Slab on grade foundations are foundations made from a slab of concrete. The concrete is formed into shape using a mould which is laid in the ground. The concrete is poured into the mould leaving no gaps between the ground and the foundation.

Slab on grade foundations are commonly used in warm countries. This is as they can be prone to the affects of freezing which can damage the structure. Likewise they are also practical in warmer countries where people don’t have under floor heating and have more room for this kind of foundation. They are also popular in warmer climates where people have problems with termites as the foundation has no gaps and has no wood in its construction so there is no risk of infestation.

Depending on the geographical location of the property slab on grade foundations may not be suitable. Slab on grade foundations can be used in countries with lower climates. However you may find it difficult to warm your property as cold air travels up from low ground temperatures. This can be reduced by installing insulation with the foundation. Just add an insulating layer to the mould before pouring in the concrete. Alternatively you can use heating systems set into the concrete slab such as hydronic heating. If you live in an area close to a floodplain the foundations may also be at risk of excess moisture.

You may also be limited if you wish to carry out extensive work on your property. Extending or restructuring your property will be much more labour intensive. You will also be restricting the access to utility lines which could cause problems with access in an emergency. You will also need to be careful when choosing materials for piping for utilities. Copper is commonly used for gas and water supplies but can soon perish due to a reaction with composites of the concrete. To avoid this, lengths of copper piping need to be lagged and fed through a conduit or alternatively plumbed above the slab. If you are running electrical conduits through the slab you need to take care to ensure they are water tight as moisture around the ground level can damage them and stop them from functioning.

Over time you may develop subsidence issues as the ground shifts. These can also be difficult to fix as the foundation cannot be repositioned. You can minimise the risk of subsidence issues by making sure that the earth below the foundation is properly compacted before laying the foundation.

Slab on grade foundations are well suited to areas with expansive soil types like clay soil. Elevated slab foundations perform well on clay soils but generally slab on grade systems are more cost effective for a variety of house designs.