If water is entering the home through the ceiling near a chimney, one of the prime suspects is often the chimney flashing. Flashing is the sheet metal that keeps the intersection between the chimney and roof watertight. It comes in different types, depending on the design of the chimney and homeowner preference, but it is generally made of two layers of overlapping metal plates.
These plates form a double-layered “skirt” around the base of the chimney so there is no joint there where water can leak in. One layer sticks up from the roof, and the other layer hangs down from the chimney, draping over the first layer. In this way, the chimney can expand and contract with heat from a fire without damaging the flashing or the roof. The outer layer of flashing is called the counter flashing. The lower, inner layer of flashing is called the base flashing.
The top of the counter flashing is sunk into the mortar joint between two bricks in the chimney and then bent downward at a 90 degree angle. This joint is then usually sealed with caulk. The joints between the separate plates are also caulked.
Over time, flashing degrades. It can rust, deform, or pull away from the chimney or the house. Sometimes damaged flashing is repaired with caulk or tar. These products may temporarily stop leaks, but they do not expand and contract at the same rate as the chimney or the roof, and eventually crack and pull away, usually within only a year or two. A product called “FlashSeal”, which consists of a flexible sealant plus a fabric layer, is available which will last somewhat longer. In cases of extreme flashing deterioration, you may wish to install new flashing, which lasts longest of al
Barnhill Chimney installs only copper flashing. Copper chimney flashing is the most durable type of flashing, with the longest service life. Properly maintained and serviced, it can last the life of your roof. It also has the advantage of being solderable, for a watertight seal. Copper can also be embedded in fresh mortar and won’t degrade, even in mortar that’s continuously saturated. Our flashing is custom made for your chimney out of 16 oz. sheet copper, and comes with a 15-year warranty.