How do I know if my attic is ventilated well?

A well-ventilated attic stays close to the outdoor temperature, has no damp smell, stained wood or frost, and has a clear path for air from the eaves up to the ridge. You can check most of this yourself from the attic floor and the ground, without touching the roof, then ask a roofer to confirm anything that looks off.

What a ventilated attic looks like

Virginia Cooperative Extension says that most building codes require roof and soffit vents to exhaust humidity and moisture that could cause insulation or other building materials to deteriorate,^[1] and that most homes should have a combination of a continuous ridge vent along the peak of the roof and continuous soffit vents at the eaves to provide the most effective ventilation.^[1] As a general guide, a home should have approximately 1 ft2 of net vent opening for every 150 ft2 of ceiling or attic space, though there are exceptions, so your local building code governs.^[1] Extension adds that if individual vents are used instead of continuous ones, the vents should be divided equally between the ridge and soffits.^[1]

The key idea is a path: air enters low at the soffits and leaves high at the ridge. Both ends have to be open.

A checklist you can do safely

Pick a dry day and use a flashlight. Stay on the attic's floor framing or a board laid across it, and skip the roof entirely.

• Look for intake. From outside, check that the soffits under the eaves have vents that are open, not painted over or covered. From inside, look at the eaves for daylight or moving air.
• Check the insulation at the eaves. Building America says baffles and insulation dams should be installed to keep insulation out of the soffit vents and to direct cooling air flow from the soffit vents up along the underside of the roof deck to the ridge vents,^[2] and that an air gap of at least 2 inches should be provided between the top of the insulation and the underside of the roof deck.^[2]
• Find the exhaust. Confirm there is a ridge vent, gable vents or roof vents, and that they are not damaged or blocked from outside.
• Read the wood. Dark staining, rusty nail tips, mold or soft rafters mean moisture has been lingering. ENERGY STAR lists moldy or rotted attic rafters or floor joists, indicating moisture problems,^[3] and wet or damp insulation, indicating a leaky roof,^[3] as reasons to hire a professional first.
• Trace the fan ducts. Bath fans, the range hood and the dryer should discharge outdoors. ENERGY STAR flags kitchen, bathroom or clothes dryer vents that exhaust moist air directly into the attic space instead of outdoors.^[3]
• Watch the seasons. Frost on the underside of the deck in winter or a hot, stuffy attic on mild days both suggest air is not moving.

A single check is a snapshot. Looking again after a cold snap and in midsummer tells you more than one visit.

Ventilation is only half of it

Air leaking from the living space into the attic undoes good venting. Building America says the most important step is to seal all of the air leaks from the conditioned space into the attic space to keep warm air from entering the attic in the first place.^[2] Ice dams are a common sign of this, and ice dams can form with as little as 2 inches of snow accumulation on a roof.^[2] See how to prevent ice dams.

When to call a licensed pro

Call a roofer if the intake is blocked or missing, the vent is damaged, or you see any of the moisture signs above. Adding or repairing ridge and soffit vents involves roof work and, depending on the job, cutting into roof or eave framing, so it is not a DIY project. Virginia's Board for Contractors defines roofing contracting as the service that provides for the installation, repair, removal, or improvement of materials common to the industry that form a watertight, weather resistant surface for roofs and decks.^[4] The Board's consumer guide says that if the work is valued at $1,000 or more, a valid Virginia Contractor's License is required for the license category in which the contractor is to work,^[5] so check the licence on DPOR's lookup first.

Ask the pro to measure existing vent area against the 1-to-150 guide, check the intake and look at where the fans discharge, and get the findings in writing. Related reading: what a ridge vent does, what repair costs in Virginia and replacing the vent with a new roof. Browse roofing repair answers and roofing repair services, or describe the job once to hear from licensed local roofers.