Chimney Flashing Repair in Southfield, MI

Along the sides of the chimney, L-shaped step flashing pieces are laid one per shingle course, each one lapped over the one below, like the shingles themselves. Counter flashing then laps down over the top edge of the step flashing from the brick. The two aren't fastened to each other, so the chimney and the roof can move separately without tearing the seal. A front apron covers the downhill face. When a re-roof happens, the Michigan Residential Code says counter flashing that's rusted or damaged can't be reinstalled, so on an older chimney, expect new metal. Leaks from the sides show up as stains on the ceiling or wall next to the chimney.

The back of a chimney is a dam. Water and snow coming down the roof pile up against it. A cricket is a small peaked roof framed behind the chimney that splits the flow around both sides. Under the Michigan Residential Code, any chimney wider than 30 inches needs a cricket on its uphill side, covered in sheet metal or the same material as the roof. If yours is wide and leaks from the back in late winter, a missing cricket is the first suspect.

An uncapped flue is an open pipe that funnels rain straight down the inside of the chimney. The Chimney Safety Institute of America (CSIA) calls a cap the least expensive way to prevent water damage, and notes that a well-built cap keeps out birds too. The mesh sides also stop squirrels and raccoons from moving in. InterNACHI estimates metal caps at 10 to 20 years. HomeGuide puts chimney cap replacement at $200 to $850.

The crown is the slab on top of the brick that sheds water away from the flue. CSIA says most crowns are made of ordinary mortar, which doesn't stand up to years of weather. It recommends a Portland cement-based crown that overhangs every side by at least 2 inches, so water drips clear of the brick. InterNACHI gives a mortar cap about 15 years and a concrete one 100 or more. Hairline cracks can be sealed. A crown that's broken through or crumbling gets resurfaced or rebuilt, and that's mason's work, usually done before the new flashing goes on.

How counterflashing attaches to the brick decides how long it lasts. The durable way is a reglet: a saw cut into a mortar joint, with the top edge of the flashing bent in and sealed. The shortcut is surface-mounted flashing, held to the face of the brick with a bead of caulk along the top. When that caulk cracks, water runs behind the metal and straight into the roof. On a chimney with old tar patches, the roofer grinds out the joint and starts fresh. A stepped reglet that follows the mortar lines up the side of the chimney looks cleaner than one long diagonal cut.