Soffit and Fascia Calculator

Soffit vents are the intake half of attic ventilation. The IRC asks for 1 square foot of net free vent area per 150 square feet of attic floor, relaxed to 1:300 when the venting is balanced high and low and a vapor retarder is present — and roughly half of that area belongs at the soffit, half at the ridge. Vented vinyl panel supplies only about 5–10 in² of net free area per linear foot, so read the manufacturer’s NFA rating instead of assuming a perforated panel is enough. Solid panel belongs only where there is no attic above, such as a porch ceiling. Treat this as a planning estimate; your local code official governs.

Vinyl soffit is cheapest at roughly $2–$5 per square foot installed, never rots, and comes vented or solid — but it can sag on wide overhangs without a center support and yellows in strong sun. Aluminum runs about $4–$8, spans better, and is what most gutter contractors stock because they can brake matching fascia wrap from the same coil. Fiber cement is $6–$12, paintable, and the right match on a historic house, though it is heavy, needs finishing, and cutting it releases crystalline silica — use a dust-collecting blade and respiratory protection.

Rot, almost every time. Fascia sits directly behind the gutter, so once a gutter overflows, backs up with ice, or the roof is missing drip edge, water wicks into the top edge of the board and stays there. Probe suspect boards with a screwdriver — anything the tip sinks into more than about 1/4 inch is gone. Replace the wood itself rather than capping it: wrapping rotten fascia in aluminum coil hides the damage, traps moisture, and leaves the gutter screws nothing solid to bite. Check the rafter tails behind the board while it is open.

Yes, and the sequence matters — fascia goes on first, then the gutter hangs off it. Hanging new gutter over old fascia means paying twice when the board eventually fails, plus the cost of taking the new gutter back down. Contractors routinely bundle the two, which saves a set-up and a round of staging or ladder work and commonly trims 15–25% versus separate visits. The same logic applies to a reroof: drip edge, ice-and-water shield, and the fascia detail all meet at that edge, so schedule them together if a new roof is near.

Soffit area is just the eave run times the overhang depth, so 140 ft of eave with an 18-inch (1.5 ft) overhang is 210 square feet. Vinyl and aluminum soffit panels are typically 12 ft long by 12 in wide, covering 12 square feet each — that is 18 panels of field coverage and 20 once you add the standard 10% for corner returns and end cuts. Measure the overhang from the wall sheathing to the inside face of the fascia board, not out to the shingle edge, since the drip edge projects past the fascia by another inch or so.