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Chimney spark arrestors
A spark arrestor is 3/8- to 1/2-inch noncombustible metal mesh on a chimney or stovepipe outlet. CAL FIRE’s low-cost list names that range. It is not attic-vent mesh. IBHS wants branches 10 feet from the outlet. Oregon R327 .3.2 does not name fireplaces. The chase is still a wall.
You are on the roof with a tape on the cap, or you are looking at 1/8 inch hardware cloth someone stapled over the flue because the attic rule said “all vents.” Those are two different holes. One is a chimney. The other is building ventilation.
No g3-passed exhibit matches this object. DET-009 is still a brief. The scene is the cap. Do not use a house-level hub graphic as a flue detail.
Why it matters
Embers leave a burning fireplace and land on the Class A roof you just bought. They also enter a chase that was treated as trim. People mesh the flue like an attic vent and choke the draft, or they skip the cap because R327.3.2 never said “chimney.” The hardening ladder already lists the spark arrestor as a close-the-holes item. This page is the hole.
How the documents split
| Object | What it is | What it is not |
|---|---|---|
| Spark arrestor (CAL FIRE list) | 3/8- to 1/2-inch corrosion-resistant metal screen on chimney and stovepipe outlets | 1/16–1/8 inch attic mesh |
| Attic, gable, crawlspace vent | R327.3.2 mesh or a listed ASTM E2886 vent | A flue |
| IBHS 10-foot clearance | Branches away from chimney and stovepipe outlets | A mesh size |
| Fireplace opening (seminar) | Outside R327.3.2 | A skip of the wall covering |
| Chimney chase | A wall and a roof-to-wall line | An eave exception |
The paths
1. Screen the outlet. CAL FIRE item 4. Noncombustible, corrosion-resistant metal. Openings 3/8 to 1/2 inch. That is coarser than the attic band on purpose. Do not use the dryer rule either. See dryer vents versus mesh.
2. Keep fuel off the cap. IBHS 5–30 foot zone. Branches a minimum of 10 feet from chimney and stovepipe outlets. FEMA P-737 (2008) Fact Sheet 4 says keep branches from overhanging the roof and chimney. That is vegetation, not a listing.
3. Do not file it under R327.3.2. Where R327 is adopted, that subsection is enclosed attic, soffit, rafter, and underfloor ventilation openings. Presenters at the 25 June 2026 seminar put fireplaces with bath fans and fresh-air intakes, outside that subsection. Confirm with the building official. A spark arrestor can still be required by the mechanical or residential chimney chapter, a carrier checklist, or CAL FIRE’s list. Ask which document.
4. Treat the chase as a wall. R327.3.3 is the wall menu. Covering still runs. Flashing at the roof is roof-to-wall. FEMA P-737 2008 has no chase-framing fact sheet. This page does not draw one. Do not call the chase a gable-end overhang exception.
5. Carrier extras. Some agencies add a spark arrestor to an IBHS packet. IBHS does not replace adopted code. The 2025 standard’s chimney sentence is the 10-foot clearance.
What people mix up
- Putting 1/8 inch attic mesh on the flue.
- Skipping the cap because R327.3.2 is silent.
- Treating IBHS 10 feet as a mesh size.
- Treating a roadside Firewise plaque as a spark arrestor.
- Inventing a chase-framing recipe from a catalog line. P-737 2008 does not have that sheet.
How to check
- Open the cap. Measure the openings. CAL FIRE’s range is 3/8 to 1/2 inch.
- Look up. Branches inside 10 feet of the outlet fail the IBHS clearance even if the mesh is right.
- Walk the chase as a wall. Covering, cracks, roof flashing, needle traps.
- If someone specified 1/16 inch on the flue, stop. That is the attic rule on the wrong hole.
- Ask the official whether a chimney chapter, not R327.3.2, is the spark-arrestor trigger.
Limits
This page does not size a flue. It does not replace a chimney sweep. It does not reprint California Residential Code Chapter 10. That chapter did not open as a full public page in this session. FireApproved is not CAL FIRE, not IBHS, and not the AHJ. Confirm the document that actually binds the job.
Related records
Questions
Can I put 1/8 inch attic mesh on the chimney?
Not as the CAL FIRE spark-arrestor item. That list wants 3/8- to 1/2-inch openings on chimney and stovepipe outlets. Attic, gable, and crawlspace mesh is 1/16 to 1/8 inch. Finer mesh on a flue is a draft and creosote problem. They are different holes.
Does Oregon R327 require a spark arrestor?
R327.3.2 names ventilation openings for enclosed attics, soffits, rafter spaces, and underfloor spaces. It does not name chimneys or fireplaces. Presenters at the 25 June 2026 Central Oregon seminar said mechanical openings such as fireplaces sit outside R327.3.2. CAL FIRE’s list is retrofit guidance, not that section.
Does IBHS require the spark arrestor?
The 2025 Wildfire Prepared Home technical standard requires branches a minimum of 10 feet from chimney and stovepipe outlets. It does not name a spark-arrestor mesh. Some carriers add a spark arrestor to an IBHS field checklist. Treat that extra as carrier practice unless the current standard lists it.
Is the chimney chase an eave?
No. The outlet is the cap. The chase is a wall and a roof-to-wall line. Covering, flashing, and debris still follow the wall and roof rules. FEMA P-737 2008 has no chimney-chase framing sheet. This page does not invent one.