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Community and Q&A

Fixing a Poorly Vented Roof in a Hot Climate

vreiner | Posted in Energy Efficiency and Durability on

I live in Los Angeles, climate zone 3B/3C (or California Climate Zone 9).  I have a 6:12 pitch stick-framed roof with asphalt shingles. The attic is very poorly vented with 2 passive vents on the northeast side, no ridge or soffit vents and no gables (roof is pitched all 4 sides). Soffits are about 18″ deep. The HVAC system is in the attic, which is also used for light storage. Attic temp of course skyrockets in the summer.  There is significant tree cover on the southwest side and some cover on the southeast side but house is exposed to direct sun in the afternoon.

My goal is to improve comfort and reduce HVAC load.  My plan is to air-seal the ceiling and improve insulation significantly, because it is currently about 2″ of old rock wool between the ceiling joists. I want to increase to R30-38 with ~12″ of blown in cellulose or fiberglass.  I’m open to other ideas for ceiling insulation.

I have several questions.
A) Should I seal the attic completely and make the attic “conditioned” space OR improve venting significantly by installing soffit and ridge vents?
B) should I insulate under the roof deck/between rafters, regardless of whether I go vented or sealed?
C) If I am sealing the attic, spraying closed-cell foam between the rafters seems to be the right choice, but I am open to advice.
D) If I am venting the attic, using unfaced batts or open-cell foam with an air gap between the insulation and the roof deck have both been mentioned online.  Skipping the insulation and installing radiant barrier fabric on the rafters has also been mentioned.

All the info I’ve found is regarding new construction, and not much on retrofitting this less-than-ideal venting situation, in my climate.  Insulation contractors just want to sell me whatever their most profitable product is.  Ideas, suggestions please?

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  1. user-6184358 | | #1

    I am in San Diego County - I air sealed the ceiling then thru the big box rented a blower machine an installed 12" of cellulose it made a huge difference. All for around $500 plus my time. The attic venting is for moisture issues.
    You should install code attic venting. You can install new better insulated and air tight duct work & bury the ducts in the ceiling insulation. I don't think spray foam is a good material for your project. Look up spray foam problems.
    You likely have a gas furnace for heat - that makes it problematic for the sealed attic approach.

    1. vreiner | | #2

      you're right regarding the furnace. I should have considered that, although combustion air can be ducted from outside. I have been leaning toward sealing the attic because sealing up those two roof vents is so much less work than cutting a ridge vent and installing 20 or so soffit vents, plus better for my stored items (which is vital for me due to very little storage space inside the house). If I had gables on this roof venting this attic would be so much easier!

    2. exeric | | #3

      I have to agree with Tim here. Do the correct thing and vent the roof to code or as close as one can get it. Cellulose above an air sealed ceiling is the cheap and most effective way to insulate the conditioned space of the home. Also better for the environment. I have a home very similar to yours in California and its way less important here than in the East to keep the HVAC in conditioned space.

      One thing I would definitely do as long as you are doing the rest is this: Staple a perforated radiant barrier to the underside of the rafters. It is amazing how much they cut down on heat penetrating the attic. I know because I did it on my own home. You won't regret it and it will definitely help your HVAC equipment perform better in summer.

      1. vreiner | | #4

        Thanks Eric. Can you recommend a radiant barrier product?

        1. exeric | | #5

          It's honestly been so long that I installed it that I don't remember the manufacturer. I think that they are probably all very similar. I would just go with any of the big names and make sure it is perforated to allow moisture migration through the roof venting. Definitely avoid all the manufacturers that have air bubbles as a feature that are claimed to act as insulation. They don't and they are a scam.

  2. vreiner | | #6

    I have 2 other concerns about vented attics: A) embers during a fire entering the soffit vents and B) insects esp. ants and termites. I understand I can line the soffit vents with screening but that just further reduces the airflow through the vents, and wouldn't that require regular cleaning? Spiders in particular would be drawn .to spinning webs there due to the airflow.

  3. exeric | | #7

    There is one other reason to have a roof that is properly vented, especially in many California climates. If I'm not mistaken LA has cool temperatures at night most of the time in summer. That means you could install a Whole House Fan. They operate by opening windows and pulling air from the outside at night and blowing it out through a ceiling vent. That pressurizes any hot air left in the attic from the previous day and blows it out through the vents at the top of the roof. So you get a night time flushing effect.

    It definitely only works though if you have adequate roof venting. It will cut down your cooling utility bill if you had one and used it. Outside noise, low security, and environmental factors such as high outside temperatures and humidity, decrease the benefit of opening windows at night. I have one and use it at night. My electric utility bills, at least by my utility's reckoning, are about 30% below even the most efficient similar homes in my neighborhood in summer.

    I can't speak to pest and burning ember infiltration through vents. Hopefully someone else more knowledgeable can.

  4. user-6184358 | | #8

    They make special vents that are Wildland compliant. Ask the building dept if you are required to install them. As for insects, the vents have screens, that should be cleaned as a maintenance item for any house.
    With the furnace - you would need a direct vent furnace, the duct for combustion air in a old school drafted furnace defeats the sealed attic. How old is you furnace? Do you have AC?

  5. vreiner | | #9

    Furnace is about 25 years old, works well, and does have AC. I guess I could see if there is a direct vent kit for this unit.

    The vents that I bought did not have insect screens. I'll check out the wildland compliant vents! didn't know there was such a thing.

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