View Full Version : Attic / crawl space ventilation in extreme fire hazard area

Alex K
04-03-2011, 10:49 PM

I have run into a bit of a dead end with respect to attic and crawl space ventilation. The main house area is 2200+ sq ft. The house is a heavily remodeled 1950s raised foundation light framing construction, hip roof. About 1/2 of the area has volume ceilings up to roof (or close) with R30 rigid insulation, the rest has normal ceilings with R19 in ceiling and uninsulated roof above. There are existing "normal" 14x5 eave vents that are about 50% short in terms of required area, there are 4 large dormer vents (no fans) and the crawl space has 11 14x5 vents, also undersized.

This is located in very high fire hazard area in Santa Barbara, CA foothills (the last fire in 2009 was <100' away). I am struggling to come up with a compliant, fire-safe, and effective method of ventilating attic and crawl spaces so that:

- fire embers cannot get sucked in (which rules out "normal" mesh-covered vents, also the city here does not like them)
- the attic can be effectively ventilated in the summer because the roof easily gets over 150F
- the crawl space underneath the house gets proper venting without having to punch holes in the foundation, which, although heavily reinforced in the recent years, is old and prone to cracking when engaged with big power tools.

I have considered the following idea, please tell me if I am missing something that makes this a BAD idea:

I can run a large size duct (12" for example) from the crawl space to the attic and equip it with a variable speed low-pressure fan (there is space for just such a thing in a decorative wall element in the living room). This way, the air will get sucked in from the existing above ground vents into the crawl space, then through the duct to the attic, and out the roof vents. The fan can be temperature controlled based on attic air temp. In summer, when it's extra hot it will run at high speed to get lots of cool air into the attic (and moisture would not be an issue), and in winter it can run very slowly to just get minimal ventilation.

I could also then get rid of all 14x6 eave vents that are not fire safe, even with fine mesh screens. With forced ventilation, the now-lacking crawl space ventilation will be remedied as well. Both ends of the duct shall have mesh screens to prevent rodents from getting through, etc. The crawl space vents are much less likely to suck in burning embers, it's not perfect, but better than under-eave vents.

If the above is a bad idea, what are my options? The plan is to soffit and stucco the eaves, so I can suggest a vented soffit all around. The fire issue with embers remains, unless the soffit has very small holes, in which case the attic will be under-ventilated and I will need an exhaust fan that will make fire problems more severe by sucking the air through the soffit, so I don't like this either.

I like to do things in a fully compliant way, and I have already talked to one of the inspectors here that I know... who couldn't offer much of an advice except the vented soffit and the heads-up about upcoming total prohibition of "normal" attic vents in high fire hazard zone in the city.

Thank you for reading,


chris mcintyre
04-04-2011, 07:05 PM
Icynene for the attic (no ventilation required) and a sealed/conditioned crawl space.

Scott Patterson
04-05-2011, 06:05 AM
I really do not have a clue about high fire areas, but.....................

You do not want to create negative air pressure in a crawlspace.

The cooling of an attic area is done by convection. Cool air enters low and the warmer air exits high.

As noted by Chris I would consider sealing the attic and using Icynene for the insulation in it.

What do other folks do to their homes in the area?

Gunnar Alquist
04-05-2011, 11:29 AM

There is a relatively new product for attic vents specifically designed to meet the new California WUI requirements. I really do not know much about them, other than they are available. I believe the vent screen is coated with something like fire caulk, that expands when heated. Therefore, they are essentially single-use. If the house survives a fire, the vent screens must be replaced.

Oh, yeah... I hear they aren't cheap.

Vulcan Vent (http://www.vulcanvents.com/index.htm)