Los Angeles County, California
Roof and Attic Ventilation in Los Angeles
Vents get cut in while the covering is off, so a re-roof is the moment attic ventilation gets sized properly. Here is what the code asks for, how net free area is worked out, and why most attics fall short at the eave.
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Roof and attic ventilation is intake vents low on the roof and exhaust vents high on it, cut and flashed into the roof plane. It runs on warm air rising, with no motor. The moment to fix it is the re-roof.
California Residential Code Section R806.2 sets how much venting an attic has to have, and the plan checker looks for it on the re-roof permit. In the City of Los Angeles that is LADBS, in unincorporated county it is County Building and Safety, and contract cities run their own counters.
- What it isPassive intake low on the roof and exhaust high on it, cut into the roof plane
- The codeCRC R806.2: 1/150 of the vented area, or 1/300 where it is split high and low
- When to do itWith the re-roof, because the vents go through the covering
- In a fire zoneVents listed by the State Fire Marshal, or tested to ASTM E2886
How a vented attic works
Hot air leaves through exhaust vents near the ridge and air is pulled in at the eave to replace it. ARMA, the shingle trade body, calls it the chimney effect. Attic heat ages the covering from below while the sun works on it from above, and ARMA says venting brings roof temperatures down in a hot climate.
What the code asks for
- 1/150 is the baseline.One square foot of net free ventilating area per 150 square feet of attic.
- 1/300 has to be earned.The exception in R806.2 wants 40 to 50 percent of the required area from ventilators in the upper portion of the attic, at least 3 feet above the eave or cornice vents, with the balance at the eave or cornice. It carries a vapor retarder condition in the climate zones the section names, so ask your building department before sizing at 1/300.
- Openings have a size band.R806.1 sets a least dimension of 1/16 inch minimum and 1/4 inch maximum, and anything larger gets screened inside that band.
Net free area
Net free area is the open space in a vent that air can pass through. Screens and mesh cut into it, so the air path is smaller than the hole. The rating is on the manufacturer's data sheet, and plan check asks for it. Multiply the rated area of one vent by the number of vents and hold that against the attic square footage.
Venting a tile roof
A barrel tile roof will not take a ridge vent the way a shingle roof does. The exhaust goes in as low-profile vents set into the tile field near the ridge, and the intake comes in at the eave under the first course. They get cut and flashed in while the tile is off, so a lift and relay is the cheap time to add them.
Balancing intake against exhaust
ARMA puts intake at 50 to 60 percent of the net free ventilation area and exhaust at 40 to 50 percent, and says intake should never be less than exhaust. Most attics that fall short are short at the intake. NRCA's Professional Roofing reports that a ridge vent starved of intake pulls make-up air from itself and can draw in weather.
Two kinds of exhaust over one attic
Two types of exhaust vent over one attic short circuit each other, and ARMA says combining them goes against the manufacturer's instructions. The air takes the short way between the two openings, and the second one starts working as an intake for weather and debris. The common version on an LA re-roof is a new ridge vent over the decorative gable vents of a 1920s house, with nobody closing the gables off.
The eave is where it usually fails
R806.3 says blocking, bridging and insulation must not block the free flow of air, and that a 1 inch space has to be left between the insulation and the roof sheathing. A house can have soffit vents down both eaves and no air moving above, so the eave gets looked at first. Opening a packed eave back up and holding it open with baffles is insulation work, a C-2 trade on a separate ticket. What a roofer looks for in an attic is on the roof inspection page.
Vents in a high or very high fire hazard severity zone
CRC R806.1.1 sends ventilation openings in a high or very high fire hazard severity zone to the California Wildland-Urban Interface Code, Title 24 Part 7, which replaced Chapter 7A and R337 on January 1, 2026. Sections 504.10.1 and 504.10.2 ask for vents listed by the California State Fire Marshal or tested to ASTM E2886. The Class A fire rated roofing page goes through it vent by vent.
What the warranty says about venting
GAF's limited warranty states that failure to install adequate ventilation is not covered. CertainTeed shortens the term and drops SureStart coverage where it considers the deck inadequately ventilated. A defect in the shingle itself is still covered. Read the warranty for the shingle going on your roof.
What to ask your roofer
- What attic area did you measure, and are you sizing at 1/150 or 1/300?
- What is the rated net free area of each vent, and how does intake split against exhaust?
- Does any old exhaust vent stay open once the new ones go in, and is the eave path clear?
Put those answers in the written quote. The roof replacement page covers the rest of the job, and you can ask for a quote when you are ready. Roofing work in California takes a C-39 license, and any license number can be checked on the CSLB website.
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