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johnskat 07-24-2011 03:22 AM

Venting a Roof
 
Question on roof venting

Currently have a 1400 square foot house (1901) with gable vents and a functioning cupola. No soffit vents and no way of putting them in without lowering the ceilings in the entire house. We are replacing the shake roof with architechtural shingles next week and I am needing help with the following questions:

1. Will the gable vents be the intake when there is a functioning cupola (apx. 4 feet by 4 feet) to serve as the exhaust?

2. Should I close the cupola and gable vents and put in a ridge vent and roof vent (right above the eave)?

3. Should I forget about venting all together and install spray foam insulation on the roof deck and go with the unvented attic/conditioned attic?

The roof is very complicated design - has 7 gables total so there isn't a lot of room to put intake roof vents - if we installed a ridge vent on the entire house it would not be a 50/50 mix by any means.

Thanks in advance for your help. I really appreciate any help you can offer.



KJ; Portland, OR

josall 07-24-2011 08:25 AM

You might look at this;

http://www.airvent.com/professional/...-theedge.shtml

http://www.dciproducts.com/html/smartvent.htm#

johnskat 07-24-2011 10:40 AM

These are the products I was looking at for a ridge/lower roof vent. But I am wondering if this is my best choice? Purchasing these items will cost over $1,000 and will leave me with too much exhaust vents and not enough intake because of a very weird and complicated roof design.
Thanks for any help you can offer

Gary in WA 07-24-2011 03:52 PM

Built in 1901....... have you done any recent remodeling on it to warrant the additional venting? Is there a ventilation problem? Ice dams? Frosting/rusting nail points? Many houses along this Coast are fine with our moderate weather: http://www.fpl.fs.fed.us/documnts/pdf1999/tenwo99a.pdf

http://www.jlconline.com/cgi-local/v...170a32100a05c7

Gary

johnskat 07-24-2011 04:49 PM

We don't have any current problems with venting. We are concerned because we are removing the somewhat breathable shake roof and installing half inch plywood and asphalt shingles. Do you think that the gable vents and cupola are sufficient?

Gary in WA 07-25-2011 11:00 PM

Check with your local B.D. for minimum venting requirements.

Gary

josall 07-26-2011 06:15 AM

I did the exact same thing a couple years ago and your attic will be hotter. The FHA recommends a minimum of at least 1 square foot of attic ventilation (both intake and exhaust) for every 300 square feet of attic space, I tthink you wiill be better served witth something closer to 1 sq.ft. of vent for every 150 sq.ft.. of attiic space. It sounds to me like you need to get intake at the soffit level. For venting to work, cool air must come in the bottom, it heats up on its way up the roof and exists out the top. You can't suck air out the top if cooler air doesn't come in somewhere else. 1400 sq.ft. is 9.33 sqft of vent, so about 4.5 exhaust and 4.5 intake. If you use the air vent you would need 18 4' pcs. at $15 is $270.. each pc provides 36 NFA. If you cant get 18 on, anythhing you do is better.

Ed the Roofer 07-26-2011 11:23 PM

Quote:

Originally Posted by josall (Post 693770)
I did the exact same thing a couple years ago and your attic will be hotter. The FHA recommends a minimum of at least 1 square foot of attic ventilation (both intake and exhaust) for every 300 square feet of attic space, I tthink you wiill be better served witth something closer to 1 sq.ft. of vent for every 150 sq.ft.. of attiic space. It sounds to me like you need to get intake at the soffit level. For venting to work, cool air must come in the bottom, it heats up on its way up the roof and exists out the top. You can't suck air out the top if cooler air doesn't come in somewhere else. 1400 sq.ft. is 9.33 sqft of vent, so about 4.5 exhaust and 4.5 intake. If you use the air vent you would need 18 4' pcs. at $15 is $270.. each pc provides 36 NFA. If you cant get 18 on, anythhing you do is better.

Correction on your math.

Each lineal foot of the Shingle Vent II Ridge Vent provided 18 square inches of NFVA PER FOOT. So, each 4 foot section would provide 72 square inches of NFVA.

Otherwise, your recommendations for using the Smart Vent and the Shingle Vent II are right in alignment with my own preferences.

Ed

Ed the Roofer 07-26-2011 11:24 PM

Quote:

Originally Posted by josall (Post 692457)

I agree and enthusiastically endorse both of these products based on past job experiences going back many years with both product manufacturers.

Ed

josall 07-27-2011 06:56 AM

Ed, this was for edge vent not ridge vent.

Ed the Roofer 07-27-2011 09:43 PM

Quote:

Originally Posted by josall (Post 694568)
Ed, this was for edge vent not ridge vent.

Okay.

But, irregardless of my misquoting your combined links attempts, the Ridge Vent from www.AirVent.com called Shingle Vent II would still be a good recommendation.

Ed


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