How Vented Attics Worsened the LA Fires

Youtube ^ | January 25, 2025 | ASIRI Designs

[House Atreides]

Vented attics are a major contributing factor when it comes to the spread of wildfires, as embers that are in the air are drawn into the attic space, resulting in an attic fire. Many homes and buildings in California feature vented attics and this significantly exacerbated the intensity and spread of the 2025 wildfires. This isn't just a California problem, this is anywhere that is prone to wildfires. Unvented conditioned attic assemblies are significantly safer in wildfire zones, as they do not allow outside air or embers to enter the roof assembly. In this video, we discuss why vented attics increase your risk of a fire and how switching to an unvented conditioned attic assembly with a vapor diffusion port is cost effective and safer.

[ProtectOurFreedom]

Thanks. This has been known for decades, but it never hurts to instruct and inform people again and again (especially people under 40 years of age who were only 10 years old when this article was published).

Fine Homebuilding Magazine, Issue 96, July 1995
By John Underwood

Fire-Resistant Details
Studying the houses that survived the 1993 Laguna Beach fire storm yields lessons in building to withstand the heat.

Survival of the fittest. Why did some houses-such as that of To Bui and Doris Bender-survive the Laguna Beach fire storm of 1993, while those around them burned? The answer is found in careful construction details that reduced the amount of exposed combustible material and insulated the insides of the houses long enough for the fire to pass by.

“Keeping the envelope sealed can buy precious time.”

• No exposed wood.
• Thick stucco on every surface.
• No attic vents.
• Thick, heavily insulated walls.
• 5/8" Type-X fire-rated sheetrock on exterior walls between plywood shear wall and the stucco.
• No eaves, eliminate the overhang, plug all holes with cement.
• One-hour-rated exterior doors AND jambs.
• Class-A cement-tile roof.
• Wooden deck surfaces troweled over with several layers of fire-resistant coating.
• Undersides of all decking are stuccoed over with a 1 inch layer of cement.
• On downhill slopes, 40 ft. or more of "ice plant" (Californians will know what this is)

[Brian Griffin]

One should seal the vents upon an evacuation order and unseal them upon return.

[crz]

Wont be talking about this in a day or so.
There is flood warnings around there now.

They’ll be talking about flood control.

Lol.

[Teflonic]

[Pollard]

Unvented conditioned attic assemblies

Cooling a sealed attic with the summer sun beating down on it? That would triple your summer electric bill. The reason for incoming soffit vents and outgoing gable vents is to keep the attic from getting way hotter than the outdoor temp and also prevent mold from humidity.

I wonder if operable vents along with grid fed smoke detectors and relays to close the vents would work? Just something else to inspect and maintain of course.

Soffit/gable vents with metal screens would do a lot. Soffit vents are slotted vinyl and may have fiberglass screens.

[Carry_Okie]

Better screens on the vents are an easy fix.

[txeagle]

The International Residential Code specifies that conventional attics be ventilated at a rate of 1 square foot of vent opening for each 150-300 sqft of attic area depending on the region in which the house is built. Openings are roughly equally divided between eaves and ridges/upper roof areas to attain convective air flow to draft hot air out of the attic.

Closed attics are generally accomplished by spraying foam insulation in rafter bays and deleting soffit and ridge openings, deleting insulation in ceiling joist bays as well as providing a small amount of conditioned air flow. In essence, the attic becomes part of a home’s conditioned volume.

Both have their plusses and minuses. An un- or under-vented and/or improperly insulated attic in my part of Texas can easily heat up in excess of 160 degrees on relatively normal summer days. In winter, it retains moisture that can compress insulation and promote mold growth.

Closed attics are technically more efficient but foam applied to the underside of a roof deck can hide leaks until they reach a point of catastrophic failure. Insurance companies are beginning to deny coverage for these types of installations where I live because of that.

[Carry_Okie]

Works great for fire protection.

Unless it's engineered for the extra weight, it's a lousy idea against an earthquake.

[cableguymn]

I know it keeps the damp out of the air space..

short of that, I don’t know.

[CivilWarBrewing]

Attic temps are a HUGE reason for venting, especially in hot areas. ALSO, some homes have their A/C AND FURNACE WITHIN THE ATTIC. Ventilation is a MUST!

The question I have is, how about sealing the attic vents on the sides of the home and achieve ventilation with TURBINES instead? Would turbines help reduce fire danger from embers?

[ProtectOurFreedom]

The only big increase in weight is the tile roof. As you point out, the roof, wall and foundation structures must be engineered for the additional roof mass. But it is doable.

Wildfires are more common than earthquakes...and generally a LOT more destructive.

In any event, the extra cost for fire and earthquake safety is minimal and all EQ design details are already in the code.

[Jeff Chandler]

Ventilation is vital . . . Not so much in the desert Southwest

Seriously?

[Cincinnatus.45-70]

Composition shingles? I saw an article last week where a burnt out LA homeowner was saying he had wood shingles. Does anyone here know if wood shingles were allowed in LA?

[Presbyterian Reporter]

“””Would turbines help reduce fire danger from embers?”””

---

Maybe.

But all of these potential fixes ignore the reality.

The Los Angeles area has had brush and tree fires for decades. And still they continue to build houses close to the brush and trees.

So until Los Angeles builds massive fire breaks on the ridges surrounding these houses as well as removes trees and brush several hundred feet from the houses, these fires will continue to wreak havoc.

[packagingguy]

I had this problem with my house. The previous owner was cheap.

He turned an open attic into a closed one and had AC unit that was 1 ton too small.

It ran continuously all summer.

I removed the plugs over the vents and bought a properly sized AC unit. My power bill went down.

[gundog]

Some people just think shake roofing is so cool, aesthetically. Not worth it, in LA. If they aren’t outlawed, insurance will likely be expensive or unavailable.

[cyclotic]

There some science to ventilation. It needs to allow the air to follow a path. Just venting isn’t helpful as the air just turbulates in the attic. Having a specific path with entry vents like soffit vents and roof exit vents works great to keep the attic space properly vented.

My home uses soffit vents and turbine vents on the roof. They are ugly but are by far the most efficient.

[gundog]

Thinking on it further, there are probably a lot of vaulted ceilings in the LA area. Shakes can be useful over those areas, but yeah....fire. 🔥

[Cold Heart]

Depending on the climate, an unvented attic can rot. An unvented attic in warm clmate can get really hot.

My vents have screens that won’t allow small particles to enter.

Maybe double screening in some areas would work. They definetly need some anti-fire construction like Chicago did after their great fire.

It is code in my state which follows a national code.

[catnipman]

“Is there some code requirements that require venting? Or some advantage, maybe in cooling?”

the purpose of attic venting is to keep warm moisture from the interior of your house from building up in the attic and then condensing on the underside of your cold roof during the winter, esp. in humid climates, and thereby rotting the roof sheeting ...

many decades ago, a friend’s father in my neighborhood thought he was being energy-smart by having his gable vents sealed off ... a few years later, he found out all of his roof sheeting had rotted and had to be replaced ...