Roof turbines, are they a good idea?

I have a small old two story house, and the top floor gets very hot during the day. I'm thinking of installing one or two roof turbines, and also am considering putting some insulation in above the ceiling, under the roof (I'm sure there isn't any right now). I'd like to hear some opinions about these ideas, and would appreciate any other suggestions. I like the idea of the roof turbines because they don't require anything but a little wind to operate.
John
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jbclem wrote:

First I suggest you make sure the attic is vented according to the local norms. Old homes often have insufficient ventilation. Just adding turbine vents will not fix it. You need to have a way for fresh air to get into the attic (usually soffit vents) and a way for the hot air to get out, usually ridge or other vents placed high on the roof. In most areas this is sufficient.
Insulation is a must, and even if you have some now, more is always better. You also want a vapor barrier. What makes a good vapor barrier depends on what your local weather is like (where do you live?)
Turbines are for those few areas or construction situations were standard static venting does not work well. If you do decide on turbines, I strongly suggest you get top quality units as the cheap ones are subject to sort life, leaks and noise.
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Joseph Meehan

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jbclem wrote:

during the day.

considering putting

isn't any right

appreciate any other

require anything

I suggest you look at the Building Science Corporation web site. It has * researched * information on venting and related issues. Climate is an important part of deciding whether or not to vent an attic. TB
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Convection from hot spaces drive them. Our garage went from 10 above adjacent patio to 10 below when the turbine was put in during reroof.
wrote:

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That's nice to know...if the convection drives the turbine than it would actually turn without any wind. I like that 20 deg drop you got, that would be very nice in my case...although your turbine was probably vented the entire garage, not just the roof-celing area.
John

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anything
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jbclem wrote:

What I wonder is if the convection is enough to turn the turbine, why bother with the turbine when you already have the strong convection?

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I read a project report once that said convection venting was more efficient with a "tall" vent pipe than with a turbine. I believe the vent pipe in that case was dark coated for solar heat absorption, thus aiding the flue effect (along with some extra height).
Bill

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On Tue, 24 May 2005 02:23:00 GMT, "bill a"

My impression was that the point of a turbine isn't to be efficient, although on a windy day, it helps. The point of a turbine is to keep crap (and vermin) out of the vent pipe. Wasps don't like it when their house moves.

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But turning them and the outgoing air takes energy, which slows that air, compared to a gable or ridge vent or thermal chimney with the same area.
Nick
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The 20 drop IS appreciated almost daily. The outrush of hot air when the roofer cut the hole was impressive! Had his not oo long hair waving for a few seconds. Not ceiling in the garage and mostly have a door open for ease of access and replacement air as needed. Got the $20.00 special from HD as that was all they had. No lube or problems since installation about 10+ years ago. No planning just a thought as they were reroofing.
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nospambob wrote:

Which is a really good indication that you did not have enough high vents to start with. Likely any added vent, including passive (ridge or any non-powered roof vent) would have done very well. The turbine vents can add some additional venting when there is a wind.

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I've seen the turbine turn when there was NO wind moving the leaves outside though it was warm inside the garage. Turbines DO NOT NEED A WIND TO TURN. Our garage didn't have any vents as built. Find the definition of "convection" which is what warmer air rise.
On Tue, 24 May 2005 17:44:18 GMT, "Joseph Meehan"

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nospambob wrote:

No they don't need wind to move. The natural flow of warm air will cause them to turn, but that turning is actually slowing down the movement of the air, you would get more movement if you removed the part that turns.

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I agree with you about the value of the turbine component. I think they are primarily for the entertainment of the homeowner. :)
Bill

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I didn't mention but this house is in Southern California, just outside Los Angeles in the SM Mountains, an area called Topanga Canyon. I will check the old vents and also look to see if there are soffit vents. I know there is one high vent at one end of the house, the other end is two stories up and will be harder to check.
I plan on replacing the ceiling in the living room and that would be a good time to add insulation. I didn't think of the vapor barrier, what exactly would it do? Is there a specific kind of vapor barrier I would need. Also, would someone suggest the rating of the insulation I would be looking for(thickness, R-? rating). I don't think there is much area underneath the roof, I've only seen it once and I believe it was about 2 feet at the peak. The celing in the living room doesn't start at the top of the wall but rather is angled for about a foot from the walls and then becomes horizontal. That angle is following the angle of the roof rafter(joist?) and I'm wondering if it may be covering up the place where the soffit vents would be.
John

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