A chimney chase is rotting when water has gotten past the chase cover or the siding and soaked the wood framing and sheathing inside. The early signs are visible from the yard: rust streaks running down the siding from the top of the chase, a chase cover that sags or holds a puddle, siding that has cupped, split, or turned dark near the top, and trim that feels soft when pressed. Inside, you may see water stains on the ceiling or wall next to the fireplace, or a musty smell from the firebox area after heavy rain.
A chase rebuild fixes the damage at its source. We remove the rotted framing, sheathing, and siding, rebuild the structure to the clearances the fireplace and vent need, wrap it, re-side it to match the house, and top it with a new cover and cap so water cannot get back in. Chase rebuilds start at $299, and smaller chase repairs cost less. Here is how to tell what you are dealing with and what the work looks like.
What a chimney chase is, and why it rots
If your house was built after about 1985, or it is a townhome, there is a good chance your "chimney" is not brick at all. It is a framed wood box, sided to match the house, with a factory-built fireplace and a metal flue pipe inside. That box is the chase. On top sits a flat or slightly sloped metal lid called the chase cover, with a hole for the flue pipe and a cap over the pipe.
Chases rot for one reason: water gets in and cannot get out. The usual entry points are these.
A rusted or badly made chase cover
Most original chase covers are galvanized steel. Over years of rain the coating wears through and the cover rusts, first at the flue collar and the corners, then in pinholes across the flat. A cover that was made flat instead of sloped, or without a drip edge, holds standing water and rusts faster. Once it leaks, water drops directly onto the top plate of the framing. In Seattle, where about 73 percent of the year's rain falls between October and March and November averages over six inches, a leaking cover can keep the top of the chase wet for months at a stretch.
Failed siding, trim, or caulk
The chase is an exterior wall that nobody looks at. Caulk at the corners and around the cover dries out, siding joints open up, and water gets behind the siding. Because the chase is hollow and unheated, it dries slowly, especially on the north side of a roof or under trees.
Bad flashing at the roof
Where the chase passes through or sits against the roof, step flashing and counter flashing keep water out. If it was installed wrong or has lifted, water runs down inside the chase from the roofline.
No cap or the wrong cap
A missing cap lets rain straight into the flue pipe and onto the fireplace. It also lets animals in. Our chimney cap page covers what belongs on top of a prefab flue.
Signs your chimney chase is rotting
From the ground
- Rust streaks. Orange or brown streaks running down the siding from under the chase cover. This is the single most reliable early sign that the cover has started to fail.
- A sagging or puddled cover. Look at the cover from across the yard. If the middle dips or you can see standing water after rain, it has been holding water and is either rusting or already leaking.
- Dark, cupped, or split siding at the top. Wood and composite siding that stays wet changes color and shape. Damage starts near the top and works down.
- Peeling paint. Paint lifts when moisture pushes out from behind it.
- Soft trim or corner boards. If the trim at the top corners gives under thumb pressure, the wood behind it is wet.
- Moss or algae on the chase. Growth on the siding means that surface stays damp, which is the condition rot needs.
From inside the house
- Stains on the ceiling or wall next to the fireplace. Water that gets into the chase runs down the framing and shows up at the nearest drywall.
- Water or rust in the firebox. Drips through the flue collar land on top of the fireplace unit and can run into the firebox.
- A musty smell near the fireplace after rain. Wet framing and insulation inside a closed chase smell exactly like a damp basement.
- Rust on the fireplace unit. Rust at the top of the firebox or on the flue pipe where it meets the unit means water has been dripping on it.
What we check that you cannot see
During an inspection we get on the roof, lift the cover if it is loose, and probe the top plate and sheathing. We look at the flue pipe for rust and at the firebox for water marks. We check the clearances between the flue pipe and the framing, because a rotted chase sometimes gets a quick siding patch that leaves framing too close to the pipe. That is a fire issue, not just a water issue. You do not need to go on the roof; we do all of it.
Chase repair versus chase rebuild
Not every wet chase needs a rebuild. The line between a chase repair and a chase rebuild is how far the rot has traveled.
Repair
If the cover failed recently and the rot is limited to the top plate, the top few inches of sheathing, and some trim, we replace those pieces, reseal, and install a new cover and cap. This is common on chases where the homeowner caught the rust streaks early.
Rebuild
If the rot has run down the studs, the sheathing is soft across a large area, the siding has to come off to get to it, or the framing has pulled away from the house, the chase gets rebuilt. This is what we usually find when a cover has been leaking through several Seattle winters.
What a chase rebuild involves
- Demolition. We remove the old cover, cap, siding, trim, sheathing, and every piece of rotted framing, down to sound wood. Everything is hauled away.
- Framing. New framing is built to the clearances the fireplace unit and flue pipe call for, tied into the existing structure.
- Sheathing and wrap. New sheathing goes on, followed by housewrap so water that gets behind the siding drains out instead of soaking in.
- Flashing. Step and counter flashing at the roofline, done right this time.
- Siding and trim. Matched to the house as closely as the material allows, with joints and corners sealed.
- New chase cover. A cover fabricated to fit, with a cross-break or slope so water sheds, a drip edge that carries water past the siding, and a raised collar at the flue. We use materials that do not rust through the way galvanized steel does. Chase cover replacement on its own starts at $299; in a rebuild it is part of the job.
- Cap. A cap sized for the flue pipe to keep rain, animals, and debris out.
- Final check. We photograph the finished work, confirm clearances, and walk you through it.
Chase rebuilds start at $299. The final number depends on how much framing is rotted, the height of the chase, and the siding material. We give you a written quote before any work starts, and if you are not happy with the result, we are not done: we come back and make it right at no charge.
Why Seattle chases rot faster than the cover's warranty card suggests
Chases are most common in the parts of the region built after the mid-1980s: Renton's Benson and Fairwood plats, Bothell, Redmond, Auburn's Lakeland Hills, south Everett, and Gig Harbor. Those neighborhoods are now old enough that original galvanized covers are at the end of their life all at once. Add a climate where the chase top stays wet from October through March and moss grows on any shaded surface, and rot is the expected outcome, not a surprise.
The good news is that a chase is cheaper and faster to rebuild than a brick chimney, and a new cover and cap on a sound chase should take it through many more wet seasons.
What to do next
- Walk to the far side of the yard and look at the chase: rust streaks, a sagging cover, dark or cupped siding near the top. Do not climb on the roof.
- Check the ceiling and wall beside the fireplace for stains, and look in the firebox for rust or water marks.
- If you see any of those, stop using the fireplace until someone has confirmed the flue pipe and clearances are sound.
- Call 206-453-2045 or request a free quote. We inspect the cover, framing, flashing, and fireplace unit, show you photos, and quote the repair or rebuild in writing. Same-day service is often available in Seattle, Renton, Tacoma, Everett, and the road-accessible Puget Sound, including Gig Harbor via the Tacoma Narrows Bridge.
- Have a quote already? Ask for our free second opinion. We price match and take 10 to 25 percent off.
Seattle Chimney Repair Services is certified and insured, uses safe and green materials, and guarantees the work: if you are not happy, we are not done.
Questions homeowners ask
What is a chimney chase?
A chase is a framed wood box, sided to match the house, that encloses a factory-built fireplace and its metal flue pipe. It is topped by a metal chase cover and a cap. Most homes in the Puget Sound built after the mid-1980s, and most townhomes, have a chase rather than a brick chimney.
What are the first signs a chase is rotting?
Rust streaks on the siding below the chase cover, a cover that sags or holds water, and siding or trim near the top that is dark, cupped, or soft. Inside, look for stains on the ceiling beside the fireplace and rust or water in the firebox.
Can a rotting chase be repaired without a full rebuild?
Yes, if the rot is limited to the top plate, the top few inches of sheathing, and some trim. We replace those pieces and install a new cover and cap. Once rot has run down the studs or across the sheathing, a rebuild is the right fix. Chase rebuilds start at $299.
Is a rotted chase a fire hazard?
It can be. Rotted framing can shift, and patched chases sometimes leave framing too close to the flue pipe. We check clearances on every chase inspection. If you see rot or water in the firebox, stop using the fireplace until it has been inspected.
How long does a chase rebuild take?
It depends on the amount of rot, the height of the chase, and the siding. We give you a written quote and a time estimate after the inspection, and same-day service is often available for inspections and smaller repairs.
Related