What causes a chimney leak?
A chimney leak is water entering the house along or through a chimney. There are three ways in. At the roof line, water slips past the flashing where brick or siding meets the roofing. Through the masonry, rain soaks into porous brick and cracked mortar and travels down inside the chimney. From the top, it falls straight down the flue past a missing cap or a cracked crown.
Novato's housing stock makes chimneys a common call. Many homes built during the city's 1960s and 1970s growth have wood-burning fireplaces with brick chimneys, and plenty of older homes in Petaluma, San Rafael and San Anselmo have chimneys that are a century old. Those chimneys have seen decades of dry summers, wet winters and the occasional shake, and their flashing has usually been patched more than once.
Where the water shows up is a clue. Stains on the ceiling or wall beside the chimney point to the roof line. Water inside the firebox, or a damp smell from the fireplace, points to the top or the masonry.
How chimney leaks are fixed
- Step and counterflashing. The most lasting repair. Step flashing pieces are woven into each course of roofing along the sides, and counterflashing is cut into the mortar joints and folded down over them, so water never meets an exposed seam.
- Cricket or saddle. Wide chimneys get a small peaked roof on the uphill side to split water and debris around them.
- Crown repair. The cement cap at the top of the masonry is patched or rebuilt so it sheds water past the edge of the brick.
- Chimney cap. A metal cap over the flue keeps rain, leaves and animals out.
- Masonry work. Repointing cracked mortar joints and, where suitable, applying a breathable water repellent to the brick.
Roofers handle the flashing and cricket work. Crown, cap and masonry repairs may be done by the same contractor or by a chimney or masonry specialist they bring in, so ask who will cover each part.
Eight signs of a chimney leak
- A stain on the ceiling or wall right beside the chimney
- Water or rust streaks inside the firebox or on the damper
- A musty or damp smell from the fireplace after rain
- White powdery deposits on the brick, inside or out
- Cracked or crumbling mortar between bricks
- A cracked or broken crown at the top of the chimney
- Flashing that is lifted, rusted or covered in old tar
- Wood trim or siding around the chimney that is swollen or soft
Why Marin chimneys leak
Patched flashing is the most common cause. Over several reroofs, chimney flashing is often left in place and covered with roofing cement instead of being replaced. Each layer of tar dries and cracks in the summer heat, and the first storms of winter run straight into the gaps.
The masonry itself ages too. Brick and mortar soak up water and dry out again every season. Mortar joints soften, the crown at the top cracks from sun and settling, and on older homes the brick may have shifted from past earthquakes. Water that gets into the masonry follows it down and appears inside.
Debris and trees play a role in Marin as well. Leaves and needles collect behind wide chimneys with no cricket, holding water against the uphill flashing. Branches rubbing against the chimney chip mortar and loosen caps, and missing caps let leaves and rain fall straight into the flue.
Safe checks from the ground and inside
- Look inside the firebox with a flashlight after rain for water, rust or fresh stains.
- Check the wall and ceiling next to the chimney for stains or bubbling paint.
- Use binoculars to look at the cap, crown and flashing from the yard.
- Note whether the leak happens in all rain or only in wind from one direction.
- Find any chimney or roof records showing when the flashing was last replaced.
Close the fireplace damper during the rainy season if you are not using it. It will not stop a leak, but it keeps falling water and debris from reaching the room while you wait for a repair.
Brick, block and framed chimneys
Not every chimney here is brick. Many Novato homes from the building boom have brick or concrete block chimneys for wood fireplaces, while others have a framed chase, a wood box covered in siding or stucco that wraps a metal flue. Framed chases leak in their own way: at the metal chase cover on top, which rusts and pools water, and at the siding where it meets the roof.
Older homes in Petaluma, San Rafael's Gerstle Park and San Anselmo may have tall, slender brick chimneys with little or no reinforcement. Those are worth checking closely after any earthquake or windstorm, because a crack near the roof line both lets in water and weakens the stack. Telling the roofer which kind you have, and whether it vents a fireplace, insert or furnace, helps them bring the right materials.
The roofer's chimney visit
- Inside check. The roofer looks at the stains, the firebox and the attic around the chimney chase.
- Roof line. On the roof, they check step flashing, counterflashing and the uphill side for debris or a missing cricket.
- Top of the chimney. They inspect the crown, the cap and the mortar joints near the top.
- Water test. If needed, they wet the roof line, then the masonry, then the top, in that order, to find the entry.
- Scope. They explain what is roofing work and what is masonry, with photos.
- Repair. New flashing, a cricket, a cap or crown repair is completed, with masonry handed off if needed.
Factors that shape a chimney repair
| Factor | Effect |
|---|---|
| Chimney width | Wider chimneys usually need a cricket on the uphill side. |
| Roof covering | Shingle, tile and shake roofs need different flashing methods. |
| Masonry condition | Cracked crowns and soft mortar bring in a mason. |
| Chimney height | Tall chimneys and steep roofs need more staging. |
| Interior damage | Long-running leaks add drywall, trim or framing repair. |
When a chimney leak is urgent
Call promptly if water is running down the wall or into the firebox in every storm, if bricks or pieces of crown have fallen, or if the chimney looks like it is leaning or separating from the house. A damaged chimney can shed masonry onto the roof or the yard.
Keep people and pets away from the base of a chimney with loose bricks, and do not climb up to inspect it yourself. If water has reached the flue or firebox, have the chimney checked before lighting another fire.
Chimney leak questions
Is a chimney leak a roofing job or a masonry job?
Often both. Flashing where the chimney meets the roof is roofing work; cracked crowns, mortar joints and brick are masonry. Many roofers handle flashing and crickets and bring in or recommend a mason for the rest.
Why does water show up inside my firebox?
Rain is entering from the top, usually through a missing cap, a cracked crown or a gap at the flue. Water that comes in at the roof line tends to show on the wall or ceiling beside the chimney instead.
What is a chimney cricket?
A small peaked structure on the uphill side of a wide chimney that splits water around it. Without one, water and debris pile up behind the chimney and work under the flashing.
Can sealant fix chimney flashing?
Sealant can hold briefly, but it cracks as brick and roof move with heat and cold. Lasting repairs use step flashing woven into the roofing and counterflashing set into the mortar joints.
Should I stop using the fireplace if the chimney leaks?
If water is getting into the flue or firebox, have the chimney checked before the next fire. Water can damage flue liners and mortar, which affects safe venting.
My chimney was damaged in an earthquake years ago. Could that cause leaks?
Cracked mortar joints and a shifted crown from past shaking can let water in. A roofer or mason can look for cracks and separation where the chimney meets the roof.
Related pages
Leaves stacking up behind a chimney are part of the wider debris problem on moss and debris. Petaluma's older west-side homes have some of the oldest chimneys on this line, covered on the Petaluma page.
For water that came in after a windstorm, see storm and tree damage, or start from roof leak repair in Novato to match your stain with the leak checker.