Chimney Flashing

Chimney Flashing Repair and Re-Flashing

When your chimney has developed a leak you will usually notice water staining above the chimney when it rains. It will likely be on the ceiling and perhaps running down the wall as well. This indicates that the chimney flashing is allowing water in and needs to be re-flashed.

Chimney flashing is a construction detail used to seal and protect the joints between a building’s roof and chimney from water penetration. The joints created by the intersection of the roof and chimney are among the most vulnerable areas of roofing systems. They constantly expand and contract in response to changes in humidity, temperature and age. The greater the number of such projections, the greater the potential for serious leaks. Flashing is used at these intersections to keep rainwater from leaking into the building. It makes joints at these junctions watertight, while at the same time allowing the natural expansion and contraction of materials to continue.

Chimney flashing has three main components:

  • Base flashing. Installed at the front (lowest) part of the chimney, base flashing is a single sheet of chimney flashing. Base flashing extends over the front of the chimney and wraps slightly around the sides.
  • Step flashing. Installed along the sloped sides of the chimney, step flashing forms the first layer of protection. Step flashing typically extends under the shingles along the chimney.
  • Counter or Cap flashing. Installed in the mortar joints above the step flashing, cap flashing extends down over the step flashing to provide protection from falling rain.

The back (upper) side of the chimney is protected by flashing as well:

  • For chimneys that are wider than 24 inches or are constructed next to a steep roof, a saddle (sometimes called a “cricket”) is installed. A saddle is like a tiny dormer that is installed behind the chimney to direct rain and snow around the back of the chimney.
  • For narrower chimneys or chimneys constructed near a shallow roof, a continuous piece of chimney flashing called “backer flashing” is installed.