Should You Put Plastic Under Concrete?

Thanks! Plastic is a moisture barrier generally to stop ingress from beneath the slab. If this is outdoor in an exposed area it probably doesn’t matter. I’d probably use plastic if the area is moist with little sun, just to alleviate any algae growth.

Join our #StructuralWhyFile to find out why you need a vapour barrier under a concrete slab in Australia. The requirements to have a vapour barrier under a concrete slab come from the NCC – the National Construction Code and the Australian standard AS2870 for residential footings and slabs. A vapour barrier is required under a concrete slab for a Class 1 building and for Class 10 where the slab is continuous with the dwelling. Most professional shed slab builders will install a polyethylene membrane under a shed concrete slab even if it is not specified.