Blocked Runoff

Ends Up Inside

Even on the coldest days, melted snow can leak into your house.

Warm air trapped in the attic melts snow by heating your roof from within.

The runoff trickles down the slope to the edge ("eave"), which remains cold because it hangs over open air instead of heated attic.

The water refreezes and over time builds a wall of ice — an "ice dam" — that forces subsequent meltdown to flow back up the slope.

As the water backs up it is forced under the shingles and into your home.

Protect Your Roof

Shingles are designed to shed water, not seal the roof. Once ice makes shedding impossible, shingles can no longer keep you dry.

Keep ice dams from  forming by taking two key precautions:

Insulate Keep your attic as cool as possible by insulating  it thoroughly. The goal is to make the attic space a thermal break between inside and outside temperatures. Make sure insulation is not covering eave vents, which are vital to adequate airflow.

Ventilate Any heat that does seep into the attic should not be allowed to linger. Roof vents must be installed to draw outside air in through the eave vents ("soffits"). As  this cool air is pulled through the attic, heat and moisture will be pulled outside. Many houses were built with too few vents but additional units can be added easily.

Taken together, insulation and ventilation will keep your roof cool and your home warm and dry.