What is Slab Heave?
Slab heave is a result of uneven movement of a house footing and slab. Uneven changes in ground moisture can also lead to slab heave, where clay soils swell (and expand) when they become wet and shrink when they dry out.
Slab heave can resemble a dome – when the slab is higher in the middle than at the edges – or a dish, when the edges end up higher than the middle of the slab.
While not common, it is a serious problem and can be very costly to rectify, sometimes requiring legal intervention to determine who is liable for the cost.
What Causes Slab Heave?
Slabs can be built in a number of ways. One of these is known as a ‘waffle slab’.
A waffle pad is a concrete slab, usually 100mm plus thick, poured over polystyrene pads which form channels or beams. This is similar in principle to how conventional slabs used to be poured – however, in place of polystyrene pads, the area was built up with packed sand.
There is some debate over whether waffle slabs, as opposed to conventional slabs, can trigger slab heave. There is no substantial evidence in this regard.
Inevitably, slab heave can be attributed to the following factors:
Do I Have Slab Heave?
There are typical building and structural defects that will be apparent if slab heave exists. Expert advice will be required to assess the defects to determine the complexity of the issue.
Have you observed any of the following?
- Gaps under walls
- Damage to cornices
- Uneven floors/sinking or rising of your structure
- Doors and windows that won’t close properly
- Cracks in your brickwork
- Cracks in your internal walls
- Cracks in your floor and wall tiles
- Plumbing and pipe problems
- Cracked sewers and storm water pipes.
How Can I Avoid Slab Heave?
For the main part, water is your enemy when it comes to slab heave.
It’s important to keep an eye on any possible water damage around your home, especially during the cooler months. Often water drainage is overlooked until substantial heavy rain alerts you to a problem.
We recommend that you locate any potential water sources that are entering the ground around your home and eliminate them.
These may include:
- Fixing leaking pipes and dripping taps
- Ensuring that roof guttering is clear of debris such as leaf litter and silt. This will help prevent any water backing up and flowing back into roof spaces or under your home.
- Clearing the sub-floor of debris, removing any obstruction to the flow of ventilation to prevent any dampness from developing.
Check these issues first before speaking with your builder. You may then need to work with your builder to seek a resolution.
If you have noticed an issue and don’t know what to do next, call The Home Inspection Hub and organise a special purpose building inspection.
We can ascertain the cause and extent of the problem and give you some professional advice on the next steps to take.
Are you building a new home?
When building your new home, you can rely on our team to help you throughout the construction process. As registered builders, our new home inspectors specialise in reporting on construction projects.
We conduct a series of independent building inspections at each critical stage of your new house construction:
- Base Stage
- Frame Stage
- Fixing Stage
- Final Handover (PCI)
We recommend organising your base stage inspection prior to the concrete being poured, so that crucial items can be checked before they are concealed by concrete.
Items that we check at base stage include:
- the site conditions such as gradient, surface drainage, retaining walls and access
- orientation of the building and positioning of reinforcement starter bars
- damp-proofing membrane
- termite protection.
It is important to note that our reports do not cover any part of the building located beneath the ground surface.
We can give you professional advice and put your mind at rest.