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July 11, 2011 10:30 AM   Subscribe

Our attic space is very very hot. We have ridge vents, and two (small) gable vents, but no soffit vents whatsoever because the house (a 2000 sq foot 1960s ranch) doesn't have soffits. Instead, when you look up at the side of the house, you just see the bottom of the roof; there's just no place to install a soffit vent. The AC vents run through the attic. The previous owner put 20" of insulation in, which seems to be keeping things manageable, but I'm sure that we're losing a lot of cooling via the attic. As, again, it is unbelievably hot in there. I've actually been leaving the attic stairs in the garage down when I'm home, with the garage door open, in the hopes that some airflow will result. How can we cool it down? I know that just adding powered fans will do next to nothing as there's nowhere to draw the air from (b/c no soffit vents). Any experience with any new fangled systems? Austin, Texas (so snow is not an issue). The house has stood for 50 years like this, as have all the houses around it, so I know that we don't have to do anything, but I'd like to if there's a reasonable solution.
posted by seventyfour to Home & Garden (18 answers total)
 
The height of the rafters is in there somewhere, even if you don't see it when you look up the wall. Can you submit a photo?

See Bird Blocking
posted by humboldt32 at 10:37 AM on July 11, 2011 [2 favorites]


Larger gable vents ought to be an option. You should probably also insulate the AC ductwork.
posted by jon1270 at 10:39 AM on July 11, 2011


Humboldt32, the roof is actually just like the one you linked to, so I suppose the linked bird blocking could work, although, gosh, it is pretty ugly.

If the gable vents were enlarged, would I be advised to put a fan at the gables to force the air through?
posted by seventyfour at 10:43 AM on July 11, 2011


Sort of ugly, yeah, but that's a pretty standard method. You can fill them with these or similar. Those are copper but you can find cheaper aluminum ones.
posted by humboldt32 at 10:50 AM on July 11, 2011


There was talk of attic heat management on Apartment Therapy recently, and radiant barrier insulation was recommended as a way to cool an attic by reflecting heat away.
posted by illenion at 10:59 AM on July 11, 2011


Humbodt32's pretty much got it. Those holes (or other similar methods) are how you a create airflow for an attic without soffits and is pretty typical construction practice.
posted by LionIndex at 11:00 AM on July 11, 2011


Also, it's good practice to install insulation baffles.
posted by humboldt32 at 11:15 AM on July 11, 2011


There are also some roof vents you can get installed. I'd recommend this Austin company as a way of getting at a radiant barrier & maybe more insulation.
posted by mattbucher at 11:16 AM on July 11, 2011 [1 favorite]


You might also look into evaporative roof cooling systems.
posted by paulsc at 11:36 AM on July 11, 2011


I would install fans in the gable vents with this twist. Install one blowing into the attic and the other (preferably at the other end of the house) blowing out. This is the system, in miniature, that I have for cooling my computer inside a desk cabinet. The constant flow of air from outside will help decrease the attic temperature down to about that of the outside air. I also use this to cool our pantry room with two refrigerators and a freezer. In that case the fans blow out of the room into the attic and then out of the attic into the great outdoors. They are set to come on at 90 degrees, so they aren't on when not necessary.
posted by Old Geezer at 12:00 PM on July 11, 2011


I looked into solar-powered attic vent fans a few years ago, seemed like a cool idea. Googling yields a bunch.
posted by mareli at 12:14 PM on July 11, 2011


Your vented ridge isn't doing much because you don't have soffit vents. A power vent installed in your gable would help. Increasing each of your gable vent sizes to 1/150 of the square footage of your roof would be the code minimum in Canada and would make a big difference.

If you live someplace with lots of sun a radiate barrier applied to the bottom of the rafters inside the attic can significantly reduce attic temperatures. It will however increase roof deck temperatures without proper soffit venting which can reduce the life of shingles.

seventyfour writes "I suppose the linked bird blocking could work, although, gosh, it is pretty ugly."

You could hide the bird blocking behind vented soffit material applied directly to the bottom of your rafters.

And your A/C duct work should be insulated to at least the same rating as your walls. You can buy fiberglass insulation in rolls for just this purpose.
posted by Mitheral at 2:48 PM on July 11, 2011


Do you have turbines on your roof?
(that link is just an example). I've lived in Phoenix and in Dallas, and all the roofs have those for ventilation.
posted by CathyG at 3:41 PM on July 11, 2011


20" of insulation is pretty darn good. Of course, make sure the insulation is on top of the ductwork.

I would probably want to do some testing and calculating and see whether you would even benefit from more insulation. Temperature drop from the ac unit to the wall vents would probably be one way. If the temperature isn't dropping very much, you aren't gaining much heat.

I think, with that much insulation in the attic (assuming it is installed correctly) any efficiency losses you are having will be the result of air infiltration or negative pressure. (IE, the ridge vents are sucking hot air out of the attic, and your cooled air is replacing it.)

If you are intent on reducing the temp in the attic, I would probably figure out a way to install a "return" duct. Somewhere on the north side of the house, cut an opening and install ductwork into the attic so that the hot air exhausted through the ridge vents gets replaced by cooler air drawn in through the vent on the side of the house.

Another option would be to install insulation into the roof rafters, along with a radiant barrier. This might be enough to knock down the heat getting into the attic so that the ridge vents can do a better job of keeping the temp closer to outside air temp.
posted by gjc at 5:08 PM on July 11, 2011 [1 favorite]


Some conspicuous options for soffit vents:

SmartVent by DCI
Cor-A-Vent
posted by tfmm at 5:16 PM on July 11, 2011


Thanks for all the suggestions and info, folks, it is appreciated.

CathyG, turbines are a popular choice in my neighborhood, but my understanding is that they aren't going to do much on anything if there isn't a way to draw sufficient cool air up from the bottom of the roof (which would usually be soffit vents). That's why we didn't install solar powered roof vents (because they wouldn't have anything to draw against).
posted by seventyfour at 7:48 AM on July 12, 2011


I'm not a big fan of 3 things in your picture... gable vents, attic fans, and radiant barrier.

If your roof looks like the one in the picture with the bird blocking, you can put soffits in pretty easily. Just do the bird blocking holes, then add a soffit below it. I like HardiSoffit continuous soffits. Make sure you put baffles in your attic so that insulation doesn't get up against the holes and block the air flow.

Gable vents tend to (from my tests/experience) short-circuit ridge vents. The air comes in the gable vent and then goes right out the ridge vent, leaving the rest of your attic without any air movement. I tend to recommend that people ventilate their soffits excessively, and then put turbines in the peak of the roof. If you're exchanging the hot air out your attic frequently enough, it can't penetrate the insulation and get into the house.

In my experience, attic fans are a big fire risk. They're in a hot dusty environment and aren't maintained all that often. It doesn't take much for one of them to blow out the motor bearings and overheat, or get a wire chewed by a rat, and start a fire.

It's absolutely doubtless that adding a radiant barrier on the inside of your attic will reduce the temperature in the attic, but IN MY EXPERIENCE, the problems with a retrofit installation are legion and I don't feel that it's worth it. The radiant foil can cause your roof surface (typically tar paper and asphalt shingles) to overheat and prematurely age, for instance. I think it's foolish to follow this trend when it's poorly understood and when the problem can be solved with ventilation which IS well understood. I joke that a radiant barrier on the inside of the attic is like putting a tin foil hat on your house. It makes no sense to me to allow the heat into your attic in the first place and try to reflect it back out; the radiant barrier should be on the OUTSIDE of the structure.

NOW, if you're thinking of re-roofing your house with an energy-star rated roofing material, or putting in a reflective roof system that consists of a radiant decking barrier and a rain screen, that's a completely different thing.

Re: Insulation ... it sounds like you're already at R-60 if you have 20 inches (average value of blown in insulation is R-3 per inch), so you're in really good shape there.

Past that -- you haven't said anything about the other "low hanging fruit" for making your house energy efficient. If you are doing all this work in the attic and you still have single-paned aluminum windows and 1960's era doors, then you're doing foolish things. Replace your windows with dual paned low-e windows before you spend any more money in your attic.
posted by SpecialK at 8:50 AM on July 12, 2011 [1 favorite]


I would recommend browsing the Building Science website, specifically searching for articles on roof and attic ventilation.

Honestly, I think adding the bird-blocking is a great idea, as is making sure the house is thoroughly air-sealed between living space and unconditioned attic space. My hunch is that you're fine on the air sealing, though, since I don't think the attic would be quite so hot if you had a lot of conditioned air leaking into it.
posted by rocketman at 8:29 PM on July 12, 2011


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