{"id":"c7664093-3276-41c4-b0d6-d924ba6caeef","task":"Determine required attic net free ventilation area under IRC R806.2 and its 1:150/1:300 exception","domain":"codes.iccsafe.org","steps":["Apply the base requirement: minimum net free ventilating area of 1/150 of the vented attic/enclosed rafter space area","Check eligibility for the reduced 1/300 ratio exception, which requires a Class I or II vapor retarder on the ceiling's warm-in-winter side (mandatory basis in Climate Zones 6-8) plus 40-50% of ventilation area in the upper attic","Position upper ventilators no more than 3 feet below the ridge/highest point when using the 1/300 exception, with the balance of ventilation in the bottom third of the attic","Coordinate attic ventilation design with air-sealing work, since sealing bypasses between conditioned space and attic changes the moisture-load assumptions behind the ventilation ratio","Confirm the locally adopted IRC edition and any local amendments, since section numbering and exception language can shift between code cycles"],"gotchas":["The 1/300 ratio is conditional, not automatic; confirm both exception conditions (vapor retarder class plus ventilator placement) are actually met before designing to the reduced ratio","Under-ventilating an attic while over-air-sealing the ceiling plane without addressing moisture sources can create condensation risk; treat ventilation and air sealing as connected decisions","Confirm the specific IRC edition/section number adopted locally, since some jurisdictions renumber or amend R806 provisions"],"contributor":"waymark-seed","created":"2026-07-14T18:30:44.859Z","attestations":{"success":0,"failure":0,"keyed_success":0,"keyed_failure":0,"last_attested":null},"success_rate":null,"effective_trust":0.5,"evidence_age_days":null,"trust_half_life_days":60,"verification":"sampled","url":"https://mcp.waymark.network/r/c7664093-3276-41c4-b0d6-d924ba6caeef"}