Are turbine vents (aka whirlybirds) useful for attic ventilation?
September 24, 2012 5:46 PM   Subscribe

Are turbine vents (aka whirlybirds) useful for attic ventilation?

I'm considering installing a couple of turbine vents, but am finding very conflicting information about whether they are of any practical use or not. Most of the opinions I find seem to be anecdata or amateur speculation, with very little objective fact or research.

Specifics of the house are:

- tiled roof with foil sarking (reflective insulation) directly underneath, which prevents any air circulation through gaps in the tiles.

- insulating batts directly on top of the ceilings (yay government!)

- no soffit or ridge vents that I know of, and no gables so no gable vents either.

- the intention is to use the attic space for storage (eg out of season clothes, camping gear, tax records, all that kind of stuff)

One point people make often is that if you have decent ceiling insulation, lowering the summer temperature in the attic cavity has negligible effect on the temperature within the house itself. This is the one point that seems to be backed up by objective studies.

Given this, is there any benefit in ventilating the attic? Is it normally just to get rid of stagnant air, and thereby prevent mould & pests? Are there any other considerations I might be missing?

Also, are whirlybirds the best option for retrofitted ventilation? Around here, they're the de rigeur solution sold by all the attic conversion companies...
posted by UbuRoivas to Home & Garden (12 answers total) 1 user marked this as a favorite
You want your attic to be vented. Depending upon where you are, you either want to allow hot air to escape in the winter to allow heat to escape, preventing ice dams, or you want moist warm air to escape to allow the stack effect to work, lowering the cooling load on the house and reducing the risk of mold.

I'm a huge fan of cor-a-vent ridge systems, especially in New England, but the most appropriate venting solution will vary depending upon where you live.
posted by ellF at 5:51 PM on September 24, 2012 [1 favorite]

For clarification: I'm in Sydney, Australia. It never gets below freezing. Winter nighttime lows might be 5C /41F & summer daytime highs up to about 40C / 104F but more typically around 30C / 86F, but with high humidity often 80% or above.
posted by UbuRoivas at 5:57 PM on September 24, 2012

I once lived in a rather well insulated house, but we definitely noticed when the (electric) attic fan quit working. It was replaced with a whirlybird and all was better. Supposedly they don't work as well as a powered vent, but it did some good for us.
posted by wierdo at 6:48 PM on September 24, 2012

Vents need a place to pull air from -- if you have no soffits and no gables, the danger is that you will pull air from inside the house instead, which isn't good for keeping your house cool.
posted by Forktine at 6:56 PM on September 24, 2012 [1 favorite]

Forktine - yeah, I was thinking that as well. There are actually soffits (eaves) just no vents in them (yet?).

Instead, there are vents high up in the walls, through double brick connecting inside to outside (originally to replace air burned in fireplaces, back in the day).

The gaps between the double brick open directly into the attic my hypothesis is that if air follows the path of least resistance it will draw in from the outside, up about a foot in the gap between the bricks, and into the attic that way - so long as the house is closed up & reasonably free of easy draft access under doors etc.

I think a smoke (incense) test should determine whether air is being sucked from inside, and if so I'd consider sticking some soffit vents in.
posted by UbuRoivas at 8:22 PM on September 24, 2012

haha, we are renovating our recently purchased house, and had a conversation with the builder this week about this very thing.

For our house, he recommended it from a ventilation (not temperature) perspective; esp as it seems the rangehood and bathroom go directly into the ceiling cavity and there's nowhere else for the moisture to go.
posted by smoke at 9:23 PM on September 24, 2012

A highlight of my Sundays is watching Holmes Inspection :) So while I don't know for sure, here's things I always hear on the show:

Wood needs to breath; that includes the wood under your roof. Since it can't breath from the outside, it has to breath from the attic. And if you don't put proper venting under the soffits, then you won't get proper airflow through the vents, and the wood won't breath.

Wood that doesn't breath molds. It rots. I notice you said 80% humidity: mold is certainly a concern. Is it already black in places? You could have an existing mold problem.

Also, if you aren't going to run HVAC through a major space (aka: your attic, garage, cold room in the basement) then as a rule it's an outside space, not an inside one. And outside spaces need to be at the same temperature as the outside (duhh). Without proper roof venting, this can't happen.

So I'm sure Mike Holmes would say: cut proper vents in the soffits. Get baffles if you need them to get air from the soffit vents to the attic space (insulation otherwise can block the path).

Also, Holmes doesn't like whirlybirds, but I don't remember why. He always just has plain old, critter proof vents installed.
posted by sbutler at 9:54 PM on September 24, 2012

The Weekend Woodies/Homies on 702 really promote then whenever it comes up. We've got one in a house similar to how you've described yours. I have no idea what life would be like without it as it was installed before we bought the house.

A nice, and unexpected, feature is that they allow some light in too.
posted by taff at 10:13 PM on September 24, 2012

I hadn't heard of either Holmes Inspection or Weekend Woodies (on Australian Broadcasting Corporation radio 702) but they both sound right up my alley right now - thanks for the tips!

Looking at a model with a clear perspex top that doubles as a skylight - so yeah, letting light in is a collateral benefit. Hm, the money saved in not getting a sparky in to install a light up there almost pays for the whirlybirds...

posted by UbuRoivas at 10:48 PM on September 24, 2012

Canadian roofs used to have a lot of whirlybirds through the 80s and 90s. Roofers have been ripping them out for the past 15 years because they all squeeked. That high-pitched eeek-eeek-eeek was the sound of suburbia in my youth. My dad went so far as to put a grease bearings in his, but that just meant one of us had to climb onto the roof with a grease gun every year.

Most Canadian roofs now have high-flow static vents like these. They draw by cross-wind and apparently work even better than the noisy old turbines.
posted by bonehead at 11:05 PM on September 24, 2012

Agreeing with Forktine, the vents you're describing allow air out, but you need that air to come from somewhere and that somewhere should not be the living area, especially if you have air conditioning; that air is expensive.

Wood needs to breath; that includes the wood under your roof. Since it can't breath from the outside, it has to breath from the attic. And if you don't put proper venting under the soffits, then you won't get proper airflow through the vents, and the wood won't breath.

Wood that doesn't breath molds. It rots. I notice you said 80% humidity: mold is certainly a concern. Is it already black in places? You could have an existing mold problem.

I've seen the show too and am generally impressed, but this business about wood needing to "breathe" is wrong. Wood needs to stay dry. Wood that is dry does not rot. Ventilation can help prevent rot by removing small amounts of excess moisture, e.g. from a tiny roof leak, but that's not a primary reason to do it.
posted by jon1270 at 2:37 AM on September 25, 2012

Thanks for the answers, everybody. I think it's pretty clear now that I need to address the ventilation situation, because since the sarking was put in there's been minimal airflow up there.

Ventilation would be the main objective. The house itself apparently won't feel much of a change as long as I ensure that warm air in winter isn't being drawn out of the living spaces, or cool air in summer, so I'll keep an eye on what the existing wall vents are doing. Anything stored in the attic would probably benefit from not being roasted in summer, too.

As for the Canadian situation (and I understand that Holmes Inspection is a Canadian show) I had read elsewhere that whirlybirds there suffer a bit from ice. Supposedly they'll stay squeak free as long as they're not out of alignment, but ice formation can throw this out. Certainly, they seem to be far & away the market leaders for ventilation down under, and I can see at least half a dozen within a stone's throw of my backyard & there's not a squeak from them, so it appears that the squeaking issue isn't a problem here....? Worst case (as they slot in place of a single standard roof tile) is that I might need to replace them with a more passive kind of vent some years down the track, which would also be designed to the same dimensions.
posted by UbuRoivas at 2:46 PM on September 25, 2012

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