The balcony I’m repairing has cantilevered joists extending into the framing. The siding and some of the wall sheathing around the joists have decayed. I’m afraid the rot may extend into the floor blocking and perhaps beneath. I can deal with the structural repairs, but what is the best way to flash the balcony joists to prevent water leaks? All the original builder did was caulk between the siding and the joists.
—Daniel T. Browning
Essex, Conn.

Mike Guertin: Replace the housewrap in the area around the cantilevered joist, and lap it in with existing housewrap above and below the area you expose. Flexible flashing tape such as DuPont Flex Wrap is the best solution I’ve found for cantilevered joists. For each joist, cut two strips of the flashing tape about 5 in. wide with a length that is three-quarters the perimeter of the joist.

Score through the backing about 2 in. from one side with a sharp knife, and then remove the backing. Bond the 2-in. strip of exposed adhesive down one side of the joist, across the bottom, and up the other side. Remove the remaining 3-in. strip of backing, and flare the flashing tape out over the housewrap.

Cut a 3-in. head flap in the housewrap at the top of the joist (similar to a window head flap), and fold it up. Prepare another strip of flashing tape by scoring and removing a 2-in. strip of backing. For the top of the joist, bond the strip to the joist, overlapping the previous piece. Again, remove the remaining backing, and flare the tape over the housewrap. Finally, fold the head flap down, and tape over the slits with small pieces of flashing tape.

Most flashing tapes can’t be left exposed to UV rays. Even though the decking will block most sunlight, it’s safer to cover the exposed flashing tape that wraps the joist, so cut and wrap a 21⁄2-in.-wide strip of plastic or metal flashing all the way around the joist to cover the tape. Then install the siding around the joist as normal.