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-   -   Vinyl Perf Soffit over Wood - No Vents (http://www.diychatroom.com/f9/vinyl-perf-soffit-over-wood-no-vents-92011/)

nickelshine 01-11-2011 04:16 PM

Vinyl Perf Soffit over Wood - No Vents
 
What do you think is the best idea for installing soffit vents with the below scenario...

Our PA house (bought 4 years ago) has vinyl siding with perforated soffits, but the no actual holes for ventilation in the wood soffit underneath. The house is 37' wide (attic total 962 sq ft) with about 14 perforated vinyl soffit pieces on each side, measuring approx. 4" x 8" each. I intend to put in a ridge vent measuring 34'.

From the attic ventilation calculator, I believe the 28 existing 4" x 8" perf vents would be about 60% for intake if they had an opening in the wood frame. Though small perf holes may not live up to that figure...

The Question...
How would you handle installing soffit vents? Remove the entire soffit board and reinstall only the existing vinyl perf soffit, possibly weakening the structure of the roof?? Remove vinyl temporarily and cut 4" x 8" holes thru the existing wood soffit to align with the existing vinyl perf soffit area?? (no idea if they align w/rafters) Or, remove the vinyl altogether and install either single or continuous soffit vents in wood? (wood maintenance issue)

Thanks.:thumbup:

Roofmaster417 01-11-2011 09:41 PM

I have never been a fan of vinyl anything but siding, If you can afford it go with continuous. :)

Gary in WA 01-12-2011 08:13 PM

I agree with RFN, above. But if you have to use vinyl...... The perf sections are only +-4.5 sq,in. per ft., so the soffit would need to be 24" deep from the fascia to house to get the required 9 NFVA per ft. to match 1/2 the ( baffled hopefully) ridge vent (18 NFVA) for each side of the roof. http://files.buildsite.com/dbderived...rived92755.pdf

http://www.oikos.com/esb/30/atticvent.html

I would pull wood soffit boards at the fascia to accept the continuous strip vent, add blocking for the vinyl "J" channels and cut the old to fit, Fig.s 63-71; http://www.vinylsiding.org/publicati...2007Manual.pdf

The con. vent needs to be next to the fascia to get optimum air pressure, not close to the house, page 616; http://books.google.com/books?id=Z8a...0vents&f=false

No fear on weakening the roof, soffits are usually non-structural. Your figure sound off..... Compare to this; http://www.airvent.com/homeowner/pro...it-specs.shtml

Gary

nickelshine 01-13-2011 08:31 AM

Thanks Gary, great information. My soffit is small, maybe a 6" width, so it sounds like the continuous vent is the way to go. While I was thinking to reuse the existing perforated vinyl if possible, you certainly made clear the more important requirements.

Roofmaster417 01-14-2011 06:25 PM

Well GBR in WA,I have to admit thats some impressive stuff.:thumbsup::thumbsup::thumbsup::thumbup:

Gary in WA 01-14-2011 07:36 PM

RM, thank you. Feel free to use them when-ever.

Nickelshine, glad we could help! Any other questions, there are a lot of roofers on this forum that can help, just ask away.....

Gary

Roofmaster417 01-14-2011 08:45 PM

Thanks GBR in WA....,but I am starting to build my album under my profile, check it out. :)

beerdog 01-16-2011 11:11 AM

Gary...do you have a picture of a combination soffit and continuous vent installation. I have ot do this same project on a 1foot soffit overhang. My overhang has vented soffit over the original plywood soffit. Someholes are drilled in the wood but I know it is not enough.

Gary in WA 01-16-2011 01:39 PM

Sorry, no pictures. Just add framing dropped off the rafter/wall to the elevation you need. Install a 2x running with the cont. vent, next to, for a soffit nailer as well; http://books.google.com/books?id=E5S...raming&f=false

Gary

nickelshine 01-19-2011 09:25 AM

Spoke with my first roofer about an estimate for ridge vent, continuous soffits vents and two bathroom exhaust vents. Well, he never heard of continuous soffits vents. I tried to explain the concept. Even fired up the internet and showed him the product. He said that he was not interested in learning to install the vents on the job, and decline to estimate my work.

Is this a east coast/PA venting ignorance that I should expect from others?:huh:

nickelshine 01-20-2011 04:18 PM

Quote:

Originally Posted by nickelshine (Post 573673)
Spoke with my first roofer about an estimate for ridge vent, continuous soffits vents and two bathroom exhaust vents. Well, he never heard of continuous soffits vents. I tried to explain the concept. Even fired up the internet and showed him the product. He said that he was not interested in learning to install the vents on the job, and decline to estimate my work.

Is this a east coast/PA venting ignorance that I should expect from others?:huh:

Second roofer was more open to the continuous soffit install, but also suggested the option to install perforated vinyl the entire length instead. He seemed to feel that would be even better than the say an Airvent continuous soffit. I believe from the responses above this may be incorrect, and the continuous would still beat the entire length in perforated vinyl...

- Soon to install a 34' ridge vent @ 18" NFA = 612" or 4.25' NFA for ridge.
- Soffit width (one side) = 37' x 6" - With 37' of C-soffit @ 9" NFA per ft = 4.625" total, after including both sides of the house. Seems slightly better than 50% intake :thumbup:

- Perf vinyl @ 4.5" NFA per ft, so total vinyl would only be like 333" or 2.3' NFA intake - not enough intake even with the full length of perfed vinyl...

Have I passed? :eek:

Gary in WA 01-20-2011 06:20 PM

Yep! "The perf sections are only +-4.5 sq,in. per ft., so the soffit would need to be 24" deep from the fascia to house to get the required 9 NFVA per ft." From post #3. You always want equal or slightly more intake than exhaust or the negative pressure will pull gas flames, house conditioned air, etc. first, rather than soffit air.

Gary

jmiller 01-20-2011 07:00 PM

Quote:

Originally Posted by nickelshine (Post 574548)

Have I passed? :eek:

Did you calculate the needed ventilation for an attic your size? The ridge vent may not need to be continuous to get the minimum exhaust, which solves the problem of lack of room for intake if you can leave some uncut. It's better to have more intake than exhaust, than it is to have 'continuous' ridge vent, so long as you satisfy codes.

beerdog 01-21-2011 10:08 AM

Isn't the intake volume supposed to be equal to or greater than the exhaust? Sounds like the contractors are recomending what is best for them, not you. My experience so far when dealing with roofers is that the only ones who understand ventilation are the ones on these discussion boards.

nickelshine 01-21-2011 11:48 AM

Quote:

Originally Posted by beerdog (Post 574981)
Isn't the intake volume supposed to be equal to or greater than the exhaust? Sounds like the contractors are recomending what is best for them, not you. My experience so far when dealing with roofers is that the only ones who understand ventilation are the ones on these discussion boards.


Yes, after only two estimate visits and trying to explain what I want, I feel like I am being a difficult customer. Maybe a "Ventilation Snob" even ... Just trying to educate myself on the site; figured they would already be aware of this info.


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