Attic Ventilation Balance

Attic ventilation is one of the most over-promised and under-delivered parts of residential roofing. Many homes have a ridge vent installed — but no working intake at the soffit, so the ridge vent is just a hole that doesn't move any air. The result: superheated attic in summer (which fries shingles from below) and ice dams in winter (which cause water damage). The technical requirement (per IRC code): - Total ventilation area = 1/150 of attic floor area (or 1/300 if vapor barrier is present and intake/exhaust are balanced) - Split roughly 50% intake (soffit vents) and 50% exhaust (ridge, gable, or powered vents) - Net free area (NFA) is the metric that matters, not square footage of vent product (most vent products are 30-60% blocked by mesh) Common failures: - Ridge vent installed over solid decking (no slot cut) — common shortcut that produces zero airflow - Soffit vents covered by insulation that's been blown into the attic over time - Mixing ridge vents with gable-end vents (they short-circuit each other) - Powered attic fans installed without adequate intake (the fan pulls conditioned air from the living space below) Every roof replacement is an opportunity to fix this. A competent installer inspects soffit ventilation, calculates NFA balance, and either installs proper ridge slot + new soffit baffles or recommends an alternative (gable vents, mechanical ventilation) that actually moves air. Skipping this conversation is malpractice. For estimating: ventilation upgrade is a per-job add-on that pays back fast. $200-$500 in labor and material can extend shingle life by 3-5 years and prevent thousands in ice-dam water damage. Always quote it; most homeowners say yes once they understand the math.