Why is my chimney leaking into the attic?
Short answer. Water running down the framing beside a chimney in the attic most often comes from failed step flashing or counterflashing where the roof meets the brick, a missing or failed cricket behind a wide chimney, a cracked crown on top, or water soaking through porous brick or mortar. When the stains appear, rain or no rain, helps tell a leak from condensation inside the flue.
Read the stains
- Wet only on the uphill side of the chimney: water is backing up behind it, which points to a missing or too small cricket or debris dams.
- Wet along the sides: step flashing or counterflashing failure.
- Wet framing all around, even far from the roof line: water entering from above, through the crown, cap or brick.
- Wet only during cold weather with no rain: condensation from flue gases, a venting issue for a chimney sweep or HVAC tech, not a roofer.
The usual culprits on the roof
- Step flashing: L-shaped pieces woven into each shingle course along the sides. Missing or reused pieces leak.
- Counterflashing: metal set into the mortar joints that laps over the step flashing. When it is caulked onto the face of the brick instead of cut into the joints, it fails as the caulk ages.
- Cricket: a small peaked diversion behind the chimney. The residential code calls for one when the chimney is wider than 30 inches along the ridge line.
- Crown and cap: a cracked mortar crown or missing cap lets water straight into the chimney structure.
Framed chimney chases
Many newer Georgia homes have chimneys framed and sided rather than brick. Leaks there often start at the metal chase cover on top, which rusts or ponds water.
A tube of sealant rarely fixes chimney leaks for long. See chimney leaks and crickets and roof flashing explained. Robust Roofing explains its approach in its guide to chimney flashing leaks.