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)
Hip and Ridge shingles are needed for architectural or designer shingles because the field shingles aren't designed or shaped to properly protect the hips and the ridges. Hip and Ridge Shingles are sized and shaped to protect hips and ridges.