How should roof flashing be installed on a brick wall?
Two pieces, two jobs
- Base flashing: step flashing along a sloped side wall, one piece per shingle course, or a continuous apron where the roof dies into the wall horizontally. It lies on the roof and turns up the brick at least 4 inches.
- Counterflashing: a separate piece anchored in the masonry that covers the top of the base flashing. Because the two are not fastened together, the roof and the wall can move independently without tearing anything.
How counterflashing gets into the brick
On an existing wall, the roofer grinds a slot, called a reglet, about three quarters of an inch to an inch deep into a mortar joint, inserts a bent lip on the counterflashing, wedges it tight and seals the joint. On a sloped wall the counterflashing is cut in steps that follow the brick courses. The lip belongs in the mortar, never in the brick face. The common bad version is a strip of metal fastened flat to the brick with a bead of caulk along the top, which depends entirely on sealant that cracks in Georgia sun.
The water you cannot see
Brick is porous. In a long soaking rain, water passes through the face and runs down the back of the brick. On brick veneer walls, through-wall flashing and weep holes, built in when the wall was laid, carry that water back out above the roof line. If they were never installed, the roof flashing can be perfect and the wall still leaks into the framing. A stain that appears a day after rain, or white salt deposits on the brick just above the roof, points to this problem.
Metal choice
Bare aluminum corrodes against wet mortar, so counterflashing in brick is usually coated aluminum, prepainted steel, copper or lead. See roof flashing explained and chimney leaks and crickets.