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10-22-2012, 04:09 PM   #1
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## Cathedral Ceiling - How much venting do I need?

Guys, meet my roof. Well, part of it anyways. The raised part is the cathedral section.

Here's the exhaust side of the venting. Aluminum soffits are covering up cedar with holes drilled into it. Haven't pulled them down yet to see exactly how much there is.

Found a site about calculating proper attic ventilation (http://www.trinityexteriorsinc.com/1...n-5-easy-steps), wondering if you could check my calcs below and see if I'm correct.

Area = 25' x 23' = 575 sq ft

TFNVA = 575 sq ft / 150 = 3.83 sq ft

Convert to inches = 3.83 sq ft * 144 = 552 sq in

Intake = 60% = 331 sq in
Exhaust = 40% = 221 sq in

So if I pull down the soffits, count the number of joist bays I have, figure out the size of hole I need to cut in each to total 331 sq in on the intake side, I should be good, right? If that's ok, should I staple in some screen material over the holes to keep the critters out or do the soffits do that already?

I'm not positive but I don't think I have to worry about baffles (don't think the insulation is up that high in the "attic")

Thanks for any help!

Last edited by burnt03; 10-22-2012 at 04:11 PM.

10-22-2012, 07:39 PM   #2
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Any reason you are concerned? There would have to be 12 1" holes per foot in order to have adequate ventilation. I'm going to guess that isn't the case. If you cut a 1" wide slot the entire length you should meet your vent area.

 10-22-2012, 08:03 PM #3 Member   Join Date: Sep 2009 Location: BC, Canada Posts: 250 Rewards Points: 152 I had pulled a piece of soffit down on the exhaust side to check out where a bat had been living and noticed that there looked to be 1 - 1 1/2" hole every foot or so, so like you say, nowhere near the amount of venting needed. Cutting a strip out is a way better idea than a bunch of random holes, thanks

 10-22-2012, 08:12 PM #4 Member     Join Date: Dec 2003 Location: Chicago Posts: 614 Rewards Points: 552 Ditch the soffit vent. Look into the Air Vent, Inc. Peak Filter Vent. I commonly use it on projects like yours. It is continuous so will give you maximum exhaust. You should also look into some intake. __________________ -Grumpy http://www.illinoisroofinspections.com The information found in this post is not to be considered legal advice. The author of this post takes no responsibility for any losses that occur. Use at your own risk.

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