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Gable and ridge vents literature

John Helder | Posted in General Questions on

Hello,

Should I install a ridge vent with gable vents and without any soffit or other eave venting? The attic space is currently vented with a gable vent on each end (no fans or other active). The house is a gambrel-style / barn-style / dutch colonial so there is also unvented roofing shingles around the 2nd floor. The two areas (steep shingles around 2nd floor and gradual above attic) are not connected, save any framing gaps between the two.

I am looking to replace my roof and the contractors I received quotes from all want to install a ridge vent, but no soffits (since there is no traditional place to install). One did specify the ridge vent would be an external baffle unit, but the others were vague as to what would be installed.

I have seen some of the options for sheathing-mounted venting options, but have not found any contractors familiar with the product.

Is there any literature on the gable-ridge venting combination? I have seen lots of articles on how venting should be, but nothing on if this combination is an improvement/detriment compared to just the gable vents?

The house is located in Zone 4a, just north of Washington DC and south of Baltimore.

I’m a longtime reader of the site and have always been impressed at the responses compiled for the digest articles.

Thanks.

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    John,
    Are there and signs of moisture problems in your attic (mold on sheathing, for example)? If your attic is dry, don't worry.

    Attic ventilation is an overrated measure. The theories expressed on building sites about the value of attic ventilation are based on opinions and old stories, not science.

    If you want to prevent attic moisture problems, the most important step you can take is to reduce air leaks through your ceiling.

  2. John Helder | | #2

    Martin,

    No, there are no apparent moisture issues. [No mildew, mold, or sagging sheathing. Just some dark brown trusses reminiscent of extreme heat on the more southernly exposure.]

    By your statement, is it correct that the addition of a ridge vent would provide neither benefit nor impairment? From a 'comfort' or 'energy-efficient' standpoint, I agree with you. Attic temperature will not affect the conditioned envelope. Does this argument extend to asphalt shingle performance/durability?

    I have caulked all the ceiling boxes and have a sealed cover for the attic hatch, but these have only been part of the house for about a year. The insulation minimal/original R19 fiberglass batts and the plan is to supplement it with blown-in insulation after the roof is complete. However, this means that the roof has been partially conditioned all these years thereby moderating the temperate extremes of the roof (via leaking conditioned air). Sealing all this leaking air seems good, but this alters the dynamics of the attic and I cannot tell if I am being penny wise (minimizing the continuing/variable costs), but pound foolish (increasing the capital expenditures by reducing the life of the roof).

    Thank-you.

  3. GBA Editor
    Martin Holladay | | #3

    John,
    Q. "Is it correct that the addition of a ridge vent would provide neither benefit nor impairment?"

    A. If I were you, I would install a ridge vent in conjunction with the new roofing work. It's easy enough to do, doesn't cost much, and may provide some minor benefit.

    Q. "Attic temperature will not affect the conditioned envelope. Does this argument extend to asphalt shingle performance/durability?"

    A. Studies of asphalt shingle longevity are hard to conduct, but it's safe to assume that temperature affects shingle durability to some extent. There are two twists to this issue: attic ventilation doesn't lower roof sheathing temperatures as much as ventilation advocates assume; and the color of the shingles and the orientation of the roof matter far more (when it comes to shingle temperature) than the presence or absence of attic venting.

    You can't change the orientation of your roof, but you can choose the color of your shingles. If you want cooler, long-lasting shingles, choose white shingles. In any case, whatever color of shingle you choose, I wouldn't worry too much about attic ventilation.

    You seem to be hypothesizing that your ceiling has been so leaky over the past few years, and your air conditioning system is so powerful, that leaking cool air during the summer months may have been air conditioning your attic and lowering the roof sheathing temperature. I find this theory far-fetched and unlikely. While ceiling leaks have certainly raised your energy bill, it is unlikely that the escaping cool air has been significantly cooling your roof sheathing.

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