Chimney Flashing Repair by Local Jacksonville Experts

Base flashing and counter flashing

The roof deck swells, shrinks and deflects, and the chimney stands on its own footing, so the joint between them is made in two layers of metal that overlap without being tied together. Base flashing, called step flashing on a shingle roof, is tied into the roofing and turns up the chimney. Chimney counter flashing is tied into the brick and turns down over it, so the roof can move while water still runs over the lap.

The Brick Industry Association's detail has the base flashing reach at least 4 inches along the roof and 4 inches up the face, with the counter flashing lapping it by at least 3 inches, tabs folded around each corner and every lap sealed. When that arrangement fails, a chimney flashing leak follows, and the lasting fix is to reflash the chimney.

Counter flashing set into the brick

Counter flashing pressed against the brick and held by a bead of caulk depends on that bead alone, and brick is rough enough for water to run behind it once the sealant ages. The BIA detail runs the counter flashing through the chimney wall. On a repair where the brick above stays, we saw a reglet into a mortar joint, bend the top edge of the new metal into it, wedge it tight and seal the slot, so the sealant is a backup.

Chimney reflashing instead of more tar

A tar patch or caulk bead over a failed joint can stop the drip for a while, then sunlight and movement break its bond. BIA Technical Note 19B says caulking is frequently used to hide poor workmanship, and where a detail does call for sealant it recommends polysulfide, butyl or silicone on a primed and backed joint. Old tar comes off first so the metal under it can be judged. When the flashing around the chimney needs repair, chimney reflashing with new metal is the lasting answer, and a full chimney flashing replacement is what we price when the old pieces cannot be reused.

Shingle, tile and metal roofs

On asphalt shingles, Florida Building Code, Residential R905.2.8.3 calls for the step-flashing method or a continuous L flashing at a sidewall, and R905.2.8.4 sends chimney flashing to the shingle maker's instructions: a bent piece woven under each course, an apron on the downslope face and a back pan on the uphill face, each fastened to the deck. R903.2 is the test for the finished joint, with no path for water into the wall or roof.

For clay and concrete tile, R905.3.8 calls for flashing and counterflashing per the tile maker's instructions and the FRSA/TRI Florida High Wind Concrete and Clay Roof Tile Installation Manual, and tiles around the chimney have to come up to reach it. Metal roofs follow the panel maker's curb and wall details, and on a low-slope membrane roof the membrane turns up the chimney under a metal counter flashing.

Flashing metal and the cricket

Table R903.2.1 sets minimum thicknesses for flashing metal, and the BIA's flashing brief ranks the options: copper, stainless steel Type 304, galvanized not recommended, and aluminum attacked by fresh mortar. Copper touching galvanized steel or aluminum in the wet sets up galvanic corrosion, so the metals and fasteners are matched.

FBC Residential R1003.20 requires a cricket where the chimney is wider than 30 inches parallel to the ridge and does not meet the ridgeline, flashed and counterflashed like the rest of the joint. Framing and roofing a cricket is separate work, and we name who builds it.

Where the roofer's work begins

Our job is the metal joint and the masonry it is set into, including the mortar joints along the flashing line. Roof covering beyond what has to be lifted, underlayment and rotted decking belong to a roofer, and a planned re-roof is the best time to replace chimney flashing. A leak without a clear flashing failure goes through chimney leak repair and its water testing first.

Not sure it is the flashing? Call (904) 920-5495 and book a free inspection.