Does a raft slab need a vapour barrier the same way a waffle slab does?

Yes — a vapour barrier is a genuinely standard requirement under a raft slab too, managing ground moisture the same way it does under any other slab-on-ground system.

The detailing differs slightly given a raft’s largely solid underside compared to a waffle slab’s void, but the underlying compliance requirement is genuinely the same.

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