Last reviewed October 31, 2026.
It is August, the upstairs bedrooms will not drop below 80 at night, and the roofer measuring for a new roof climbs into the attic and comes back down sweating. The way an attic breathes affects how hot the second floor gets, how long the shingles last, and whether the shingle warranty pays out.
How much venting New York requires
Section R806 of the 2025 Residential Code of New York State, in effect since December 31, 2025, sets the rules for a vented attic:
- Cross ventilation for each separate attic space, through openings that keep out rain, snow, birds and rodents.
- 1/150 of the attic floor area as net free ventilating area. A 1,500 square foot attic needs 10 square feet of open vent area.
- 1/300 is allowed when 40 to 50 percent of that area is in vents in the upper part of the attic, no more than 3 feet below the ridge, and the rest is in the bottom third. (In the coldest climate zones the code also requires a vapor retarder for this.)
- At least 1 inch of air space between the insulation and the roof deck at the vents, so insulation never plugs the soffits.
- Vents installed to the manufacturer’s instructions.
The same code allows an unvented attic, but only when the attic is fully inside the insulated envelope, for example with air-impermeable insulation such as spray foam applied directly to the underside of the roof deck. That is a different job from a reroof and needs its own design.
Intake at the eaves, exhaust at the ridge
Every ventilation system has two halves. Air comes in low, through soffit or eave vents, and leaves high, through a ridge vent or roof vents. Owens Corning says the key is having the correct amount of both, and that an uneven mix leads to pressure problems. Lomanco recommends a 50/50 split, with intake meeting or slightly exceeding exhaust.
Lomanco’s own example: a 2,000 square foot attic at 1/300 needs 960 square inches of net free area, 480 for intake and 480 for exhaust. Every vent is rated in square inches of net free area, so ask your roofer for the count and the math, not just “we’ll add some vents.”
Why mixing vent types backfires
Air Vent says it is never OK to mix two different types of exhaust vents, such as a ridge vent with box vents, gable louvers or a power fan, in a common attic. Lomanco explains why: with different exhaust vents, one can end up acting as the intake for the other, so air short-circuits across the top of the attic instead of sweeping up from the eaves. Lomanco gives the same rule and adds that all exhaust vents in one attic should sit at the same height.
It is worth asking about on a reroof. If your quote adds a ridge vent to a house that already has box vents or gable louvers, ask whether the old exhaust vents are being closed off.
Powered attic fans and bath fans
A powered attic fan sounds like a fix for a hot attic, but the Department of Energy’s Building America Solution Center says studies indicate these fans often cause more energy loss than they save. They pull the attic into negative pressure, which drags conditioned air up through ceiling gaps and can backdraft gas appliances that are not sealed combustion. Owens Corning says any powered fan needs enough intake to balance it, or it pulls air from the living space.
Bathroom and kitchen fans are the opposite problem. The state code requires them to discharge outdoors and bars them from dumping into an attic, soffit or ridge vent. A bath fan duct that ends loose in the attic puts warm, wet air right against the cold roof deck.
Signs your attic is not breathing
Owens Corning lists dampness, water stains or frost on the underside of the roof deck, rusted nail tips and electrical boxes in the attic, a wavy roofline from moisture-damaged decking, and heating and cooling bills creeping up without a reason. Anthony’s Roofing in Bohemia adds very hot rooms in summer, musty smells or mold, and shingles that curl or crack early. A roof inspection should include a look in the attic for exactly these.
The ventilation clause in your shingle warranty
Shingle makers put ventilation in writing. Owens Corning’s standard limited warranty excludes “damage caused by improper or inadequate roof ventilation,” and its Preferred Protection warranty requires the roof to be installed over a ventilated deck and states that failing to install adequate ventilation is not an application error by the manufacturer.
In other words, if the shingles cook from below, the claim can be denied. That is the best reason to get ventilation written into a roof replacement contract: the vent types, the net free area for intake and exhaust, and what is being closed off.
Air sealing, insulation and PSEG rebates
Ventilation works best over a sealed, insulated ceiling, and that part of the job can qualify for money back. PSEG Long Island’s 2026 Home Performance program lists rebates of $2,500 for insulation and $1,000 for air sealing at the market-rate tier, with higher amounts for moderate and low income households. Insulation has to go in with blower-door-assisted air sealing. The program starts with a free whole house energy assessment through a participating contractor, which includes a blower door test and a thermal scan.
