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fixit

06:36PM | 12/12/03
Member Since: 08/15/03
How many soffit vents I need for my attic?
Where can I find the R Values for NY state?

Length of attic = 52 ft
Width of attic = 22 ft
Height of attic = 6 ft

pgriz

10:42AM | 12/17/03
Member Since: 01/21/03
The ventilation rule I follow is to provide 1 sq.ft. of ventilation for every 150 sq.ft. of attic space. This needs to be balanced, so that 50% of ventilation forms the inlet at the soffits, and 50% forms the outlet at the vents. Perforated soffits have different degrees of penetration, some have as little as 0.01 sq.ft. of ventilation for every sq.ft. of soffit, and some have higher number up to 0.06 sq.ft.

Your attic is 52x22 = 1144 sq.ft. requiring 7.6 sq.ft. of ventilation (1144/150). 50% (or 3.8 sq.ft.) needs to come from the soffits. The perimeter around your house is roughly 150 ft. (52+52+22+22). Assuming that you have a soffit 1 ft. wide, you have about 150 sq.ft. of soffit. If you install ventilated soffits having clearance of about 0.03 sq. ft., you will have 4.5 sq.ft. (150 x .03) of effective ventilation, which is just a bit bigger than the 3.8 sq.ft. you need.

Is this what you were looking for?

Piffin

01:21PM | 12/27/03
Member Since: 11/06/02
None of the "experts" agree on this one, but I usually see recommendations of one foot for every 100 to 150 SF of living space. It should be ballanced so there is as much exiting the ridge vent as ther is coming in the soffits or it will be next to worthless, but not cut in half.

In other words, if you have a thousand feet of living space, I would put in ten SF of soffit vent and ten SF of ridge vent.

If you use typical 2" soffit on both sides and 4" ridge, you will exceeed that.

[This message has been edited by Piffin (edited December 27, 2003).]