When installing poly underlayment, the edge overlap should be how much?

When installing poly underlayment, the edge overlap should be how much?

• A. 2 inches
• B. No overlap
• C. 6 inches
• D. 12 inches

Answer: (C)

The key idea is creating a weatherproof seam by giving the edges of poly underlayment a proper overlap. Overlaps help water shed over the seam and stay covered even if the material shifts a bit or there’s wind uplift. Six inches is a standard, recommended overlap because it provides enough coverage to seal the seam reliably without wasting excess material. A smaller overlap, like a couple of inches, could leave gaps that let moisture through; no overlap would be ineffective, and a 12-inch overlap is typically more than needed and wastes material. Always follow the manufacturer’s guidance, but six inches is the common, tested practice.

The key idea is creating a weatherproof seam by giving the edges of poly underlayment a proper overlap. Overlaps help water shed over the seam and stay covered even if the material shifts a bit or there’s wind uplift. Six inches is a standard, recommended overlap because it provides enough coverage to seal the seam reliably without wasting excess material. A smaller overlap, like a couple of inches, could leave gaps that let moisture through; no overlap would be ineffective, and a 12-inch overlap is typically more than needed and wastes material. Always follow the manufacturer’s guidance, but six inches is the common, tested practice.