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Vapor barrier (under slab)
A vapor barrier is a plastic sheet under a slab that helps block ground moisture from moving into the concrete and into the home.
Why it matters
Moisture coming through a slab can ruin flooring, create odors, and feed mold.
Where people get this wrong
Concrete is not waterproof. It can transmit moisture. A torn vapor barrier is almost as bad as none in sensitive floor systems.
Real-world example
A basement smells damp even without visible water. Later, the flooring adhesive fails. A missing or damaged vapor barrier can be the root cause.
Where this hits your build
This matters during site work and foundation. Mistakes here get buried and are expensive to fix later. Pay attention before concrete is poured.
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