Venting Attics for Heat Control, or Not?

[Andrew Barss]

I won a house in Tucson, AZ with a crawlspace attic. I had always thought the attic should be vented, so that the heated air from the day's sun would get out fast, and I wouldn't have a pocket of ~150 degree air on the other side of the attic insulation. The insulation is loose fill between the cewiling joists.

I just had an energy evaluation from a licensed company, and they recommend replacing and upgrading gthe insulation (which I knew already), but in discussing the venting issue they recommend against it, on the grounds that their tests should venting or not venting has essentially no efect on cooling costs, when (a) the attic is well insulated, and (b) the living space is very well sealed (so as to prevent air draw into the attic).

I should say it will be a LOT easier if I don't need to install additional air flow in the attic -- soffit vents would be difficult to install, and I have read very mixed reviews on e.g., attic fans (fire hazard, noiuse, effectiveness).

So: Experience? Advice?

Thanks

Andy Barss

[Malcolm Hoar]

Insulate first. It sounds like you're already convinced the current insulation needs an upgrade.

I'd likely pass on the attic vents since you say that will be difficult/expensive to address. However, it's something you could re-evaluate later if you feel the need.

[Don Phillipson]

This point should be easy to verify through the US National Institute of Building Research (Dept. of Commerce) or whatever it is now called: formerly a division of the National Bureau of Standards.

[aemeijers]

Dunno about cooling costs, though unless you have R-999 in the ceiling, that mass of superheated air must be having some effect. But it ALSO cooks your roof deck and shingles. I'm not in AZ, but doubling ceiling insulation cut the heck out of my cooling costs, and doubling the air exchange in the attic cut at least 20 degrees off the summertime temp up there. The hatch isn't hot to the touch at midnight any more.

[Fatter Than Ever Moe]

You won a house with not enough insulation? I'd sue for the insulation, and have the lawyer also sue for attic venting while you're at it. And if the garage didn't have a car in it.... we'll it should have, tell the lawyer to put on the list also. Seriously,

[clare]

I wouls DEFINITELY vent the attic , particularly if it was anywhere but Tescon. Moisture bei g the big problem (which is why I say anywhere but Tuscon). In Arizona it MIGHT not be an issue. Here in Ontario it most definitely IS.

[Mark]

i'd go with the best insulation you can afford and go with PASSIVE venting that uses the prevailing winds in your area,

install one opening on the upwind side and one on the downwind side and let the wind do it's thing ..

Mark

[Frank]

I agree that I would only use passive venting. Years ago I put in a thermostatically controlled attic fan and it did not seem to make much difference and wore out in a few years. My neighbor had one that actually caught fire and who knows what would have happened to family late at night if other neighbor had not seen the flames.

[HeyBub]

Huh?

Fact #1: The cooler you can get the attic, the less A/C you'll need. (plus less degradation on the roof deck and roof itself).

Fact #2: You can't have too many soffit vents.

[Shaun Eli]

I put in an attic fan and it made a lot of difference. 15+ years, it's still working.

It is simply a fan up against the vent on one side of the attic- the fan's bigger than the vent (vent is a wide triangle) so it's not even that efficient. But it helps a lot. Had R-30 when I put it in (now have R-60 in most of the attic- attic is now about outside air temp, used to be really hot up there.

If you don't have a big vent, you can always have a contractor cut a hole in the roof and put a fan there...

[hrhofmann]

If you can get your roof replaced for free, then don't worry about attic temps. But if you value your roof, you will try to keep the attic temps as cool as possible, which means venting as much as possible. Of course, it also helps downstairs.

[trader4]

Agree. He could put a cheap digital thermometer from Walmart or HarborFreight that records high and low temp in the attic and see how hot it gets. Adequate ventilation also means the attic will cool down a lot quicker at night, instead of having a lot of hot air trapped there. Even with lots of insulation a significant amount of heat will still get in. And as you point out, those high temps aren't helping the shingles or roof decking.

Another possibility is adding a radiant heat barrier under the rafters.

[norminn]

Licensed? For what? Fire them. Then get estimates from a couple of decent roofers and ask them about venting. Wouldn't hurt to do a little research online for roofing products, and read their installation info.

What ventillation exists now? Got ridge vents? There is a formula (Google it) for calculating the ventillation needed, depending on the area of the ATTIC SPACE, not roof area. A photo might help.

[Andrew Barss]

:>I should say it will be a LOT easier if I don't need to install additional :>air flow in the attic -- soffit vents would be difficult to install, and I :>have read very mixed reviews on e.g., attic fans (fire hazard, noiuse, :>effectiveness).

: Tile roof? I have large gable vents (2), soffit vents and thick : blown-in insulation (Nevada) and it still gets hot up there. In lieu : of electric power vents, perhaps a solar powered unit on the gable : vent.

Nope, asphalt shingle roof, over softwood (probably pine) sheathing. There are two of what pass for gable vents here -- meaning there are a few brick-sized gaps on either end of the house, toward the top of the peak. I think if I were to utilize them I'd need a larger hole on each end, which means getting a decent mason who knows what not to remove, and they're thin on the ground here.

So it seems like I have these options, after blowing in the insulation (we investigated getting foam sprayed on the underside of the roof, which is the approach I'd like to do, but the price is prohibitive), and after completelty sealing the ductwotk (it's in the crawlspace) and ceilings to prevent airflow from the cooled living space up to the attic:

(a) seal the attic completely.

OR

b) Installing a ridge vent along the length of the house, and figuring some way to get outside air into the crawlspace. Soffit vents are pretty much out (the roof rafters end right on the header plate sitting on top of the brick walls (common feature of c. 1940s housebuilding here), so soffit vents would require removing the current fascia, attach rafter extensions, building out the roof, closing the extensions off with new fascia and proper soffit boards, and putting in vents.

I have seen mentioned (but not in detail) intake vents that can be mounted low down on the roof (near thre bottom of the attic air space, right above the unsulation line). Anyone know what they're called? This would get the day's heated out out faster, and would (I think) lessen the heat load above the new insulation in the attic.

c) Installing a powered (possibly solar-powered) attic vent fan.

-- Andy Barss s

[Andrew Barss]

: You won a house with not enough insulation?

Heat cooked the spelling portion of my mind there for a sec!

: Seriously, :

Thanks very much for the link. A quick skim of it suggests it may be fine to not vent, but I will certainly read it more carefully later today.

-- Andy Barss

[Andrew Barss]

: Fact #2: You can't have too many soffit vents.

Well, in this house, unless I do something drastic I can't have ANY soffit vents! (See other post on how the roof doesn't overhang the walls).

And ... the soffits would be below the insulation, do I'd need to get an airflow channel for every vent, otherwise they'll get plugged up with insulation.

-- Andy BArss

[Fat-Dumb and Happy]

The most cost effective insulation would be blown in cellulose insulation. If the there is knob and tube wiring though it is a no no until that is addressed. Also any recessed lights fixtures that might have been put in.. My old house, I put some good sized gable vents in it and called it good. The old 20/80% rule, 20 percent of the effort gets ya 80% of the results. I try to live by that rule..... it's 108 degrees here today.

[HeyBub]

Without soffit vents - or their equivalent - any attic fan or exhaust mechanism will be pulling conditioned air from the living space.

"Nature always finds a way."

[trader4]

I agree. Given the restrictions, I'd say decent size gable vents at each end of the attic, with a fan blowing out on the end with the best probablility of blowing air with the wind.

[D.A. Tsenuf]

Run a couple couple of lengths of copper pipe through your attic to a heat exchanger. Use all that heat for a water heater or for heat when the nights are cool.