Download PDF version (508.2k) Log In or Register to view the full article as a PDF document.

Counterflashing

Image

Image

Image

Problem:

Counterflashing is pulling away from the chimney.

In the top photo, expansion and contraction have caused a failure of the caulk used to seal the surface-mounted counterflashing to the chimney. In the bottom photo, a too-shallow flange in the counterflashing has allowed water to get behind the flashing when the brick gets saturated in a heavy rain.

Solution:

Install the counterflashing between courses of brick as the chimney is being laid up.

The minimum width flange for counterflashing inserted into a brick chimney is 1-1/4 inches. For existing masonry, cut a 1-1/2-inch-deep kerf into a mortar joint with an abrasive blade. Run a bead of caulk along a 1/4-inch hem turned up on the back edge of the flange, then slide the flange into the kerf. The hem will compress slightly, holding the flange in place. Finally, caulk the top of the flange where it enters the kerf to keep excess water out.

Image

Image

Problem:

Failure of caulk between stucco and flashing.

Don't depend on caulk or roofing cement to keep water out of a crack anywhere on a roof, especially if the crack is between dissimilar materials, which expand and contract at different rates. Caulk has its uses, but it should not be relied upon as the primary barrier against water entry.

Solution:

Install overlapping flashings

that permit some movement. When stucco will be used above counterflashing, the counterflashing should be installed first, behind the stucco, and the felt underlayment should be lapped over the counterflashing.