DIY Home Improvement, Remodeling & Repair Forum > DIY Home Improvement > Roofing and Siding > Cathedral ceiling - how much venting do I need?




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Old 10-23-2012, 06:56 AM  
Shawner
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Quote:
Originally Posted by AndyGump View Post
This is what he stated.

Should reverse those percentages.

Andy.
The link stated the following: "Calculate the intake and exhaust venting percentage based on 60% intake vents (soffits and eaves) to 40% exhaust vents (near the roof ridge). You could make simpler calculation of 50/50, but most experts recommend a 60/40 split."

That's incorrect?


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Old 10-23-2012, 08:46 AM  
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I think if you dig into the science of venting and calculating and percentages, you would find that it's all about a regular attic space and how you want to move the air thru the attic. Keep in mind that a shed roof has a very limited air flow path in cubic inches. It also has two heat sorces in the winter so I think your best is just to figure as much as possible in and out.



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Old 10-23-2012, 06:19 PM  
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Originally Posted by oldog/newtrick View Post
First thing to check is the ability to free flow air from the eave to the peak, because if it's stuffed with insulation all the venting in the world will not help.
Opened it up on the intake side and saw this:


Great! They cut ventilation in when they did the soffits, guess I was worrying for nothing!!


Then I cut it out further so I could stick my head in:


Pulled that piece of insulation down and it looks like it's insulated to the sheeting, I assume over the length of the roof.

Olddog, like a prophet.

Not planning on doing anything about it until I re-roof (roof has been on for 10 years or so, no major issues as far as I can tell). What can I do? Pull off the sheeting, shim it and re-sheet?
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Old 10-23-2012, 07:38 PM  
oldognewtrick
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You can put a vented ISO board over the top of the existing when you re-roof. It consists of a ISO board, an air space and decking on top.

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Old 10-23-2012, 07:49 PM  
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By your last picture it would appear that the rafters are 2x6s I suspect that they are 2x10s and the bottom has a flat section sitting on the wall and the section in the eaves have been cut down to 2x6 just for the look. I think if you could reach further in you would find some space between the insulation and sheeting and you might find that air shoots were installed in every other or every third bay.
It doesn't make sense that the same people who put down new insulation and sheeting and then took time to cut holes in old soffet if they new air could not get thru.



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