Calculating NFA for metal roof attic
What amount of venting would you recommend for this attic/roof system?
Presently unvented. Tar paper and 1020’s asbestos shingles with redwood gutters painted with lead based paint.
New roof: standing seam metal with solar.
In a high fire zone.
1500 square foot insulated attic, 6:12 pitch, or about 1600 square feet of actual roof material.
Current venting: none.
Mechanical in attic: none
Climate zone: 3C
Quake Distance: 101 meters to major fault main trace, outside Alquist Priolo Special Studies Zone.
Width of overhangs about 4 inches all around.
Length of new metal ridge: 19 feet, NFA of available ridge vents appears by be 17 in/sq NFA per lineal foot.
Using “1 square foot of vent per 150 square feet of attic” I get a NFA of 720 square inches total (divided by 2 for eave and ridge). Using GAF’s online calculator for shingles gives 360 square inches, so same number.
(IRC), Section R806 seems to be exactly half that.
Your thoughts energy nerds?
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