A dormer facing the ocean on the shore of an island on the coast of Maine is exposed to some rough conditions: baking sun in summer, snow and ice in winter, and wind-driven sheets of rain pretty much year-round. And a dormer, of course, involves several tricky intersections between different roof and wall planes, clad with different materials. Making those complex intersections watertight is a head-scratcher. This July, JLC's Coastal Connection went up on the roof with Mark Pollard, lead carpenter for Thompson Johnson Woodworks on Peaks Island, Maine, to see how Pollard deals with the dormer flashing challenge.
The dormers shown here, part of the Cape roof of a house built in 2001, were experiencing water damage to sheathing, windows, and room interiors because of the intrusion of wind-blown rain. When the siding was stripped, Pollard found a collection of improper construction details, including reverse-lapped housewrap and flashing. The Thompson Johnson crew re-clad the dormers entirely, applying fresh Henry Blueskin vapor-open self-adhering housewrap and installing new windows. That story's coming up in the September JLC; for now, here's a detailed look at Pollard's flashing technique.
In a previous JLC article, contractor Kyle Diamond, of Millbrook, N.Y., demonstrated his method for making dormer flashing with soldered copper (see: "Best-Practice Apron Flashing," JLC 3/15). Pollard's method is similar—but instead of using soldered copper, Pollard uses coated aluminum coil stock, and seals the seams from the back using Zip tape. In this photo series, Pollard creates one corner flashing where the front of the dormer sits on the lower roof, and another that wraps around from the upper roof and side of the dormer to the front. Take a look.