Ice Dams: Identification, Prevention, Removal

An ice dam is a ridge of ice that forms at the edge of a roof and prevents melting snow from draining. As water backs up behind the dam, it can leak through the roof and cause damage to walls, ceilings, insulation and other areas.

How do ice dams form?

Ice dams are formed by an interaction between snow cover, outside temperatures, and heat lost through the roof. Specifically, there must be snow on the roof, warm portions of the upper roof (warmer than 32° F), and cold portions of the lower roof (at freezing or below). Melted snow from the warmer areas will refreeze when it flows down to the colder portions, forming an ice dam.
Gutters do not cause ice dams to form, contrary to popular belief. Gutters do, however, help concentrate ice from the dam in a vulnerable area, where parts of the house can peel away under the weight of the ice and come crashing to the ground.

Problems Associated with Ice Dams

Water intrusion caused by ice dams can contribute to rotted roof decking, respiratory illnesses (allergies, asthma, etc.) caused by mold growth, reduced effectiveness of insulation (wet insulation doesn’t work well), and peeling paint. This may happen long after the ice dam has melted!


Prevent ice dams by keeping the entire roof cold. This can be accomplished by sealing up all air leaks to the attic, or removing snow  from the roof. (Be sure to do this safely – use a roof rake from the ground).

Prevention and Removal Methods to Avoid

What not to do – don’t try manually removing the ice!  It’s tempting to grab a shovels, hammer, ice pick, rake, or whatever destructive items can be found in the shed. The roof can be easily damaged by these efforts, as can the homeowner, when they slip off of the icy roof.