Flashing cantilevered joists

Q: I am starting to build a house that has a small second-story deck. This deck will have 4x6 floor joists that cantilever from the interior floor joists through the siding. The deck will extend from the side of the building with no posts to hold it up. It looks great, but how do I flash where these cantilevered joists exit the wall?

A: Contributing editor Mike Guertin, a builder in East Greenwich, Rhode Island, replies: It’s a two-step process done at the time the siding is installed. Wrap the wall beneath and between the joists with housewrap, leaving about 2 in. of sheathing exposed on each side of the joists. Don’t bother with housewrap above the joists at this point, or if you do, let it overlap the tops of the joists by about 6 in. Then tack up the bottom 12 in. of housewrap to expose the sheathing. Bring the siding (presuming that you are using lap siding or shingles) to a point just below the joists.

Then flash the joists using flexible flashing tapes such as Tyvec Flexwrap or ProtectoWrap Flex Tape. These tapes can be wrapped easily around the joist, starting by wrapping the lower piece around the bottom of the joist and a bit more than halfway up each side. Lap the flashing tape over the top of the siding so that any water that gets down to the flashing tape will be directed to the surface of the siding. The next piece of flashing tape then wraps around the top of the joist and down the sides to lap the bottom of the joist.

Finish up by bending and soldering a copper flashing as shown in the drawing.