Waffle slabs have become more popular with builders because of economics as a quick and cost-effective way of building a concrete slab on the ground.

Waffle slabs are constructed on an array of polystyrene blocks

Waffle slabs attract better energy ratings and are better for insulation, they are easy to setup and build, and are a fantastic solution for pierced suspended slabs on filled sites.

If your development is on appropriate founding soil close to the surface and is a relatively flat site, a waffle slab may end up being more energy efficient, use fewer materials, and cost less to build, in comparison to a traditional raft slab.

They are unsuitable for residential construction:

Excessive soil movement can lead to cracking and structural damage

If your site is classified as a reactive site, and is subject to high seasonal movements, a waffle slab may not be strong enough to bridge the gaps in local depressions that may occur.

Waffle slabs sit higher up in the ground than raft slabs and so they are less suitable for sloped sites where extensive levelling would need to take place first.

Sites that are prone to drainage issues around the slab may be subject to seasonal or occasional swelling which typical waffle slabs may not be strong enough to handle.

Waffle slabs use less concrete than raft slabs, the flip side is that they are not as good at acting as anchors for houses in high wind areas.

Builders Institute Trainers