What is the required edge overlap for poly underlayment under a concrete slab?

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Study for the B3/61 Contractor Trade Exam. Boost your success with flashcards and multiple choice questions, each offering hints and explanations. Prepare to ace your test!

Multiple Choice

What is the required edge overlap for poly underlayment under a concrete slab?

Explanation:
When laying poly underlayment as a vapor barrier beneath a concrete slab, seams must be overlapped by six inches and sealed. This sufficient overlap ensures the barrier remains continuous and minimizes moisture transmission through joints. Butt edges would still leave gaps in the barrier, and overlaps of only half the sheet or just a couple of inches aren’t reliable for preventing moisture movement. Six inches is the standard requirement to maintain effective vapor protection under the slab.

When laying poly underlayment as a vapor barrier beneath a concrete slab, seams must be overlapped by six inches and sealed. This sufficient overlap ensures the barrier remains continuous and minimizes moisture transmission through joints. Butt edges would still leave gaps in the barrier, and overlaps of only half the sheet or just a couple of inches aren’t reliable for preventing moisture movement. Six inches is the standard requirement to maintain effective vapor protection under the slab.

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