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Example of how to calculate net free area:
1200 square foot attic divided by 150 square feet = 8 square feet (1200 / 150 = 8)
8 square feet times 144 square inches = 1152 square inches (8 x 144 = 1152)
1152 square inches divided by 2 = 576 square inches at soffit and at exhaust (1152 / 2 = 576)
Asphalt shingles refers to the field shingles used on the faces or facets of the roof. Asphalt shingles are not to be used in the hips and ridges of the roof.