Roof Vents

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Old 04-21-05, 06:11 AM
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Roof Vents

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I have about 1700 sq ft of attic space (based on 2nd floor sq footage). How many roof vents should I have? I had an air handler installed in the attic and it wasn't cooling properly. The HVAC guy said my attic was getting too hot and needed more ventilation. There are currently 5 vents plus multiple soffit vents. Any thoughts or opinions?
( I originally posted this in the "Roofing and Waterproofing" forum but thought this was a better place to ask the questions.)
 
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Old 04-21-05, 07:31 AM
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Wink

Should have about 1 sq ft vent for every 150sq ft attic.
1/2 in and 1/2 out. Attic power vent fan on a tstat is good also attic sq ft X0.7== CFM of fan.

ED
 
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Old 04-22-05, 02:28 PM
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Newsy,

You can reduce the formula by Ed to 1 sf per every 300 sf if you do at least half high. The theory is that if you have frieze blocks or soffit strip vents at the lower part of the roof and you then provide either gable end or low profile vents your roof will then convection out the hot air naturally. So in your case it would be 1700/300=5.67 sf. if you use frieze blocks with (3) 2" dia holes you have .10 sf per block. 1/2 of 5.67 is 2.83 sf frieze venting is 29 blocks. Then you would place either a couple of gable end vents or 8 low profile vents spaced on both sides of the ridge a few feet down.

I hope this helps.

Brian Garrison
General Contractor/Professional Building Designer
 
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Old 04-23-05, 09:03 PM
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Thank you guys for the response. I have a hipped roof so gable vents aren't an option. I'll probably look into a powered vent with a thermostat. My attic reached 133 degrees on a 90 degree day last summer... I need to do something pretty soon.
 
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Old 04-24-05, 04:31 AM
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You say hip roof here .I have lots of time run the ridge board on out over the hip roof and made it into a small gable there. If need be for air up there.

ED
 
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Old 05-15-05, 03:30 PM
mattpole
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Originally Posted by Newsy
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I have about 1700 sq ft of attic space (based on 2nd floor sq footage). How many roof vents should I have? I had an air handler installed in the attic and it wasn't cooling properly. The HVAC guy said my attic was getting too hot and needed more ventilation. There are currently 5 vents plus multiple soffit vents. Any thoughts or opinions?
( I originally posted this in the "Roofing and Waterproofing" forum but thought this was a better place to ask the questions.)
 
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