineers has a current Professional Indemnity Insurance policy. I think structural engineers that carry insurance show that they care about their customers.

Would you ever NOT insure your house?

No. To me it doesn’t make sense to have your home designed, renovated or repaired by a professional that doesn’t carry professional indemnity insurance.

So the answer is YES. Your structural engineer SHOULD carry professional indemnity insurance.

To compare quotes from two engineers – one that has PI insurance and one that doesn’t – is like comparing apples to oranges  (well actually – rotten apples). It just isn’t fair to compare one with the other. One cares for you, expects to do a good job, has protection and expects to be around in a few years. The other doesn’t.

How can Australian Engineers Arrange PI Insurance?

Our preferred insurance broker for professional indemnjty insurance is BRIC . Check out their website and have a chat about getting your engineering consultancy progfessional indemnity insurance up to date.

Does your Structural Engineer Carry Insurance?

To find out if your structural engineer structural engineer has a current professional indemnity insurance policy, you need to ask.

When you check your structural engineer’s Certificate of Currency:

  • it should be in date
  • it should have a limit of indemnity greater than your project value
  • it should specify the type of work the structural engineer is protected for

It’s your right and PI Insurance is for your protection too. Insist your structural engineer has a current professional indeminty insurance policy..