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Community and Q&A

What is better – roof vents without soffit vents or change to an unvented assembly?

Sean McLoughlin | Posted in Energy Efficiency and Durability on

I’m back after having met with the architect and asked about the soffit venting.

We’re designing a home in Southern California (hot dry / mixed dry climate) – the architect is calling for an unconditioned attic, insulation on the attic floor at the ceiling, but fire codes in this wildfire prone part of the world now ban soffit vents of any kind, effectively requiring boxed or sealed eaves. The architect has drawn in a bunch of roof vents that apparently are permitted, but it makes me wonder how effective those can actually be, if they’re halfway up the roof, and they’re not every sixteen inches.

Might we be better switching to an unvented roof assembly? We are already planning on using radiant barrier sheathing on the roof sheathing to reduce the attic temp in summer. Could we put 2 inches of poly-iso foam on the inside of the roof rafters and ditch the vents?

Most years, we get only 4-5 nights that dip below freezing. But I know that unvented roof assemblies need to be designed not to accumulate moisture that can condense.

Thanks in advance.

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Replies

  1. Danny Kelly | | #1

    I'm not exactly sure what you mean by clipped soffit but this may work. Since you say "virtually no soffit" does that mean that there is some soffit? As long as you have a 1" minimum soffit and a fascia boards you can install Cor-a-vents, strip vent - can install directly behind the fascia board if you want or behind the bedmould/crown mould if you do have a small soffit.

    http://www.cor-a-vent.com/s400.cfm

  2. Keith Gustafson | | #2

    They also make vented drip edge

    It would seem to me that overhangs would be useful in a sunny climate, no matter the pitch.

  3. GBA Editor
    Martin Holladay | | #3

    Sean,
    There really are few reasons to vent an unconditioned attic, especially for those who don't live in a climate subject to ice damming, as long as the following conditions hold:

    1. Your builders does a careful job of air sealing the ceiling plane. This should be verified by the use of a blower door.

    2. You have deep insulation on the attic floor, including full-depth insulation at the attic perimeter -- a design that usually requires raised-heel trusses. This insulation should, of course, meet minimum code requirements, although above-code levels of insulation are always better.

    3. You plan must be acceptable to your local building official.

  4. Sean McLoughlin | | #4

    Thanks Martin. The attic/ceiling will be R38, so I'm really just trying to figure out how we keep the attic itself from becoming hotter than the outside air )because it will have ducting running through it and it will be used for storage, so I don't want things getting cooked up there.

  5. GBA Editor
    Martin Holladay | | #5

    Sean,
    If you are designing a new home in a hot climate, why are you planning to put your ducts in an unconditioned attic? It sounds like you need a new architect.

  6. Sean McLoughlin | | #6

    It is standard practice out here, and as long as the ducts are R8, it complies with California's energy efficency requirements. The primary argument made by the architect and the builders we've interviewed is that the modest loss of cooling by running ducts through the attic is less than the additional load that conditioning all that air within the attic would impose.

  7. TJ Elder | | #7

    Sean,

    There was a time in this country's history when you could own slaves without running afoul of current and local ethical standards.

  8. James Morgan | | #8

    I have to ask: is a Cape Cod a climate-appropriate format for a home in Southern California?

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