Roof ventilation ideas
I’m trying to add attic ventilation for my whole house fan, as the manufacturer states that I need a total of 4.4 sq. ft. of free air. I currently have gable vents, but they’re located right above a window and the attic air gets sucked right back into the house (even when the window is closed, to some degree, and I’d like to open that window anyway). So I’m thinking of sealing off the gable vents and getting all the ventilation from the roof.
One roofer suggested eyebrow vents, but this would amount to far less than the 4.4 sq. ft. So I did my own research and discovered that O’Hagin makes a vent that allows just over 1 sq. ft. of free air. So I could install 5 of them and meet the requirement, but down the road I may want to add a foam roof. So I called a foam roof installer who suggested that I should install a taller vent instead, so the foam would be able to go around it. He suggested an 8-inch or 10-inch 024 top-to-bottom vent, but I have no idea what he’s talking about.
Any suggestions on how to add this ventilation? Are there better options than the O’Hagin vents, especially in consideration of a long-term plan?
I have a tar & gravel roof with a 2/12 pitch, at least 20 years old. In addition to the gable vents, there are soffit vents around the house. The soffit vents total 1 sq. ft., minus the double insect screens. I live in the SF Bay Area.
Thanks very much.
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Replies
Robert,
If you are planning (eventually) to install rigid foam or spray foam at your roof line, then you need to install the type of whole-house fan that is designed for an insulated roof assembly. These fans sit above the roof.
Here are links to two web sites that offer the type of fan you need:
http://www.atrendyhome.com/romowhhofano.html
http://www.tamtech.com/TC1000-H-Solid-RoofWall-Home-Ventilator-Brown_p_112.html
If you install this kind of fan, you don't need any additional attic vents, because the fan blows air directly to the outdoors. And you will be ready for the future (when you create an unvented conditioned attic).
Thanks Martin, and apologies for that delay in my expression of gratitude. I'm just very frustrated. I've already installed a QuietCool fan that blows air into the attic, so it requires ventilation. And I've already thrown a lot of money at it, for some pretty meager results, so it's sounding more and more like it was a mistake.
If I get a foam roof, does that mean that it should not be vented? (It didn't occur to me that it might be better to keep the outside air from ever entering the attic, if the roof itself is insulated.)
And does a foam roof negate the need for attic insulation? I was about to spend almost 3 grand to have the attic on the front end of the house sealed and insulated. But I can get a foam roof for 8K, and that would include the rental unit in back. So I wonder if that's a better long-term strategy.
Thanks again.
Robert,
Q. "If I get a foam roof, does that mean that it should not be vented?"
A. Yes. If you install rigid foam on top of your roof sheathing, it means that you have decided to convert your vented unconditioned attic into an unvented conditioned attic. You never want to have any ventilation on the interior side of your insulation layer, or else the moving air will defeat the purpose of the insulation.
Q. "And does a foam roof negate the need for attic insulation?"
A. Not exactly. The foam roof is attic insulation. When you install rigid foam on your roof, you are moving the insulation layer from your attic floor to the roofline.
There are several ways to do this. Read the following articles to understand your options.
Creating a Conditioned Attic
Insulating Low-Slope Residential Roofs
Great, thanks Martin. Lots of useful information especially in the second article, including links to even more. Very helpful.