Attic Ventilation for Wisconsin Homes

The goal

In winter, a cold attic keeps snow on the roof from melting unevenly. In summer, moving air carries heat out so shingles don't bake.

Intake and exhaust

Air should come in low at the soffits and leave high at the ridge. Both are needed; one without the other doesn't work.

Signs of trouble

Frost on nail tips, water stains on the roof boards, mould, rusty nails, ice dams and a scorching attic in July.

Illustration (AI-generated)

Air leaks

Warm, moist air rising from the house is the main cause of attic frost. Seal around light fixtures, bath fans, plumbing stacks and the hatch.

Bath fans

Make sure they vent outside through the roof or wall, not into the attic.

Blocked soffits

Insulation stuffed into the eaves often blocks airflow. Baffles keep a channel open.

Older houses

Homes with knee walls and small attics may need creative solutions. Ask a roofer what suits your roof.

Next steps

See attic ventilation.

Insulation levels

Older attics may have only a few inches of insulation, often compressed or uneven. Topping it up after air sealing keeps more heat in the house and less on the roof deck. Keep insulation back from soffit vents and away from chimneys and recessed lights that aren't rated for contact.

Check twice a year

Look in the attic on a cold January morning for frost, and again on a hot July afternoon for heat build-up. Those two checks tell you most of what you need to know about how the attic is breathing, and give a roofer useful information if you send a request.

Moisture from below

Unvented dryers, humidifiers set too high and lots of indoor plants all add moisture that can end up in the attic. Keeping indoor humidity moderate in winter reduces frost on the roof deck.

More roofing guides

• Ice Dams in Madison Winters
• Clearing Snow From Your Roof Safely
• Cold-Weather Roofing: What Madison Homeowners Should Know
• Summer Hail and Wind in Dane County: Checking Your Roof
• Hiring a Roofer in Wisconsin: What to Check