by Kenton Shepard and Nick Gromicko
Counter-flashing is designed to prevent moisture from entering behind the vertical flange of headwall or sidewall flashing.
Sometimes, the exterior wall-covering material serves as the counter-flashing, and sometimes a separate counter-flashing might be installed. Counter-flashing is especially important where walls are brick.
Counter-Flashing at Brick Headwalls and Sidewalls
Installing headwall and sidewall flashing correctly becomes more time-consuming when the exterior wall covering is brick. “Time-consuming” means “more expensive,” which is why most of the counter-flashing you’ll see at brick and stone walls will be incorrectly installed and will rely on a sealant alone to prevent moisture intrusion. Sealant eventually dries, shrinks and cracks, leaving an avenue for moisture intrusion.
Properly installed, counter-flashing sections are inserted into the mortar joints, and then the joint is sealed with an appropriate sealant.
Counter-flashing can also be inserted into a groove cut into the brick, and then sealed. Sealant here has been poorly applied and has left gaps that moisture can enter. This condition has the potential to cause freeze damage.
Here’s an example of counter-flashing installed in mortar joints which were never properly filled.
And here you see a similar situation where someone tried to make it look as though they had installed counter-flashing correctly. This flashing isn’t sealed or even fastened to the brick, leaving an avenue for moisture to enter behind it and leak into the roof structure.
Here’s an example of counter-flashing that sort of does and sort of doesn’t protect the flashing.
And here’s an example where it’s just missing!
Counter-Flashing at Stone Headwalls and Sidewalls
Here are examples of stone headwall and sidewall conditions flashed correctly, with counter-flashing extending up behind the stone, and a space left between the bottom of the stone and the roof surface.
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