Why Ice Dams Cause Interior Leaks | ROOFNOW™

Why Ice Dams Cause Interior Leaks

Part of the ROOFNOW™ Roofing Knowledge Center

Ice dams are a common cause of winter roof leaks. While they form at the roof edge, the resulting damage often appears inside ceilings and walls.

Key concept: Ice dams trap water where roofs are not designed to hold it.

How Ice Dams Form

Ice dams form when snow melts on warmer roof surfaces and refreezes at colder edges. This creates a ridge of ice that blocks normal drainage.

Why Water Backs Up Under the Roof

Once drainage is blocked, meltwater pools behind the ice dam. This water can move upward beneath roofing materials, bypassing normal water-shedding paths.

How Water Reaches the Interior

Water entering under the roof covering follows decking seams, fasteners, and framing until it finds a low point. The visible leak often appears far from the ice dam itself.

Why Ice-Dam Leaks Are Intermittent

Ice-dam leaks depend on temperature. Leaks may stop during cold periods and reappear during daytime melting or warm spells.

Inspection reality: Ice-dam leaks are drainage failures, not surface roof leaks.

Why Temporary Fixes Often Fail

Removing surface ice or patching shingles does not address water backup or movement beneath the roof system.

For deeper explanations, see:

Summary: Ice dams cause interior leaks by blocking drainage and forcing water under roofing materials. The damage appears inside only after water travels through the roof system.