Sufficient Ventilation

Old 09-20-02, 10:51 AM
abkent's Avatar
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Sufficient Ventilation

How much attic ventilation is adequate? I seem to remember there is a code based on the sqft of the attic space (1/150). When this is calculated is that total vent area (devided 50/50 top and bottom) or top area only?. My house is 2140 sqft + about 950 sqft over the garage. Most of the roof is 7/12 pitch with hipped ends of 9/12.

Also, what type of ventilation is preferred? Because my roof is hipped I worry about having adequate ventilation with ridge vents. What I plan to do is use turtle backs with soffit vents. Then place vents in the couple of gables that exist at one end of the house and use a attic fan to draw that air across to the other side of the house.

Any suggestions are welcome,

Old 09-21-02, 07:26 AM
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Lightbulb Don't mix

Use one type or the other, otherwise they will just "fight" each other.
The fan will draw air backwards through the roof vents etc.
The best solution is an all passive system, 1/150 ratio with 1/2 at top 1/2 at bottom.
Each "turtle back" vent is good for 50 sq in, you will need a lot of them
I personally like the turbine vents each one is good for 600 sq ft with proper soffit intakes, you will need 5.
5 turbines on a short ridge isn't the best looking thing on a new house.
With a large house/hip roof an attic fan might be the only alternative that looks good, it will be difficult to get 1/150 with a short ridge line.
If you must do the attic fan thing get one that uses a capacitor type motor, they will last longer than the 3-5 years of the standard type.
I have personally never seen one with a capacitor motor ever fail, but I'm sure they do eventually die.
Interestingly enough very few builders actually meet ventilation codes, even in todays new construction.
BUT the inspector passes it anyways and life goes on ....

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