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Old 10-26-2013, 01:21 PM   #1
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Attic vent computations

I'm in a house that was built/evolved in the 1920's-30's-40's and 50's. Construction methods used have been interesting, to say the least, in various parts of the place.
The latest is that it needs a new roof. I have been concerned about attic ventilation since I've been here, there are only two 6" square vents at the two peaks, one at each peak. The house plots out to about 1600 sq. ft. It is a one story house so I thought I could equate attic floor space, which all the ventilation guidelines seem to be based on, to the living space of the house. All of the ventilation guideline charts indicate 1 sq. ft. of ventilation for 150 sq. ft. of attic floor space which comes to 11.6 sq. ft. of ventilation, half that if an equal amount of soffit vents are employed.
The supplies for the new roof showed up the other day and the contractor sent 4 - 9.25" diameter roof vents, which total about 2 square feet. My question is whether there is some way that attic volume is factored in? Like I said, this place evolved over several decades and, as a result, there are a couple of different roof pitches, from 7:12 to 3:12. If I subtract the area that has less than a 7:12 pitch from the 1600, the contractor would be close provided adequate soffit venting was provided.
Is this sound reasoning or do I need to get the contractor to add more vents? The supplies are here but the crews won't be here till Wednesday so I got a couple of days to get this sorted out.


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Old 10-26-2013, 02:38 PM   #2
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Please post a picture of the house.
You can never have to much roof venting.
I just do not have the time or patience to do all the math.
I just add a ridge vent and vent all the soffits.
A few round vents are better then nothing but only vent a circle and there's still hot moist air going to be trapped in the rafter bays.


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Last edited by joecaption; 10-27-2013 at 12:29 AM.
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Old 10-26-2013, 04:06 PM   #3
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Based on attic floor space, not volume;

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