08/20/2026
Ridge (exhaust) vents are continuous — sold and measured in linear feet, rated by NFA per foot.
Soffit (intake) vents are typically individual units (like 8×16 rectangular vents) or continuous soffit strip, each rated by NFA per unit or per foot depending on the product.
> Take your attic square footage and divide by 300 — that’s your total ventilation requirement in square feet. Convert to square inches (×144), then split it 50/50 between intake and exhaust. Ridge vent is continuous, so you’ll need enough linear footage to hit your exhaust NFA target. Soffit vents are individual units, so you’ll need enough of them (or enough continuous soffit strip) to hit your intake target. Check the product’s NFA rating — don’t assume a fixed spacing.