lightning strike on roof of house

Chimney Flashing Leaks

Common in the Northwest are chimney flashing leaks. Beside vent pipes, chimney flashing is probably the number one cause of leaks we find during Seattle roof cleaning.

chimney flashing Flashing a brick chimney and a metal stack with a box covered in stucco or siding are two different things. The latter system is easy to deal with when flashing fails. Flashing are metal L shaped pieces that run up under the siding and then out under the roofing material above the underlayment. The strips are layered and over lapped so that water from above does not penetrate, in the same way the shingles are overlaid. Each strip of metal extends out over the underlying shingle so that water runs out over the shingles below. Properly installed, this flashing can last many, many years.

On brick chimneys, the flashing cannot be inserted underneath the exterior layer since the chimney does not have a surface layer. The chimney usually has a skirt that is attached in the mortar between the brick and the flashing is inserted up under the skirt.

The top edge of chimney has one long section of flashing that extends beyond the chimney sides, but wide chimneys also need a cricket. A cricket is a wedge shaped box that diverts water running down the chimney around it, so that it does not pool on the upper side of the chimney.

If the flashing corrodes or cracks, water may intrude into the roof and replacement may be necessary. Flashing can be caulked to seal it but this is a temporary measure that is bound to fail after a short period of time.

Pro Long recommends that the flashing be replaced if the roof is replaced. The one variation from this is the replacing of the skirt on a brick chimney. Since the skirt is secured into the mortar between the bricks, it is best to leave this alone unless deterioration is noticeable.

We at Pro Long replace chimney flashing when we find problems during Seattle roof cleaning or Bellevue roof cleaning jobs. We also replace the flashing when doing a Seattle or Bellevue roof replacement.