Does a waffle slab need a vapour barrier?

Yes, typically — a vapour barrier (a plastic membrane laid before pouring) is standard practice under a waffle slab, helping manage moisture movement from the ground into the slab and, ultimately, your home.

This is a genuine, standard part of correct waffle slab construction, not an optional upgrade — properly managing ground moisture is important for both the slab’s long-term performance and what’s built above it.

Your builder or contractor includes this as a standard part of correctly executed waffle slab construction, following established best practice rather than treating it as a discretionary add-on.

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