Chimney cap installation in brief
A cap sits over the top of the flue and does three jobs: it sheds rain, blocks birds and animals, and keeps leaves and debris from dropping in. Installation means measuring the flue outlet, choosing a cap that fits the chimney and the appliance it vents, and fastening it so wind can't lift it off. A masonry chimney usually takes a cap that clamps or bolts to the flue tile or the top of the chimney. A factory-built chimney takes a cap made to fit its pipe. Materials, styles and each step of the process are covered on the chimney cap installation service page.
What affects chimney cap installation in Larkspur
- City of Larkspur Ordinance 1092, adopting the 2025 California Fire Code with local amendments, defines a spark arrestor and requires its net free area to be at least four times the chimney outlet's net free area. Under Larkspur Municipal Code Section 15.40.045, Central Marin Fire requires a resale report before the sale of any residential building or parcel in Larkspur's designated Wildland Urban Interface, effective January 7, 2026. Source: City of Larkspur - Staff Report Item 7.1A, Ordinance 1092 adopting the 2025 California Fire Code (Nov. 5, 2025); Central Marin Fire Department - Residential Resale Inspections.
Screen sizing under Larkspur's adopted fire code
City of Larkspur Ordinance 1092 adopts the 2025 California Fire Code with local amendments. It defines a spark arrestor and requires the arrestor's net free area to be at least four times the chimney outlet's net free area (source: City of Larkspur Staff Report Item 7.1A, Ordinance 1092 adopting the 2025 California Fire Code, Nov. 5, 2025).
Net free area is the open space air and smoke can actually pass through. For a screen, that means the openings only, not the wire. Most caps have a mesh screen around the sides, and that mesh does the spark-arresting work. The rule affects installation in a few practical ways:
- The flue outlet gets measured first. Its open area sets the minimum the screen has to provide.
- A cap that fits the flue tile can still fall short if the screen is short or the hood sits low. Screen height and perimeter both count toward the open area.
- An undersized screen also clogs faster with soot and creosote. That chokes the draft and can push smoke back into the room.
Already have a cap?
An existing cap doesn't meet the rule just because it is on the chimney. If you aren't sure how its screen compares with your flue, it can be measured during an estimate visit.
Selling a home in Larkspur's Wildland Urban Interface
Under Larkspur Municipal Code Section 15.40.045, Central Marin Fire requires a resale report before the sale of any residential building or parcel in Larkspur's designated Wildland Urban Interface. The requirement took effect January 7, 2026 (source: Central Marin Fire Department, Residential Resale Inspections).
If you're preparing to sell in that area, put the report on your timeline early and check with Central Marin Fire on what it involves. Separately from that report, a chimney inspection in Larkspur gives you a written look at the chimney's condition before listing, including whether the top of the flue is capped and screened.
When a new cap fits the job, and when something else comes first
A cap is the right job when the flue is open to the weather or the old cap is missing, rusted through or blown loose. It also fits when the screen falls short of the open-area rule above. If you're still weighing whether your chimney needs one at all, start with do you need a chimney cap.
Some situations call for different work before a cap goes on:
- Birds or animals already inside the flue need to be removed before it is closed off.
- Water stains on the ceiling or wall near the chimney often point to the flashing or masonry, not just an open flue.
- A cracked or crumbling top surface on a masonry chimney should be repaired so the cap has something solid to anchor to.
- Heavy soot or creosote buildup is best cleaned out first, so the new screen doesn't start out partly blocked.
Booking cap installation
Request an estimate and we'll measure the flue, check the top of the chimney and recommend a cap sized to it. Other work we handle in the area is listed on our Larkspur page.
Sources (1)
The sources of the Larkspur facts on this page.
- 1City of Larkspur - Staff Report Item 7.1A, Ordinance 1092 adopting the 2025 California Fire Code (Nov. 5, 2025); Central Marin Fire Department - Residential Resale Inspections
