Question on Adding more Wirley Birds
timby
| Posted in Energy, Heating & Insulation on
We are getting a new roof because of hail damage(insurance claim). One of the roofers asked if we wanted to add any additional Wind Turbines.
My question is how effective are wind turbines and would adding additional ones would vent my attic more efficiently? I currently have 2 for a nearly 2500 sq ft home in the Dallas TX area.
Any suggestions other than having vent-a-ridge installed (insurance will not cover).
Thanks
Replies
Venting standards are for about one sq ft of vent for each 150 sq ft of living space in the house.
That is one foot in at the soffits and one foot out at the ridge or other - like the whirlybirds.
I would not mix whirlybirds and ridge vents. use one or the other.
Without venting fresh air in at soffits, the ridge or other will be restricted in what they can do to such air out at the top. having it unbalanced that way usually means that the conditioned house air will be sucked up into the attic.
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PiffinI just went outside and counted. We have 26 9.5" x 19" soffit vents. I'm not sure how the vents are measured (outside to outside or inside dimensions). If I'm to use your figures of 1 SQ FT per 150 SQ FT of living space then I should have nearly 13.3 SQ FT for the entire 2000 SQ FT living space. Each of my existing vents comes out to nearly 29 SQ FT. I question whether the existing 2 whirlybirds are enough exhaust or if another 2 vents would be better. We have such high temps in the attics down here and I'm sure when Fox & Jacobs built these homes they didn't include proper practices concerning venting. However, since I have the chance to add additional venting at a reasonable rate I would like to take advantage.Am I missing something? Also, how much heat does a typical whirlybird exhaust (CFPS)?Thanks
how much heat does a typical whirlybird exhaust (CFPS)?
First CFPS would be air movement, not necessarily heat movement.
Now, you're probably not going to get any sort of exact answer. If the wind's not blowing, the turbine is probably not spinning much, so the CFM is going to be no more than a standard roof vent of the same size.
If the wind's blowing, the turbine's sucking out more air, wheather it needs to be sucked or not. Could potentially lead to conditioned air being pulled from the living space.
Turbine's do work, but my experience says a balanced soffit/ridge vent system works best in most cases.
I've noticed certain products get used more in a certain local sometimes simply because they're readily available, not because they're the best solution. One of my competitors installs turbines on every house he roofs. He sells them hard. He's got a barn full of them, because he bought a semi load at a great price. http://grantlogan.net/
But you all knew that. I detailed it extensively in my blog.
I live in Plano.
Try removing one of your soffit vents and seeing what the actual cut out is.
I added more vents and also enlarged the small cut out hidden under the original vents.Do the ridge vents and dump the "whirlybirds".Pete
However, since I have the chance to add additional venting at a reasonable rate I would like to take advantage.
Except the insurance company is only forking over for "what was there."
Really what you need is to pull all of the soffit out and replace it with continuous vented soffit. Since F&J built it, you need to do that to be sure each rafter bay actually approximates a ventilation path into the attic (F&J in the mid cities was discovered to have just screwed those square vents over 3" holes, or no hole at all in some cases). Then you need a ridge vent to match all that soffit vent.
But, what you will find is that, like leaving the windows cracked open on your car, you'll only see a 5-8º decrease in attic temperatures. At least in Dallas, that air will only be in the 30-45%RH range--awfull, but not like down here in southern Texas.Occupational hazard of my occupation not being around (sorry Bubba)
Been meaning to ask you what you do with your old scuba gear at the end of the summer when you get to shuck it and start breathing air again instead of water.
They can't get your Goat if you don't tell them where it is hidden.
what you do with your old scuba gear at the end of the summer when you get to shuck it and start breathing air again instead of water.
Well, quality gear lasts year in, year our (especiall 3-band hats) <g>
Actually, it never really dries out here. From mid-November to March this last year, there were exactly 6 days with humdities under 20% (couple of those were 6%).
Only about 175 miles (crow flies) to the Gulf of Mexico, and with a major river (Brazos) on the est edge of the county, and a minor river (Navasota) on the east. Plenty of moisture, and the geography of riverine valleys to concentrate it.
Gets tricky, too--it's damp enough here to have to/want to keep track of absolute verus relativehumidity.
For instance, it might sound good that the RH has gone from 61% to 45% in the last three hours. It's gone from 86º to 94º in that same time, too. Dew Point has gone from 71º to only 69º--which is why the Heat Index is a lovely 99º (up from 91º at 1100). It's not pleasant outside--if still just tolerable in the shade, idle, when the breeze deigns to blow . . . Occupational hazard of my occupation not being around (sorry Bubba)
Unless you have clean screen only soffit vents, you can reduce your figure there by a good 40%, but sounds like you have enough soffit venting if the pathways are not filled by insulation.The two top vents sound like maybe five square feet or thereabl0uts, I don't know the diameter of the base. There is a claim that they exhaust more than the sq footage allows because of fan action, but I don't believe too much of that. They move around in circles because of heat exhaust naturally moving up through them, but the claim is that the movement causes the air to exhaust.
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Thanks everyone for your replies. I don't have a warm and fuzzy concerning the construction practices of F&J. They were known more for what they didn't put in their homes as well as how ingenious they were at cutting corners than their quality of construction. I had additional insulation installed several years back. I asked them to verify the soffit vents were unobstructed and to be sure to not cover the vents. That being said, I'm not sure whether they did or not. With the deductible so high I'm just trying to get my roof done and maybe a little additional venting if it all feasible. My concern was the additional vents would cause a problem or wouldn't do anything other than cost me more.I don't think I'll be asking to have any additional vents be installed. However, I will ask to see how much additional cost for a vent-a-ridge.Thanks again for all the feedback.
I would either add a few more of what you have, or I would delete what you have and change to ridge vents.Do you have a hipp roof? That is a concern too. They are harder to balance venting at ridge and soffit.Ridge venting is best when balanced and in a new home, but can be trouble when mixed with other venting you already have.
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I thank the Good Lord I don't have a hip roof. My home is an L with 1 whirlybird on the north side and 1 on the west facing side.I will try to get an estimate to have the existing vents canceled and the ridge vent system installed. I may just have to settle for the old system. I've been in the house over 20 years and don't think the old system has been too hard on the house. Thanks
my 2 cents worth, anything with moving parts needs maintenance, when out of balance turbines squeak and drive the hood crazy .. I prefer the chimney type vents, just as effective and no moving parts .. now about the cts ridge vents .. they are great but a driving rain blown up the roof can get under them .. that said I did a fpl chimney install last year, stick your head in the rafter bay with the vent hole in it, very cool, in the rafter bay beside it, very hot .. soffits were completely vented .. I think cts ridge is the way to go if you can keep the water out, and if your not in a deep snow area ..
No snow in Dallas ....We do have bad rain storms. This is the reason for the new roof (Hail Damage). The hail tore up the shingles, gutters, patio cover, car port cover, took out one whirlybird, a couple of Vent tops plus my sons car.The insurance companies are crying big time as they had to replace nearly every roof in the neighborhood.I'll be speaking with the roofer this week and ask about the roof vent system.Thanks
I just jumped this hoop last fall.
First, what type of insulation you got up there in the attic?
Second, Piffin's numbers are correct for when only soffit vents are used. Add ridgevents or mushrooms up high and that number can be doubled, meaning fewer vents.
Third, IF you have cells now in the attic, some of them or other debris could cover the screen of the soffit vent, thus reducing it's efficiency. Blow them out with compressed air from outside.
Third, Mike Smith's "additional cells" gets you to the best and cheepest solution. As long as your exisiting vapor barrier is adequate.
Fourth, what type of new roofing are you getting? Here in Denver, the insurance companies pay out more in hail damage than anything else. Anything Else. My concrete tile roof has held up pretty good during some of those storms.
PeteI've rock wool and blown cellulose. As for a vapor barrier, there is none. F&J didn't think the home owner would need a vapor barrier.I've made an attempt to verify that air is getting into the attic from the soffits. However, there is really now way to tell is all of them are operational. The access to the attic is very limited and access to some of the soffits would require a long ladder or staging as they are up almost two stories.I had vinyl siding installed several years ago and they were suppose to verify the soffit vents were operational and then they were replacing them with their version of vinyl vents.My roof structure would not support a cement roof. I have roof 2x4 roof trusses on 24" centers with 3/8 sheathing. A small person is lucky they don't fall through the roof deck when on the roof. The insurance adjusted recommended that I have some additional decking installed on my dime. Thanks for the input.
Edited 6/3/2008 2:49 pm ET by timby
"My roof structure would support a cement roof. I have roof 2x4 roof trusses on 24" centers with 3/8 sheathing."
I assume you meant that your roof structure would NOT support a cement roof. Plywood aside, the roof trusses may not be designed for the added dead load.
A politician is a man who stands for what he thinks the voters will fall for.
Unfortunately, siding guys are well known for covering up vents when they put up their "ventilated" soffit. If the perforated area of the soffit doesn't mate up with the hole in the plywood soffit then you're hosed. And even under the best of circumstances the vent holes are smaller than the previous vent, effectively downsizing the opening.
It is an ironic habit of human beings to run faster when we have lost our way. --Rollo May
DanI have to agree there seems to be a big difference between the old screen soffit vents and the newer vinyl ones. However, not much to be done other than to take a drill to them and hope not to do too much damage.
The installers should have cut the openings wider before installing the new soffit, but few do.
It is an ironic habit of human beings to run faster when we have lost our way. --Rollo May
DanI was told that they removed the wire screen before installing the new vinyl soffit vents. I seriously doubt that was done. However, I'm not sure. I would have to pull out the section and look. That would be a horrid undertaking. I may have the roof guys try and look. We'll see.
Lots of folks (validly) question the efficacy of turbine vents. And they're ugly as sin.
While many suggestions so far have been valid, they have all glossed over one point: air flow.
That is, you can take out only the air that goes in. If you have more vents taking air out, you need more vents bringing air in.
The other aspect is that you don't always want a lot of air flowing through the attic. For example, in winter, you want to use some of the heat your attic can trap.
A ridge vent has the advantage of encouraging smooth flow over the entire underside of the roof.
A turbine has the advantages of not requiring power, being easy to add to a roof, and being easy to cover in the winter.
Temperature sensitive attic fans only work when it's hot ... but you need power for them.
However you do it, make sure to add more ways for air to enter the attic - preferably so that it travels along as much of the underside of the roof as possible on the way out.
" they have all glossed over one point: air flow.That is, you can take out only the air that goes in. "Methinks the glossing over was in your reading skills.
Most of the exchanges in this thread have been discussing that very thing and how to calculate it.Not a thing wrong with what you said, but try not to discount the fact that it was already written
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True, but most of the discussions were focused on square inched of vent to remove hot air; buried in the numbers was but an indirect mention of the need to let air in. Perhaps it's just a quirk of mine, but I've seen far too many examples, where someone insists they need a bigger, faster, more powerful exhaust fan - yet, when I arrive, I hear the old fan going 'whomp whomp' - a telltale sound of a fan that's starved for supply air. As you might guess, often it's the addition of ever more insulation that results in blocking the flow of fresh air into the attic. All those square inches are useless with a pile of "snow" blown behind them. Nor does the simple math address airflow. If the fresh air comes in near the exhaust - and don't forget the channeling effect rafters can have - that air flow will remove very little heat from an attic. Want to really get minimal results from maximum effort? Combine a ridge vent with gable vents on either end. Sorry if you took my comment personally; it was not meant that way. I am sure you have personally seen many ineffective venting schemes. Even the best equipment and finest craftsmanship cannot overcome a poor design.
In a perfect world the builder would have taken all these things into mind when building the home. Instead the home owner hopes that the minimum effort was afforded when the venting was installed.That being said, F&J was only interested in the bottom line and didn't care about down the road. When I first moved into the home, over twenty years ago, I asked the house inspector why there was only 3 inches of insulation in the attic. He told me "Son, we don't worry about heating the home only cooling". SO there you go. I had additional insulation added cause I figured it would help in the heating and cooling seasons. I'm sure there was a certain amount of venting in the attic or I would have a serious mold problem. I forgot to mention that I don't cover my whirlybirds in the winter as then I would be in serious trouble. My furnace takes it's combustion air from the attic, also all the bathroom vents vent into the attic (another common occurrence in this area).I was trying to figure what balance of air flow was needed for my home. Also, what was the most effective way to vent the attic.Thanks for your input. I like to take advantage of this sites expertise when ever possible.
Update on my new roof and decisions on venting .....
I went with the Vent-a-ridge solution instead of adding new Wind Turbines. I can already tell a big difference in the house. We've been experiencing a big heat wave (100 + every day) and have noticed it doesn't take as long for the house to cool. The temps and humidity seem better in the home.
I wish I would had this done the last time I had my roof replaced.