Roofer Mike gets into the finer points of chimney flashing . As is the case with roof repair in general, the devil is in the details.
There are a lot of chimneys on South Florida homes, as counter-intuitive as it may seem. As a consequence they account for a significant number of roof repair calls in Miami. Like roof leaks in general, leaks around the chimney are almost always attributed to workmanship of the metal flashings. We advocate a total rebuild over fixating on the leak area which only invites future problems. Kinda’ like fixing a flat when all your tires are bald.
Complete Chimney Flashing Rebuild
We tear out everything on all four sides, right down to the wood deck. If necessary we install a “cricket”, a structural feature which transfers water from one area to another. By Code all chimneys more than 30” wide require a cricket to allow water to flow freely around it.
The chimney is treated the same as a complete roof replacement once all rotten wood has been replaced . The area is dried in with 30lb felt. By Code all metal flashings must be fabricated from 26 gauge galvanized sheet metal. Wall flashings must be a minimum 4” X 5” but we favor 5” X 7” for a bigger and better flash. Cutting and bending the metal while setting individual pieces in flashing cement as they are nailed in place requires precision.
Don’t Use Cheap Roofing Materials
We use top grade modified roof cement on all roof repairs and replacements. Regular roof cement dries out and shrinks faster. The flashings are then coated with asphalt primer to ensure good adhesion to the underlayment. It is truly amazing how many chimneys fail after 10 or 15 years because of cheap roof cement and/or the absence of primer. Note: When working within a half mile of salt water all flashings must be upgraded to aluminum, stainless steel or copper.
Stucco-stop flashes over the wall flashing and also requires a professional skill set, particularly when mitering corners. It is usually attached to the masonry with 1 1/4” drive pins and sealed with a thick bead of calk across the top. Chimneys built with stucco over wire mesh and plywood require cupped washer-screws. We see many of these caulk beads fail and cause leaks. So, we also apply caulk to the back side of the flange where it meets the wall to achieve a 100% seal. We exceed Code on this. We do not use cheap caulking from the big orange box, similar to our thinking about roof cement and materials in general.
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