How to Fix Slab Heave

Slab heave can be fixed. The cracks in your house that open and close can be stabilised. Cornell Engineers has the experience and knowledge to help you fix slab heave in your home.

What is Slab Heave

Read “What is Slab Heave” and watch our video on Slab Heave.

Some signs of slab heave are:

  • Diagonal or stepping cracks in brick and blockwork walls.
  • Cracks coming from the corners of windows and doors.
  • Doors and windows stick and become difficult to open and close.
  • Cracks, gaps or compression of cornices.
  • Gaps under walls.
  • Visible unevenness in floors.
  • Rarely, cracks in floor tiles.
Diagonal crack in a rendered brick wall

Do This First

If you are a homeowner and your house is starting to move and crack, do this first:

  • Start a Crack Diary.
  • Find water sources that are entering the ground around your house and eliminate them.
    • Fix leaking pipes. Get a plumber to help find and repair broken and leaking pipes.
    • Repair dripping taps. Replace the tap washer or, better still, relocate the tap into your yard.
    • NEVER plant trees near your house. Consider removing any really large trees that are near your house (seek help from a structural engineer and/or arborist).
    • Fill in dog holes next to the footings with compacted moist clay sourced from elsewhere on the block.
    • Capture condensate from air-conditioners and hot water systems and divert it away from your house.
Slab heave causes gaps under walls or at the top of walls

Do these things before you talk to your builder. Do them before you lodge a claim with your insurance company. Do them before you start paying for engineers and expensive chemicals. Do them before you fix ANY damage.

What’s Next

The problems associated with slab heave can often be overcome by one of these solutions:

  • Improve the tolerance of the building to uneven movement. This solution includes articulation gaps and joints and wall strengthening but is only appropriate if the slab doesn’t feel uneven.
  • Remove the cause of the uneven movement. Identify sources of soil moisture and eliminate them or isolate the building from them.
  • Isolate the building from uneven movement. This method includes jacking and underpinning so that the house is supported clear of the ground movement. Not all houses can be fixed this way.
  • Demolition and reconstruction of the house using one or more of the above techniques and/or a stiffer/stronger footing system.

Do it Right

I’m sad to say – unless slab heave damage is repaired correctly, it will come back again, and again, and again. Concrete slab repairs have to be done correctly.

Some builders think that houses with slab heave damage can’t be repaired. Houses with slab heave can be stabilised!

Cornell Engineers have engineered successful repair and rectification projects many times. Matt Cornell has never had to recommend the demolition of a whole house because of slab heave.

Let me say that again: In twenty-eight years of full-time practice as a structural engineer, Matt Cornell has never ordered the demolition of a house because of concrete slab heave.

Should You Start Watering Around Your Home?

Changes in soil moisture levels in reactive clays cause ground movement. When clayey soils become wetter they lift. When clayey soils dry out they drop.

I’ve seen the results of engineers recommending to clients that they start watering around their homes. I’ve seen homes where the owner has installed boreholes that they fill up daily in an attempt to solve slab heave. I have seen automatic watering systems with the valve pit full to the brim.

Let me say this: The addition of water to the soil around your home by manual or even automatic methods is too uneven and too difficult to maintain for it to provide lasting results.

  • Do you stop watering when it rains?
  • Do you know whether you are changing the soil under your house?
  • To what degree is the moisture-wicking sideways?
  • Who will water for you when you are on holidays?
  • What will you do when there are water restrictions?

Do you see?

It is just to hard to maintain even soil moisture conditions around a house by adding water to the soil.

The better way to solve slab heave is to eliminate all abnormal sources of soil moisture. Go back and read the Do This First Section. All these things are aimed at providing long-term, stable, normally dry soils. No user intervention. No automatic watering systems or boreholes.

Make the soil dry around your house in a way that does not require your intervention. That is how you can protect your home from slab heave.

Cornell Engineers can Fix Slab Heave

If your house has moved and cracked because of uneven soil moisture conditions, let me help you diagnose and fix this problem. I can help you fix your concrete slab heave, reduce cracking and reduce ongoing movement.

In time you can fix the cracks and enjoy your house.

102 replies on “How to Fix Slab Heave”

Hi Matt,

Could this same concept of slab heave be a problem for houses on stumps? Our house on stumps has significant cracking around doors and windows as well as movement that requires releveling.

The side of the house with the most movement has:
– wet clay soil surrounding it (the soil is always quite wet and the grass is always very green – even when it has not rained)
– dry soil under the stumps (unless there is rain)
– a higher neighbour with a wooden retaining wall between us (retaining wall is 2m from our stumps)
– the higher neighbour has a drain in their yard (not sure if this connect to underground stormwater pipes or is a swale)

We really don’t know what to do. We have paid for an engineer and plumber who have given us advice that we were initially unsure about, but we are mores concerned now as your articles have so much detail they were missing.

Any help or tips is so appreciated!

Hi, we have a newly built house in a reactive soil area of Melbourne. Our builder used a waffle slab and the slab is only 1 year old but the garage is lifting through the centre. During construction the down pipes were never connected and water was pooling around the slab. We raised this multiple times but no action was taken. This is a home built with our lifelong savings and we were supposed to live here forever now but after 1 year we already have heave. Can you recommend a structural engineer in Melbourne as we do not trust our builder as they simply want to call back the people who laid the slab.

Hi Alex
Trust is one thing, but in Queensland you need to allow the builder accesss to try and fix the problem (if they will/can).
I’ll drop you an email with a name, but realise that the sandy soil that has been placed around your house is porous and is allowing water to pond where it used to pond when you could see it. Do what you have to and find those low spots and replace the porous fill with clayey fill.
Best regards
Matt Cornell

Thanks for the info. I have a Victorian era house on reactive clay soil which has developed bad cracking over the last few years. There was a leaky stormwater pipe which may be the cause. It has been fixed but the problem continues.

Can you recommend someone in Adelaide to advise me?

Hi Elinor
Fixing a leak like this in an older house is the correct first stop. Waiting for the ground misture conditions to stabilise is the next step. SlabSense has ground moisture meters that can help identify if/when the ground moisture has stabilised. Google them and ask about getting some sensors installed.
Matt Cornell

Hi Matt, thank you for all your info. My parents house in regional Victoria has dropped on all the edges after heavy rain last year. Can you please email me a structural engineer from Melbourne or Victoria.
Thanks again

Hi Yvette, I’m in regional Victoria and we’re experiencing the same issue. I’m in Echuca. The developers build on clay and then wash their hands of all the issues. Very frustrating.

Hi Matt
We have a home in Melbourne’s West – believe we too have been affected by slab heave due to clay soil moisture/movement.
Builder has suggested storm water risers and concrete paving to rectify at a huge cost.
Can you recommend anyone in Melbourne?

Hi Matt
We have a raised timber house built in the late 60s on the north side of Brisbane. Soil is clay I believe.
The timber floors have a noticeable hump in the centre of the house and every floor surface creaks and cracks. It drives us insane.
We’ve had several trades look at it and basically shake their head. I think it’s in the too hard basket. We have one crack in the brickwork on one side from subsidence (we gather). Does this sound like slab heave to you? Is this an issue your engineers would be able to inspect and offer a solution for. We are hopeful as we have been searching for an answer for years.

Oops. Sorry for the slow reply.
Hi Jennifer, a hump in the middle of an older house could well be slab heave. The good news is it doesn’t have to be a hard thing to fix. Houses that predate the current standards for footing and slab design do their own thing – they move from season to season as the soil moisture conditions vary. They don’t have the stiffness and overall system strength that we build into concrete slabs these days. The reason that is a good thing is that individual stumps can be adjusted up or down to suit the stump consensus – if one or two stumps are higher than the other stumps there is no reason those higher stumps can’t be adjusted down to match the stump neighbors.
So now the question is, “Who do you engage to do this work?”
A house-raising contractor is my suggestion. They have the gear to lift and lower houses. They understand older houses and how to adjust their height. Sometime they need jobs to do between major house raises and renovations. Your little stump adjustment job would probably be perfect.
Obviously, you can’t adjust the height of the brickwork walls very easily, so the adjustment needs to take into account those walls and parts of the floor that can’t be adjusted. Those brick walls become the fixed point for the floor and the other stumps become the adjustable parts of the floor.
I hope this helps.
Matt Cornell

I am having continuous cracking sound of my walls lifting up from ground my house is still under warranty and builders doing nothing can you please help me

Hi, I have slab heave only in the the summer if it’s been hot, my one storey extension is built on clay. Cause we’ve had a very hot summer with no rain the crack that shows has got bigger than ever. My front door is sticking badly now. Next door have some large over grown privet bushes less than a metre away from my extension and the cracking and subsidence is mostly on that side. Could this be the privet bushes causing the problem?

I have slab heave too and have done most of the points to solve it. We had a plumber come in today to check all hut the pipes and drainage is good. I have spent thousands lifting the back part of the house to be level to the front, have put concrete everywhere with minimum 2mt from the external walls and proper slope. No plants near the house. Yes I’m on clay soil ( Melbourne west). I can’t keep throwing money at this problem. Please give me some direction as on what to fo next.
Thanks for your time.

Hi Matt
Sorry to repeat the same question asked above. Could you please share the details of the structural engineers in Melbourne? I have been battling with slab heave issues at my new home in Melbourne West.

Hi Matt,
I believe I have slab heave issue. My rumpus suddenly has a uneven surface and my timber floor starts to crack. It starts a week ago.

I found my pergola has poor drainage as well.

I am located in Hoppers Crossing, Melbourne. Are you able to assist, please?

Thank you

Hi Matt

I got problem with sidewalk concrete moving and heave. Do you have anyone in Melbourne? Thanks in advance

Hi, thanks for all of the info on slab heave! Our old house has numerous cracks and is on clay soil. Advice that we have sought have said to add water to the perimeter of the house. Your explanations and advice make much more sense for a long term solution. Do any of your team work in Adelaide?

Hi Matthew
Could you please send me some names of engineers that you know and trust in Adelaide as well, I just bought a house and one side sunk and multiple crack on the side paving around the house
Thank you so much

Hi there,

Thanks for such a detail information about slab heave. I believe my house is also suffering from slab heave. Do you have any contacts in Melbourne

Hi Matt,

I am having the similar slab heave issue. Do you have anyone in Melbourne whom I can contact?


Have a house on a slab in the bag it has concrete blocks sitting on the slab but the slab has broke away under the wall and the wall has bowed out can that be fixed

Hi Matt

I got problem with sidewalk movement and heave around my house. I do not know where to start. Do you have anyone in Melbourne?

Appreciate the advice and info here. Do you have any contacts in Melbourne you could recommend to us? There is land sloping toward our house and it gets quite wet against the base of the house.

Could you please email me the details of a good structural engineer in Melbourne? I’m having brickwork movement issues and don’t know where to start!

We are experiencing slab heave in our 20 year old house in
Geelong, Victoria. Can you please recommend an engineer who would be able to help us. Your assistance is greatly appreciated. Your website is most informative.

Thanks for providing such an informative website. Shame you aren’t in Melbourne. My house has a number of cracks in the walls and several cracks in the brickwork. Can you please send me a recommendation for an engineer in Melbourne?

Hi Matt,

I’m also in Melbourne and am after a quality structural engineer to assess my property. Do you mind please emailing me a list of people you recommend? I’m in the northern suburbs. Thanks

Hi Matt,

We’ve had a newly poured raft slab on soft sand. I noticed sand had fallen down around the steel mesh around the outside beam of the slab. After asking the builder to rectify before pouring I dug around post the pour to see exposed mesh/steel. Should we be concerned? What’s the remedy for a situation such is this?

Hi John
No, it’s not a good situation but neither is it the worst thing I’ve heard of.
The builder should fix the exposed reinforcement issue before any perimeter slabs are poured and the area becomes inaccessible.
I expect the solution would be to hand trowel a cementitious repair mortar in and around the steel reinforcement to reinstate the full concrete cover. As an extra precaution, it would not hurt to also paint the steel so that it cannot corrode.
The whole repair should be supervised or at very least specified by your builder’s engineer so that it is an authorized repair and the repair is covered by the engineer’s paperwork.
Matt Cornell

Matt, I discovered this conversation today while searching for answers to a similar problem and decided to write.

My 50-year-old house was built in 1971. It’s in a section of Mississippi where Yazoo clay is common.

In 1999, the house was leveled, and a French drain installed because water was underneath. Slab was adjusted again in 2007, with piers added. A 2nd French drain was installed in 2017 after ground on east end of house stayed wet, probably, from neighbor’s broken pipe.

Eventually, 2 windows broke, wall had cracks, floor seemed unlevel, an interior door would not close, and kitchen cabinets were pulling away from wall.

Eight foundation companies surveyed and offered possible solutions. Three people thought a French drain next to the footings would help solve the problem. Others didn’t make sense.

Two 2 hydrostatic plumbing tests found no leaks.
I chose a reputable foundation company and, with apprehension, had the THIRD French drain installed in June, 2021.

We have had very limited rainfall in the past many months. However, the heave is still active! A 3rd window popped in June and the 4th broke and fell out in Sept. Wall cracks and ceiling separations are larger. Of great concern are noticeable buckles on the roof and pops in the attic. Facia boards are separating from roof outside.

Man from foundation company said he had never seen anything like it–“it doesn’t make sense.” His engineer boss said to get soil tested and that’s all they had to offer!

I’ve located a soil consultant/engineer who can do a test. I’m not sure what can be done after the test to help the heave problem. He did mention possibility of putting chemicals in the ground to stop underground water flow! I hate to keep spending money with no results!!!

Other info that may or may not be related to the situation.
1. A large oak tree in the drain area (maybe 12-15 feet from house) was cut down several years ago.
2. After a rainfall, water runs underground from neighbor’s backyard and pours out of the expansion joint of my driveway. That also happened on a completely dry day when water was running in their backyard.

I’m at my wit’s end dealing with this and in fear of losing my house.
Any suggestions/advice you may offer will be welcomed.

Thank you,

Hi Gail
The soil test will tell you the reactivity of the soil – how much volume change can be expected as the moisture levels in the soil change. I guess it will tell you how hard you have to work to maintain consistent soil moisture conditions. Given the work you have done already, I would say you already know you have to keep the ground very moisture stable to stabilize the house.
Your success is going to depend on how well the French drains remove moisture from the ground. They tend to be terrible at removing water that is already in the ground because heavy clays hold onto moisture really well. it is sand and gravel that is porous and lets water straight through.
The other factor is the base of the French drains needs to be graded evenly towards the outlet point. There cannot be ups and downs or water will settle in the low points, ask into the ground and all the good work will be wasted.
So stabilization for you will look like keeping water away from the perimeter of the house by grading the ground away on all sides. If water can get in under the building then that should be handled by removing the obstacles that allow the water to drain away. Add spoon drains and swales to control water at the surface.
The other precaution is that since your house was re-leveled when the soil conditions were variable, it may mean that the house will be severely out of level when the soil moisture conditions stabilize. At this point, you will need to have the house re-leveled – and perhaps even while the ground moisture conditions stabilize.
You can try removing some of the internal posts under the house and strengthening the timber beams with steel beams – that way the grade of the floor is only affected by 2 places along any one beam instead of three places.
I hope your house gets the help it needs. Regular re-leveling may be your only chance.
Matt Cornell

Hello. We’ve had upward heave in our slab and, despite doing what you recommend on your site & following recommendations of a structural engineer, we’re still experiencing problems. Our house is on a fill-in slab and the house is over 20 yrs old. The previous owner hid signs of the movement when we bought and we don’t believe pursuing a legal claim is possible. Do you have any suggestions for who we should contact for assistance? We’re devastated at what has happened and feeing powerless to the continuing movement. We’re in Melbourne.

Hi Matt,
Can you please recommend a good engineer in Melbourne. All the cornices in my house are cracked and there a re few cracks in walls. Upon j veatigation last year it was found a drain underneath the house was broken so it was fixed but some cracks are still appearing. I want to make sure there is nothing g else going on.

I am having a slab heave issue in my newly built house ( 18 months old now ). I experienced the cracks, stiffed doors, lifted door frames (some doors lifted about an inch) cracks in the mortar, loud noise from the ceiling, and most of the issues within a few months after handover.

Reported to the builder from time to time initially he said to wait for 6 months and then again 6 months and keep dragging till today.

The site is P and H2 class and the builder did not install AGI drain and silt pt around the house, which is clearly mentioned in the soil report that his site requires a proper drainage system which I got to know now.

Before the construction, he first included the AGI and silt pit in the plans and charged me but later he removed saying agi drain and silt pit is not required and credited back and now when the damage is done the builder is saying me to install AGI

He is using all sorts of excuses saying water ingress is causing this…

I installed the concreting parameter immediately after handover.

May I please know – who is responsible to install the drain. It was his decision to remove it from the plan and now asking me to install .


Our house is approximately 20 years old , we are having a heaving problem, do you know any engineers in the DFW area to help us?

i have read your site and found what I was looking for. We have all of the issues. We had one previous company that “repaired” an underground garage wall, but they caused other issues. We live in the U.S. and wondered if you have trusted associates here that you could recommend. We need an engineer to check out our problem foundation and advise if they can fix it.

Your help is greatly appreciated.
Bonnie O’Hara

Hi Bonnie
I’m glad we were able to help. Unfortunately, I don’t know any engineers in your area but I know someone who might. I’ve sent you an email. I hope you get your house problems sorted.
Matt Cornell
Cornell Engineers

Hi Justin
I’m sorry but I don’t know any slab heave engineers in Sydney. I wish I did because I get asked this quite regularly. You’ll need to Google to find a qualified structural engineer experienced with slab design to AS2870 and experience in recording site levels, giving evidence in court and supervising remediation work.

Hi Matthew,
Any chance you have a recommendation for someone in Vancouver BC (Canada) who can help me with slab heave and concrete improvement (cracks, spralling, etc). Many thanks for this article & your advice!

I might well have someone you can try. I’ll drop you an email.
Matt Cornell

Hi Matt, the majority of builders seem to be using Waffle Pod slabs nowadays as opposed to Raft slabs.

Our current house is on a raft slab on class H soil and as we are vaguely considering a new house in our local area, I am loathe to get one built with a waffle pod. I find it somewhat disturbing having chunks of polystyrene under my slab rather than nice firm sand, as in a raft slab.

Anyway, can you offer any perspective on the two slab styles? Which would you use for your own house?

We have heaving and sinking happening at our house. We are on a perimeter foundation with peer pads. The peer pads are what are sinking and heaving. So far the perimeter foundation isn’t moving. We’ve had Ram Jack, Terra Ferma, and a soils engineer out with not a word of advice. HELP!!!! Cracked walls, doors that wont open or close, gaps in between the ceiling and walls and floors and trim. We need an engineer to help with creating something stable for the house to sit on, in its center.

Hi Amy, curious since this is an old thread if you have found any solutions? We too are having all of these issues and I am at my wits end.

Just wondering if a slab can heave in the middle from the front of the house dipping. I have a thin rectangle slab that is heaving upward around 40-50mm in the middle based on surveys which seems to be splitting the house in half. The front corner has dipped on one side close to the same amount.
We’ve checked the pipes which run parallel and perpendicular to the cracking under the slab and only found a root in a joint in the kitchen on the other end of the house from the damage. Static fill tests show water leaving the system but the builder says this has to do with the drains in the wet areas. We can’t find any significant cracks in the pipes but all the joints have lots of burrs.
The builder is saying it is caused by the surrounding pavers not having sufficient falls but there is no damage at the back of the house and rain barely gets down the side most times and the ground under the pavers isn’t excessively wet.
The ground under the slab on the side of the house the laundry and kitchen are on is soaked, highly reactive clay though the area under the highest point in the house on the other side seems dry. Could water leak from the dodgey kitchen joint and pool in the middle without causing damage in the kitchen? Could water from outside the slab cause something like this?
There is also a 500mm deep sand trench directly under the footing on the dry side which I don’t think should be there, especially on highly reactive clay. Just wondering what you think – I’m also worried it’s getting to a point if no repair.

Hi Maggie and Rochelle. I’ve been following with interest the conversation you’ve been having regarding your problems with slab heave. Thank you also to Jason for contributing. Maggie you are right – it is a very stressful time. Solving slab heave is a slow process. Rochelle, try to stay positive. Staying informed and asking lots of questions will definitely help you stay in control. The QBCC is very good at solving slab heave issues and the panel engineers are all very experienced. If you’d like to have a chat about your progress, my details are on the website.

Rochelle, do you have an engineer’s Construction Report that you signed, along with the building Contract as I did? These hold a lot of information useful to you. Under planning approval here in SA adjacent properties are not allowed to discharge stormwater onto neighbouring properties during construction or afterwards, I believe. I have had issues with my home since 2010 and still ongoing, although I have made some progress. I hope QBCC are able to assist and help you find solutions. Please look after your health at this stressful time.

Rochelle, although council did not approve my dwelling as a private certifier was used, they were concerned enough to get involved and this prompted my builder to repair the skirting, 24 wall cracks and sticking doors which appeared within the first year of build and they also rebuilt my non-compliant en-suite shower. Have you approached your local council yet? I was also able to access relevant BCA ‘Building Code of Australia’ at the council’s office which shows the building standards (albeit minimum) and a great tool with which to get your head around re your builder’s compliancy (or lack of). In SA there is a five year statutory warranty – you should also check your building contract and engineer’s report if possible for any breach of contract from the builder. These are SA conditions – yours may be different but bound to carry more weight in looking after the consumer.

Hi Maggie,
Got hold of the structural engineers report late this afternoon after trench digging had begun on both sides of my home.

Builders are not following the recommendations and not hearing my concerns. I have compiled a complaint file for our QBCC – 70 pages in total of information, contract, emails, photographs and have it ready to go.

The engineers report states edge slab heave due to poor drainage in highly reactive clay soil, lack of drainage in adjacent properties. Recommending immediate drainage at 50mm over first meter from home and then continued fall. Non-replacement of current pebbles recommended.

The builders have dug trenches and installed drains but are not following fall recommendations and are returning the pebbles.

I’m at my end. This is my new home, 8 months old and a massive investment. Due to their poor design, poor drainage around waffle slab and smaller than industry standard drains on both my property and that of my adjacent neighbours my house is no longer straight or I believe sellable in this condition.

I need help and hoping the QBCC can be of urgent assistance.

Thanks for getting back to me.

Hi Matt,

Bought my new home already completed and settled in December 2015. Moved in on 17th December and started noticing cracks and sticking doors in January 2016.

My home is 8 months old built on a waffle pod on reactive clay. House occupies most of our small 370m2 block. Numerous cracks in ceilings, cornices, walls, skirts lifted from floors, doors failing to open, Windows moving, fluorescing of bricks, moss growing up side of bricks, cracked mortar, cracked pathways and corners of garage.

Structural engineer paid for by Villaworld. Refusing to let me see a copy. Insisting built to industry standard and council approved. Minor cracks replastered when I mentioned reporting to QBCC and now re-openining 3 weeks later. Terrible noises can be heard at night. Slab heave mentioned and poor drainage as issue by builder representative this week. Builder proposing to put drains around house and replace current pebbles over the top as their way of fixing the solution. Structural engineer recommended verbally that pebbles were not recommended at time be attended to view the home. When I questioned the builder this week he said it was only the Structural engineers opinion they would do what they thought was necessary and I would not be living in it if not approved by Council in the first place. Having difficulty liaising with builders and only have one number I can call at Head Office on Gold Coast.

Submitted complaint against defective build to QBCC. Very concerned as home is only 8 months old that this is not a solution and being intentionally mislead by builder.

Any advice – is it time to engage legal representation?

I am speaking from down in Victoria, Matt Cornell will be more familiar with the Queensland situation and QBCC.My next move would be getting a independent report done maybe Matt’s company and getting together all the information about your built you can, especially photos while waiting for QBCC.Floor levels done now will be of great importance and show the degree of movement and whether the movement is on going in the future

Hi Rochelle
Queensland has gone from severe drought to extreme wet these are slab heave conditions.
I would engage your own geotech to supply you with a comprehensive report.Slab floor levels will indicate the movement of you slab and must be part of your commissioned report.
Considering the short time frame after construction to the emergence of damage , poor site drainage during construction would be a concern.Photos of the site during construction would be of great value if you consider taking the matter further.If you can show the builder didn’t create proper drainage conditions and did not use temporary downpipes during construction then this may be cause for legal action against your builder.
Gravels around your perimeter allow water in but stop evaporation and can great add to moisture levels.
Did the builder put the gravels down or grade the ground away from the footings?

Thanks for your good advice Jason. The paved pathway around the house has a good fall and a PVC barrier plus waterproofing compound has been applied to the slab perimeter. On the NE side where the slab heave began, a slotted ag pipe covered with bio cloth sleeve (encased with plenty of gravel) runs beneath the edge of the paving alongside a garden border that needs minimal watering.
Despite these measures there is still spalling with efflorescence along the slab edge on this side. Professional advice has suggested moisture is coming from ‘somewhere’ and perhaps a spoon drain may help? I am not convinced this will be a solution if there is an underlying problem to resolve.

Thank you Jason for your advice. Sadly a return verandah would be out of the question and the small front entrance porch is thankfully only a problem when rain and prevailing winds drive the moisture in (which is fairly infrequent). I have purchased the tiles in readiness for the contractor to lay, for when he is available. I do have a question though please; would it work if I removed paving from around the perimeter and replaced it with gravel, as a border against the remaining width of the paving? At the moment the paving is 1100 cm wide. I have to get my head around it looking odd perhaps, or it may just look planned?

Replacing paving with gravel on a flat or reverse slope area is probably the worst thing you could do. The gravels allow moisture from rain in but restrict evaporation, therefore, increasing the overall moisture around the edge of your slab. I have seen clay beneath gravel landscaping become saturated. It’s the same principle behind mulching your garden
it will definitely increase the moisture level.
The only exception to this is if you have a plastic barrier below the gravel that slopes away from the house and is puncture-proof.
Builders’ plastic can be used but it must run the water away from the house preferably into an agi drain or stormwater system.
Covering the area with plastic will of course slow down the drying of the wet clay.
Grading the ground level away from the house is what is recommended at the start of construction but is rarely done.
It is very difficult to do this post-construction but if it is feasible
to do this in your situation then I would consider that method.

Jason – not sure if I can answer your question re shrink/swell test as my private contractor (using Atterberg limits) shows material test report as Liquid Limit – sample air dried and dry sieved 68% result. The E-D classification was confirmed by three separate engineers ranging from 70mm (builder) to 110/115mm by another builder and geotechnical engineer.
The remedial work carried out has been slab edge waterproofing (which still needs monitoring as it is fretting) and waterproofing en suite shower. Garage rebate has also been waterproofed. Front porch still to be relaid due wrong alignment for drainage and the interior doors swing due heave.

Maggie- Atterbergs can really be compared to other Atterberg tests and not put into a ground movement calculation but by the sounds of it you have enough consensus to say the site was misclassified anyway.
The porch needs urgent re alignment as we may be heading into another wet period and any heave associated with incorrectly sloping paving may get worse.
One of the best ways I have experienced to improve soil heave is have the perimeter around the house covered (pergola/varandah) but the soil below exposed.This protects against weather but allows evaporation to dry the soil.Of course this is not always practical but it may get you thinking along this line and coming up with ideas to improve your own specific situations.

Jason, the slab was laid Dec 2009 – handover Jul 2010. Perimeter paved Aug 2010. It was perceived that surface water pooling at NE corner during construction (where heave is prominent) caused the heave but the builder said it was owner’s responsibility, re surface water, during construction. I still dispute this. The slab was designed for 70 Ys movement but my private bore log report showed 110 Ys. There is currently slab edge dampness despite remedial work in waterproofing same.

Maggie Unfortunately 2009 was the worst year for slab heave as that was the height of the drought and was followed by two
of the wettest years,the fall out we are still dealing with.
You said your slab is a E-D which is designed to handle in excess of 75mm but you also said the slab is design for 70mm which is a H2. Was that E-D determined after your own investigation and was that done with a shrink swell test?.
And what was the remediation work done ?

Thank you Jason (and Matt) for your comments. 24 wall cracks were repaired by builder in July 2013 and have held thus far. I have to accept the slab heave and 127 delaminated interior tiles because I settled out of court with builder on other issues.

I am hoping the slab continues to stabilize as the last levels survey suggested.

There is some evidence that between 4-6 years after slab heave occurs the slab will begin to stabilise.This doesn’t mean returning
to the original level but minimal seasonal movement.
E-D is a very strong slab and will resist returning back to anywhere near it’s original level.
If the source of excess water is removed then stabilisation could begin .Proper landscaping will help the soil moisture levels.Was your house built before 2010?

Hi Maggie
AS2870 states the design goal is no more than 30mm differential movement but this is a design aim not a requirement.
Damage(cracks) that exceeds the standards expectation is a more compelling case against a builder but the legal argument is continuing.

Hi Matt,
Great website, appreciate the conversation.
I’ve found I have a broad high spot emerging in a slab near a bathroom (brick veneer slab on ground, reactive soils), resulting various small cracks and a stuck internal door etc (estimate approx 35mm) – this high spot tapers down less severe across the whole house and sharply back down to the base of a load bearing wall across the room to the back (perhaps that wall / roof weight is holding it down more?). The high spot / cracks/ stuck door became most severe when it was a long dry spell in weather.

There is no pressure water lines under the slab. Therefore, I intend to get the sewer line servicing this nearby bathroom pressure tested as it seems to be almost under the highest point. Otherwise, could it be general waterproofing failure in the tiled base of the shower (although I think this is less likely and would show other signs)? In the meantime I have stopped using this bathroom.

I read your page about the ‘tea towel’ bowl experiment – based on this, would it be fair to say it may take a very long time to notice this swell dry out after the pipe is no longer used or repaired – perhaps weeks, months, or years? I’m hoping the door becomes ‘unstuck’ as my indicator that it is recovering, or might it never go back down?

Should that reveal nothing, then I guess will have to look outside for sources of other moisture drawing in under the slab in that location (it is near a concave L shape corner), and will then also look to improve drainage and concrete a path around the house perimeter (although I am unsure about how to finish concrete against the ‘charged system’ of downpipes to seal it off but still allow for movement).


Hi Nathan. It sounds like you have got some great ideas for solving your house movement problem. Great work. Yes, the timeframe for reversing soil moisture related movement is normally six to twelve months. A set of floor levels will help you monitor the movement as will crack width and sticking doors to a lesser extent. Fixing pipes is my favourite first step along with fixing site drainage. The effec of current and previously removed trees, consolidation of soft fill should be considered and ruled out if possible too. Finally you have the option of improving the building’s tolerance to movement by adding control joints in walls and ceilings. Best of luck solving you house movement issues. If none of your trials work out, at least you have ruled out some common problems before you engage a forensic engineer.
Matt Cornell

Hi Nathan

You could engage a forensic plumber to either flood test the sewer pipe or perform a camera inspection to determine if the pipe is failing.If it is failing and is not dramatically broken then re lining is a good solution and can be done externally.
As far as the slab returning to the original level this is unlikely
as the reo in the slab may be bend.Recent experience with a similar situation involving a pipe broken under the slab in highly reactive clay has not returned after several years.
The solution was to screed the floor not completely level but
enough to reduce the uneven feeling when walking over the heave spot.
This type of slab movement is unusual and involves a very localised lifting and often doesn’t involve the external load bearing wall heaving.
If the source of water was external and making it’s way under the slab then in most cases the heave would be first noticeable at the perimeter wall with the slab at the wall being the highest point.This doesn’t sound like your situation.
First identify the source of water ingress(possible pipe)
Then screed level with the possibility of minor localised grinding of the slab first but you must be careful not to get to close to the slab mesh.

Hi Matt,
We recently built a new home and there are horizontal and diagonal cracks in nearly every room of our home mainly in the joints and around doors between 2-3mm in thickness with the longest one running about 1m. The builder’s structural engineer came and said it is because the concreter has laid a concrete perimeter around our home with no slope. The was laid about 4 months ago and is level or slopping towards trench drains which apparently do no have end caps. Can 4 months of lets say incorrectly laid concrete cause this many cracks. We are in Melbourne at although we have had rain these past few weeks it hasn’t been pouring down.
I am not sure if the builder is trying to just put the blame on the concreter or would there be other underlying factors I should be looking at?

Dear Jennifer
Thanks for your question. Although I haven’t been involved in investigating cracks in such a young house, I would imagine that it is entirely possible that slab movement could occur that quickly. To protect your interests it might be time to engage an engineer to do some independent investigations including:
– a soil test to confirm the original site classification.
– an independent assessment of the original engineer’s design.
– a review of the site inspections carried out during construction.
– recording of floor levels and crack widths as a datum for future movement.
– a review of the weather patterns in the four months before and after your slab was poured.
– a look at historic aerial photos to see if your house is built over any natural features such as trees or creeks or dams.
– a plumbing test to see if your pipes are leaking or have been affected.
– measurements if the as- constructed slab beam depth and slab thickness
These investigations are fairly normal work for an independent investigation into house movement. It sounds like an experienced forensic engineer might be your next step.
Matt Cornell

Thanks, Matt. I have reviewed photos of our construction and have come across that our builder did not put any temporary downpipes down nor grade the slope of the perimeter of our slab as required in the engineering drawings as we are on ‘P’ class soil. Reading your advice about not engaging in lawyers and trying to come to a resolution with the builders first, what can the builder really do to rectify this though? Won’t the soil under our slab just keep moving for years to come?

Hi Jennifer
Definitely reverse or flat perimeter concrete can cause slab heave even with very little rainfall.The water saturates the clay
directly near your footing and the path doesn’t allow it to evaporate so the moisture level rises and the clay swells.
You may have a case against the concreter who constructed your pavement.
You first need to determine the cause independently with a geotechnical engineer.
What suburb are you in and how old is your house?

Hi Matt,
A few years ago we had a sinkhole open up in our backyard (approx. 1m deep).
After calling a plumber he told us it was a problem with the council’s pipes behind our property. I notified the council and they rectified a number of problems in the park directly behind us. You can physically see ground shrinkage in the backyard caused by the problem.
Since then we have developed cracks on our walls, and ceiling and I’m concerned about the slab movement as our gutter run is now leaning the wrong way.
I have a waffle Pod Slab and we were given a 20-year warranty on it (1 Year remaining).
Can you suggest what I should do moving forward because in my eyes the problem either lies with our council or Metricon?
Am I correct and what should I do moving forward?
Any advice you could give would be greatly appreciated.


Hi Scott
It would be worth having an engineer inspect your property, take levels, record damage and prepare a report.
There are a number of issues that can cause movement in a house. The report will help you identify and eliminate the issues that can be fixed. If the council pipe is one of them then I imagine you could use the report to start negotiations with council.
Matt Cornell

Hi Matt,

Myself and my neighbour have homes built on a waffle slab. Slab construction in 2004. Nothing happened in my house for 6 years, although my neighbour had cracks and leaks. In the past 4 years my house has cracks in the centre wall between 2 buildings and the east facing wall which backs on to units with garden beds next to the dividing wall and slab.
I recently took action in VCAT to avoid bring statute barred against the builder. The inspection I had done uncovered slab heaving although no crack is bigger than 3mm. Also uncovered were RLs which were some 900ml lower at the front of the house than the back. At mediation the builder blamed the engineer as he followed his advice. Also he agreed to install an agricultural drain down one side of the house and make good all the cracks.

Should I have settled my action and be satisfied that after 11 years some wall (internal and external) cracks and ceiling cracks is all that is arisen? There is no problem with doors, windows etc.

Hi Rodney
It’s never very satisfying to see cracks in your house – but I think it’s worse when the cracks reappear straight after you have then repaired.
After 11 years I’d expect your home would be due for some maintenance, repainting etc and this would be your opportunity to have any damage repaired and painted over. However if the house is still moving the cracks are likely to reappear.
Therefore you are right to have movement that has occurred after 6 years of good performance investigated. Maybe something has changed in the ground moisture regime under your building? Normally solving this issue will get your house back to a good level of performance.
You’ll already be aware that footing designs to current Australian standards are meant to offer a reasonably low risk of large cracks and a medium risk of hairline cracks. Whether you should be satisfied with these limits lies with personal perception of the cracks and where they appear. I’d focus on identifying and solving the issue that has caused your house to move after 6 years. Reverse that issue and get back to enjoying your house.
Best of Luck
Matt Cornell

Thank you Matt. The deviation is now 65 mm with further movement expected on this E-D site. Latest engineer’s report states home is structurally sound although I worry about further heave movement as in 2013 it was 58 mm and at that stage deemed to have reached 80% of the design parameter.

What is the maximum deviation of floor level tolerance to entire building footprint in SA please? My slab has heave of 58 mm and wondering whether SA has legislation similar to Vic and NSW tolerances where it is 20 mm.

Hi Matt

I have a townhouse that shares walls with 2 other houses (I’m in the middle). 3 years ago I noticed doors and windows sticking, cracks forming etc. I’ve had an engineer inspect and they’ve told me it is slab heave. Most likely because the air conditioners from my house and one of my neighbours house drain into the soil. My house is having more issues than the house next door. They’re cracks and doors sticking are not as severe so they haven’t bothered to try and figure out the cause. I’m not sure how to tell whether the problem is in my house or that their house is causing the issues. I know I will have to get more plumbing tests done. The CCTV camera footage showed no leaks, but a flood test has been recommended. Can you help guide me in the right direction?

Hi Natali
It’s good that you’ve had a cctv test of the plumbing, but when we assess a triplex unit like yours, we find there’s more value in assessing all three units at once (if possible). The shared footing system, if it is indeed foundation movement, is unlikely to only be having problems in one individual unit.
Just be careful though. Slab heave is often blamed by engineers and inspectors as an easy target. Did the engineer record floor levels and verify that the slab is higher where the water is entering the ground?
The other thing to watch is pre-existing conditions. What was where your unit is now before it was built? A dam? A drain? A stockpile of dirt? These prehistoric conditions could be contributing to the damage you are seeing.
Finally, arrange to get the original plans from the body corporate or from the council. That information will help the engineer confirm the footings were designed appropriately for the conditions that exist on the site.
Best of luck.
Matt Cornell – Cornell Engineers

Leave a Reply

Your email address will not be published. Required fields are marked *