I am building a house with a truss roof 24″ on center, 2X6 top cord that sits on the outside of the top plate [no built up heal], and 2X6 freeze block. I want to vent through the freeze block [with two 13/4″ holes drilled in each block] and out the ridge. I can see two problems though. How to I get enough air through the freeze block holes and how do I insulate the roof without blocking the vent holes. Thanks for any and all comments.
Paul
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Greetings Stealman, Welcome to Breaktime.
This post, in response to your question, will bump the thread through the 'recent discussion' listing again.
Perhaps it will catch someones attention that can help you with advice.
bump
Spaghetti? The secret is in the sauce!
Hunts with garlic.
The roof shingle manufacturer may dictate how much attic ventilation is necessary, for them to honor thier warranty.
I believe it was in JLC that I pasted the following quote from.
"George Allaster of GAF’s Cobra Ventilation Division says that most shingle warranties require 1 square foot of ventilation for each 150 square feet of attic. If the roof has ridge and soffit vents, this is reduced to 1 Square Foot of ventilation per 300 square feet."
In other words, quanity and the size of the soffit vents is not arbitrary, it's deduced.
Each ridge vent manufacturer will declare a "clear venting" value per lin. foot for their product. For an attic 40'x60'= 2400 SqFt
Divided by 300= 8.00 SqFt of venting. If the ridge vent has a "clear vent" value of 7.2 SqInches per LF, then you have 1 SqFt per 20 feet of ridge; or 3 SqFt. Therefore, you need to have the total soffit vent area to be a sum total of 5 SqFt. Each soffit vent has a stamped value, as well.
There are styrofoam "chutes" that staple to the roof underside, that keep attic insulation away from the soffit vent's airstream path. They are something like 15 1/2"W x 3' or 4'L.
You also might look into specs on the "foil-faced" roof decking.