What is Chimney Flashing

Chimney Flashing Creates a Seal between the Chimney and Roof to Prevent Leaks

By Mark J. Donovan

If you look closely at a where a chimney abuts a roof you will notice stepped metal climbing up from the roof and onto the chimney wall. That metal is referred to as chimney flashing and it is used to create a leak free seal between the chimney and the shingled roof.

Chimney flashing is installed when the roof is shingled. Chimney flashing consists of small sheets of metal that are formed and interwoven underneath the shingles near the chimney and slightly up the side of the chimney. To attach the chimney flashing to the chimney brick mortar properly the brick mortar is removed and the chimney flashing is slid into the seam and slightly up the back side of the chimney wall. Finally the chimney flashing seams are cemented and a bead of polyurethane caulk is applied to seal the flashing into the brick mortar seam.

Chimney flashing is available in a variety of metals including lead, copper, tin coated steel, and galvanized steel, and sometimes aluminum (however aluminum should not be used). All of the metals, with the exception of aluminum, can easily be soldered, brazed, or welded to create leak free seams. They are also used due to their ability to be easily formed to the contours of the roof and chimney wall.

See my Asphalt Roofing Bid Sheet if you are looking to have your roof reshingled and the chimney flashed.