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Proper venting combination questions...


George Sharrett
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Greetings,

An engineer in town just called me with an interesting question. "Do you have any written documentation to show that gable end vents and continuous ridge vents should not be used on the same roof?"

I had to admit that I had never herd anything about this but that the idea of the gable vents some how "short circuiting" the upward flow (convection) from the soffits to the ridge was interesting. The idea is that the gable vents would feed the ridge vents and there would be little or no air movement through the main area if the attic.

This seems very unlikely to me in the real world but hay, I have been wrong before and surly will be again in the future...

Are there any roofing experts out there with documentation about this?

Many thanks,

George

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It has also been my understanding that gable louvers should never be used with ridge ventilation. Having "balanced" attic ventilation is the goal. Check out the following link.

http://www.inspect-ny.com/interiors/atticcond9.htm

Although I have to say that I have seen many homes with both ridge and gable vents that had no moisture build up, yet others configured that way with serious ventilation problems/damage.

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http://www.guardianbp.com/docs%5Cguardv ... struct.pdf

CALCULATING THE PROPER VENTILATION NEEDS

For the ventilation system to function properly, the ridge vent must be the only exhaust vent for the vented attic space. Do not use

with roof vents, pot vents, power vents, turbine vents, or gable end louvers. The intake and exhaust ventilation should be balanced.

Manufacturers installation instructions.

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Hi George,

Yes, it's absolutely true. About 14 - 15 years ago, when Certainteed still owned Air Vent Inc., Certainteed commissioned a university study (University of Illinois, I think) of attic ventilation principles and published the results of that study in a booklet entitled Principles of Attic Ventilation.

ONE TEAM - ONE FIGHT!!!

Mike

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Greetings,

An engineer in town just called me with an interesting question. "Do you have any written documentation to show that gable end vents and continuous ridge vents should not be used on the same roof?"

I had to admit that I had never herd anything about this but that the idea of the gable vents some how "short circuiting" the upward flow (convection) from the soffits to the ridge was interesting. The idea is that the gable vents would feed the ridge vents and there would be little or no air movement through the main area if the attic.

This seems very unlikely to me in the real world but hay, I have been wrong before and surly will be again in the future...

Are there any roofing experts out there with documentation about this?

Many thanks,

George

Check out the CertainTeed Shingle Applicators Manual under the Chapter titled Ventilation. The other major manufacturers (Owens Corning, Tamko, GAF) strongly recommend this but only CertainTeed (to my knowledge) requires it for the warranty to be in force.

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I am currently in the process ($$$) of replacing my roof, to include new sheathing (split / shingle / comp overlay). To add insult to injury, I have ONLY gable venting which up to this point has worked extremely well - absolutely no visible moisture problems in the attic and the comp has been on for 21 years. From all I have read I need to #1) close off the gable vents, 2) install a full ridge (which I had planned on doing), 3) cut out the solid soffit bird blocks and install screens - now this is a royal pain in the backside no matter how one approaches it. Being 65 I don't look forward to hanging off a ladder for 2 days. I recall recently seeing what appeared to be a horizontal full "soffit" vent installed on the lower portion of the roof but can't quite remember where I saw it (duh) and didn't take a picture of it. Has anyone ever seen this setup or was it a "roofer modification"? I guess one could cut a ridge section in half, groove the sheathing and install it with adequate protection from wind / rain - any thoughts?? E-mail me at "oregonwest@comcast.net" if you feel to. Thanks

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Uhm, why are you replacing a fully functional ventilation system? Are you sure the soffit/ridge system will function at least as well? The shingle warranty should not be dependant on your vent configuration for an existing structure, if it is you need to select a different shingle.

I have modified at least three roof vent systems this year where the soffit/ridge vents were not working and additional ventilation was needed.

Tom

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Paul,

That's an Air Vent product. I've seen it installed in a new home and saw it at one of Air Vent's presentations. It's not drip edge, it's installed on the top (covering side) of the roof about 1-2 feet up from the edge and beyond the eave/sofit area. It works like ridge vent except it's an intake.

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Hi Paul,

Is this the full-length soffit vent material you're talking about? If you don't want to have to stand on a ladder craning up to cut that strip out of the soffits, consider the vented drip edge option that Brandon posted above.

Besides the vented drip edge at the link that Brandon gave you, Certainteed also makes an Edge Vent that's kind of like a ridge vent cut in half. This is designed for houses with little or no eave overhang, though.

By the way, you can download the installation instructions in pdf format for any of those from the Certainteed site.

ONE TEAM - ONE FIGHT!!!

Mike

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I think the lowest edge of the vent was 12 inches or so (maybe a little more) up from the drip edge. The ventilation needs to be up the roof far enough so that the air enters the attic space not the eave area.

I also believe that at an Air Vent seminar/presentation the presenter told us straight up that it could be installed in such a way. I did read the install instructions, looks like they say it should only be installed at the edge.

Seems to me that it shouldn't matter so long as the intake slot that is cut in the sheathing is as low as possible in the attic space. So if there is a little overhang having the edge vent up the roof a bit should not be a big problem.

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