A cap only works if it matches the flue under it, the crown around it and the appliance below. Each flue is measured before anything is ordered.
The scope and price come to you in writing, and the cap goes on only once you have said yes. Photos of the chimney top before and after the work go to you as well.
What a cap is for
Rain down the flue
An open flue funnels rain onto the damper, smoke chamber and firebox. A rusted damper or a wet firebox after storms is a common clue.
Nesting birds and animals
A sheltered flue invites nesting. The material blocks the flue and can burn, and animals that climb in often cannot climb out.
Leaves and debris
Needles and leaves from nearby trees fall straight into an uncapped flue. They can build up on the smoke shelf or damper.
Embers
The mesh sides work as a spark screen, catching larger embers before they reach the roof. That lowers the risk; it does not remove it.
Rusted or loose caps
A cap that has rusted through or lifted in a windstorm lets in what it was meant to stop. Rust streaks below the flue often mean a steel cap is failing.
The parts named on this page, from the cap and crown at the top to the flashing where the chimney meets the roof.
What cap installation includes
Measuring each flue
Flue tiles vary, and two on one chimney may differ. Each outlet and the crown are measured so the cap fits what is there, not the nearest stock size.
Single-flue or multi-flue
A single-flue cap clamps to one tile. A multi-flue cap covers two or more flues under one lid and anchors to the crown or the outside of the chimney; the number of flues, their height and the crown’s condition decide which fits.
Mesh matched to the flue
Smaller openings stop more animals and embers but clog with soot sooner, and a clogged screen can push smoke back into the room. The mesh is chosen with the appliance in mind.
Metal for a wet roof
Stainless steel and copper generally handle constant moisture better than galvanized steel, which tends to rust where its coating is cut or drilled. The metal is chosen for the wet Puget Sound climate and agreed in the scope.
Attached to come off again
The cap is held with clamps, bolts or anchors rather than sealant alone. It is set up to come off cleanly for sweeping and inspection.
A clear flue first
A cap never goes over a nest or a blockage. If something is inside, it is cleared first, often with a chimney sweeping visit.
A note on the rest of the top
Anything else seen up there is noted plainly as urgent, able to wait, or not needed.
When to inspect before capping
If the crown and flue look sound and you just want rain and animals kept out, a cap can be scoped on its own. Water indoors, a damp sooty smell after rain or a smoky fireplace call for finding the cause first.
A cap cannot make a damaged flue liner usable either. If the flue is in question, start with a chimney inspection.
A cap is not a crown
The crown is the sloped concrete or stone slab over the masonry, with the flue passing through it; the cap is the metal piece mounted above that opening. Washington’s residential code muddies this by calling the slab a “cap” and requiring it to slope, carry a drip edge and have a caulked separation around the flue liners.
A cap keeps rain out of the flue, while the crown sheds it off the chimney and should overhang the brick so runoff drips clear. A small cap over a crown with no overhang can simply move water onto it, so a cracked or flush crown needs crown repair.
Water entering at the roofline or through the brick is not a cap problem. It is covered by leak and flashing repair.
What affects the cost of a cap
Caps vary because chimneys do. These are the main variables.
- Number and size of flues
- One standard flue takes a stock cap; several flues or odd sizes often need a larger or custom one.
- The metal
- Galvanized, stainless and copper differ in cost and in how they handle months of rain.
- Access
- Roof pitch, height and roofing material add setup before the cap is touched.
- Removing the old cap
- A rusted, seized or mortared-on cap takes extra work to remove cleanly.
- Crown and tile condition
- A cracked crown or chipped tile may need attention before a cap can be anchored, or change which type will work.
You get a written scope and price before any repair work begins.
Caps and the Puget Sound wet season
The Western Regional Climate Center notes that western Washington often records precipitation on 20 to 25 days or more in each of December and January, with the wet-season wind mostly from the south or southwest. A cap anywhere from Arlington to Olympia and east to Snoqualmie spends those months damp, often with wind behind the rain, and the foothill and valley towns tend to be wetter than the lowlands. That is why metal that resists rust, mesh that stays open and a secure attachment matter as much as the style of cap.
Questions about chimney cap installation
Does my chimney need a cap?
Most open flues benefit from one, since rain, leaves and animals otherwise have a direct way in. The part the residential code requires on top of a masonry chimney is the crown, which is a separate piece.
Will a cap stop my chimney leaking?
Only if water is coming down the flue. Water also gets in through crowns, flashing and brick, which a cap does not touch, so have a leak traced before counting on one.
Can I cap a fireplace I never use?
Yes, but ventilated rather than airtight. For a chimney that is out of use yet still takes in rain, moisture-control guidance from the National Park Service points to a ventilated cap instead of sealing the flue shut. Mention the unused flue when you ask for an estimate.
My fireplace smokes on windy days. Will a cap help?
It may, since a lid breaks up wind blowing down the flue and some caps are designed for downdrafts. If it also smokes in still air, the cause is probably elsewhere, such as flue sizing or a blockage.
Sources for the facts on this page (5)
- Chapter 10 Chimneys and Fireplaces - Washington State Residential Code 2021 — UpCodes (reproducing the Washington State Residential Code 2021, based on IRC 2021). Accessed 2026-08-27.
- Four Low-Cost Recommendations to Prevent Major Water Damage — Chimney Safety Institute of America (CSIA), dated June 11, 2010. Accessed 2026-08-27.
- Water, not fire, causes most chimney damage — Chimney Safety Institute of America (CSIA) press release, hosted on the NCSG association platform. Accessed 2026-08-27.
- Preservation Briefs 39: Holding the Line - Controlling Unwanted Moisture in Historic Buildings — U.S. National Park Service, Heritage Preservation Services (Sharon C. Park, AIA). Accessed 2026-08-27.
- Climate of Washington (state climate narrative) — Western Regional Climate Center, Desert Research Institute. Accessed 2026-08-27.