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01-21-2011, 11:59 AM   #16
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Quote:
 Originally Posted by jmiller 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.

The attached image is the suggested (50/50 NFA @ 150) ventilation for my attic space. So this would work. But more is better if available, right? What if I wanted to maximize my full soffit intake area... i.e., run it the full 37' on each side of the house instead of just the 26'. So, instead of 52' of intake I go 72' (almost the entire length). That would of course up the ridge vent length too. Again I have approx. 37' of ridge to work with. So a 30' ridge vent seems to work well...?

Also I figure if I go with the 60/40 vs 50/50...

72' (INTAKE) x 9" NFA = 648" NFA
30' (EXHAUST) x 18" NFA = 540" NFA

648" NFA (approx. 60% soffit)
+ 540" NFA (approx. 40% ridge)
________
= 1188" NFA

That's 9 total pieces of Continuous Soffit Intake Vents - 9 sq.in./foot NFA
(4.5 each side) - OR - 648" NFA / 9 sq.in./foot NFA = 72' / 8' pieces = 9 total vents

I THINK
Attached Thumbnails

 01-21-2011, 12:01 PM #17 Member   Join Date: Dec 2008 Location: NW Chicago burbs Posts: 383 Rewards Points: 250 There are many many threads on attic ventilation. Based on pro commentsit sounds like it is very common for roofers and estimators to not be knowledgeable about ventilation.
 01-21-2011, 01:40 PM #18 Registered User   Join Date: Mar 2009 Posts: 11,730 Rewards Points: 526 NS, you need to have soffit vents across every rafter bay to move the heated air with moisture from the rooms below. Otherwise there will be dead air spots that will get condensation on the roof, framing or insulation. The 150/300 rule is an older one, if you ventilate on a 1/100, you are still fine. Working backward; 37 x 9 int. = 333 / 144" = 2.31 x 2 sides = 4.63 total int. + 4.63 exh. = 9.26 total 37 x 18 exh. = 666 / 144" = 4.625 exh. Gary __________________ If any ads are present below my answer or words underlined/colored, I do not condone/support/use the product or services listed/linked to, they are there without my consent. 17,000 dryer fires a year, when did you last clean the inside of the dryer near motor or the exhaust ducting?
 The Following User Says Thank You to Gary in WA For This Useful Post: nickelshine (01-21-2011)

05-29-2012, 09:12 AM   #19
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## Resolution?

Over the weekend I discovered that our house, built in 1986 and just purchased the week before, has exactly the same problem that nickelshine described: vinyl siding covering solid wood soffit, so no ventilation.

I'm curious to know: did you solve your problem?

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