Ice Dams and Attic Ventilation: Why Your Roof Needs to Breathe

Southern Indiana does not get the deep, long winters that northern states do, but we get plenty of freeze-and-thaw cycles, and that is enough for ice dams to form on some homes. The good news is they follow a predictable pattern, and the fix usually starts in the attic.

How an ice dam forms

Heat from the house leaks into the attic and warms the roof deck. Snow on the upper roof melts, runs down toward the colder eaves, and freezes again. Over time that ridge of ice grows and can back water up under the shingles.

Warning signs

• Thick icicles along the eaves or a ridge of ice at the roof edge
• Water stains on ceilings or walls near the exterior of the house
• Frost or moisture on the underside of the roof deck in the attic
• Snow that melts in patches while the rest of the roof stays covered

The three things that usually matter

Air sealing keeps warm air from leaking into the attic through gaps around lights, hatches, and wiring. Insulation slows the heat that does get through. Ventilation moves air across the underside of the roof so the deck stays close to outdoor temperature. They work together, and improving one without the others may not solve the problem.

Intake and exhaust have to balance

A common design pulls air in at the soffit and lets it out near the ridge. If the soffit vents are blocked by insulation or the exhaust is undersized, air cannot flow the way it is supposed to. A quick look at your soffits from the ground and at the attic edges from inside can tell you a lot.

Fix it before winter

Gerkin Construction can look at your roof and attic together and tell you whether ventilation is part of the problem. Fall is the best time to have that conversation, well ahead of the first freeze.