Redundant waterproof layers create airtight and watertight protection for the windowsill.
Mark Pollard and Tyler Stroud apply Grace Ice and Water Shield to the rough windowsill, lapping the sticking membrane onto the top course of roof shingles on the roof below the dormer, to protect the framing from the driving rain of ocean storms.
At the intersection of the sill and jack, Pollard applies cut pieces of ZIP flashing to seal corners.
Pollard applies a custom-bent piece of aluminum coil flashing to the window opening base. The flashing extends down the dormer face and onto the roofing shingles below.
Stroud sets shingles onto the prepared opening to create a drainage slope under the window unit. He lays the shingles into a bead of silicone caulking for a better water and air seal.
Before applying Henry Blueskin WB25 window flashing to the shingles, Pollard primes the wood with Henry Spray Prep primer as recommended in the manufacturer's literature.
Stroud (left) and Pollard apply the WB25 membrane to the sill. WB25 is vapor-closed, waterproof, and airtight.
Pollard fits and smooths the WB25 membrane onto the sill, lapping down onto the site-bent aluminum flashing. WB25 is a peel-and-stick product, but Pollard has observed that it only adheres well when the company's recommended primer is sprayed on before the sticky membrane is placed.
Pollard places a corner patch over the small gap in the membrane at the window rough opening corner. Note: when multiple layers of Henry WB25 sill flashing are lapped in this fashion, Henry primer should be sprayed onto the lower piece and allowed to dry before the upper patch piece is placed.