Installation Details · FAQ

How do I calculate the ventilation my attic needs?

Use the 1:300 rule from the IRC: divide your attic floor area in square feet by 300 to get the total net free vent area required in square feet. Split that 50/50 between intake (soffit vents) and exhaust (ridge or gable vents).

For a 1,500 square foot attic in Madison County: 1,500 ÷ 300 = 5 sq ft total = 2.5 sq ft each of intake and exhaust. Most ridge vent products spec 12 to 18 square inches of net free area per linear foot, so 2.5 sq ft ÷ 14 in² per ft = roughly 26 linear feet of ridge vent. Trill measures your attic at the inspection visit and quotes the exact ridge length needed alongside the shingle estimate.