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Frederic Urich 10-10-2011 09:10 AM

Single slope roof venting
How to calculate the amount of ehaust i need for a single sloped roof that is1/12, 36'x 38', 24" overhang with full vent soffit, low end proper vents to the high end which is 3' 2" above the ceiling insulation. Looking to put a verticle wall vent at the high end that is about 2" in height for the length of the 36' wall.

AGWhitehouse 10-10-2011 10:58 AM

A very nice venilation calculator:

Gary in WA 10-11-2011 11:00 PM

That calculator wouldn't go below 3/12 for your 1/12 slope for me. The other one for ceiling attics (as in your case) would, though, the other link.

You don't mention if it has a vapor barrier on the ceiling or not. If not, figure 9 square inches for every lineal foot of soffit intake and the same for ridge exhaust vents. This gives you 1/150, 1/2 total for 1/300.

Your 2" high sounds right, depends on the screening size, spacing of the wires for the NFVA- net free venting area:

Be sure you are getting 9 NFVA at the soffits, some manufacturers of punched vinyl de-rate it correctly;

I suggest 2-3" holes to maximize the intakes and exhaust because of the very low slope.


AGWhitehouse 10-12-2011 10:59 AM

2nd link has no data...

Gary in WA 10-13-2011 09:16 PM

End of second paragraph in your link, "NFA Calculator", from here:
OP, enter your square footage and lineal footage of soffit and ridge vent........


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