Chimney Caps with 3/4 Inch Mesh or
Chimney Caps with 5/8 Inch Mesh: 
What's the Difference?
© 2006 PennVentures LLC

Is there a difference between chimney caps with ³/4" mesh and chimney caps with ⁵/8" mesh? Is it a difference I need to know about before I select a chimney cap?

Yes, there is a difference between ³/4" and ⁵/8" mesh chimney caps, and, depending on where you live or other special circumstances, it might be a difference you need to take into account when buying your chimney cap.

The "mesh" is the screen part of the chimney cap. It is the section below the "lid" or roof that lets the gases out of your chimney but keeps leaves and birds, insects, and other animals from getting into your home. The two mesh sizes for chimney caps are ³/4" or ⁵/8", with the ³/4" mesh having slightly larger holes in the screen than the ⁵/8" mesh has.

The vast majority of American chimney caps have ³/4" mesh. But many localities — primarily California, but also some in other areas around the country — have building codes that call for chimney caps with "¹/2 inch spark arrestors." Some localities call for such chimney caps in wooded areas or within 200 feet of wooded areas. The purpose of chimney caps with "¹/2 inch spark arrestors" is to prevent sparks and burning detritus that are a half inch or larger from escaping from chimney caps and starting wild fires.

So what are chimney caps with "¹/2 inch spark arrestors"?  According to the National Fire Protection Association, chimney caps with ⁵/8" mesh will not allow a half-inch sphere through them. Chimney caps with ⁵/8" mesh, therefore, are considered the industry standard for all localities that require chimney caps with "¹/2 inch spark arrestors."

Since so many of the chimney caps with the smaller, ⁵/8" mesh are used in California, chimney caps with the ⁵/8" mesh are also often called California-style chimney caps.

How will I know if I need a California style, ⁵/8" mesh chimney cap? If you are buying a home, ask the realtor. If you already own the home, you can call the local government department that deals with building codes such as the department that issues building permits. You local chimney sweep will also know.

Would I ever want California style, ⁵/8" mesh chimney caps if my local building codes don't require them?  Yes, some people select chimney caps with ⁵/8" mesh even though they are not required by their locality. People who have wooden roofs on their home or outbuildings, those with woods near their homes, and others who live in dry areas that are susceptible to wild fires have chosen to buy chimney caps with ⁵/8" mesh to reduce the likelihood that a spark escaping from their chimney cap could start an outside fire.

There's one other reason people might select chimney caps with ⁵/8" mesh. If you have an oval flue and want a chimney cap that mounts to the flue instead of to the crown of your chimney, consider a ⁵/8" mesh chimney cap. It is not unusual for homes in California, Arizona, Nevada, and Oregon to have oval flues, so some chimney cap manufacturers make ⁵/8" mesh chimney caps with a special base that can fit either a rectangular flue or an oval flue.

Chimney caps with ⁵/8" mesh are manufactured to meet local building codes designed to reduce wild fires. But you might have a special circumstance, such as a roof or exterior environment susceptible to fire, which might lead you to select such a chimney cap even if your local codes do not require ⁵/8" mesh chimney caps.