- Q.What is the best way to detail the
connection of a pitched roof abutting a sidewall?
A.According to the National
Roofing Contractors Association, when the rake edge of a
pitched roof intersects a vertical wall, #15 felt should be
laid under the shingles, extending 3 to 4 inches up the
vertical wall. Metal step flashing (flashing shingles) should
be used, with one flashing shingle for each row of shingles.
The flashing shingle should be bent to extend under the asphalt
shingles on the roof about 2 inches, and 4 inches up the
vertical wall. Each metal shingle should be placed slightly
up-roof from the bottom edge of the asphalt shingle which
overlaps it. Nail the flashing shingle with one nail along the
upper end of the vertical leg, as shown in the
The siding should be brought down over the flashing shingle
to serve as a counterflashing, but cut the siding back a couple
of inches, far enough to permit painting the ends of the wood
siding. This will prevent water from wicking into the ends. If
vinyl or metal siding is used, the flashing should be sealed to
the sheathing with caulk or butyl tape. Vinyl and metal siding
are not waterproof, and water blowing through the joints can
run down the sheathing and behind the flashing.