Chimney guides

Spark Arrestor Requirements in California

The cheapest part on a California chimney is also the one most likely to be missing, corroded through, or blocked solid.

Fine stainless spark arrestor mesh fitted over a flue on a stucco chimney

Short answer

Across State Responsibility Areas a spark arrestor over the flue is a legal requirement, and the mesh opening is specified rather than left to preference. Many local fire codes require one regardless of SRA status. It is usually combined with the cap, so one component keeps rain and animals out and embers in. A blocked or corroded arrestor is its own hazard, because it stops the flue drawing.

What it is and where it is required

An arrestor is mesh fitted over the flue opening to stop burning fragments leaving the chimney. In fire country that is not theoretical — an ember carried on a wind is how a great many California fires start.

The requirement applies across State Responsibility Areas, which is a large share of the state, and the mesh aperture is set rather than being a matter of judgement. Many local fire authorities require one anywhere in their jurisdiction. If you are unsure whether you are in an SRA, your local fire authority will tell you.

Cap and arrestor are usually one part

A cap with correctly specified mesh sides does both jobs. A cap without mesh is not an arrestor, which is a distinction worth making when someone tells you the chimney already has a cap.

Why a blocked arrestor is worse than no arrestor

This is the part people do not expect. Mesh loads up with soot, particularly on a wood-burning appliance, and a blocked arrestor is a blocked flue.

A flue that will not draw pushes smoke back into the room, makes the appliance burn badly, and in the worst case spills combustion products into living space. So the arrestor is not a fit-and-forget item. It needs looking at annually, and on a regularly used wood appliance it needs clearing.

Mesh too fine is the same problem

An arrestor with an opening smaller than specified blocks faster and restricts draft even when clean. Correct is correct — finer is not safer.

Corrosion near the coast

Galvanized mesh does not survive marine air. From San Diego up through the Bay Area, stainless mesh and stainless fixings are the only sensible specification, and that includes the screws.

Checking what you have

A great many older California chimneys have no arrestor at all, or have one that corroded away years ago, or have one so blocked it might as well be a lid. None of that is visible from the ground.

The sensible time to check is with the annual inspection, because the arrestor is at the top of the chimney and that is where the inspection goes anyway. Clearing it as part of that visit costs almost nothing; as a separate call-out it costs a great deal more.

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Frequently asked questions

Is an arrestor legally required everywhere in California?

In State Responsibility Areas, yes, with a specified mesh aperture. Many local codes require one beyond those areas. Check with your local fire authority.

Will the mesh restrict my fireplace?

Correctly specified mesh does not. Mesh that is too fine, or mesh that has loaded with soot, does — and that is the more common complaint.

Can I fit one myself?

The part is available. Working at the top of a chimney is the risk, and getting the aperture and the fixing right matters when it is a code requirement.