Entretien extérieur de bâtiment
How is an ice dam formed?
Many factors are involved. Here are two common scenarios.
1- Insufficient ventilation and insulation in the attic lets heat escape and warm up the roof sheathing from underneath, melting the snow above it.
2- The resulting meltwater flows down the roof then freezes at its edge, where it is not warmed by heated space underneath.
3- The dam builds up as snow melts and freezes again. Water starts to accumulate behind the dam.
4- Water makes its way underneath the shingles or elsewhere and penetrates the house.
Source: Canada Mortgage and Housing Corporation
1- Snow accumulates on roof.
2- Temperatures warm up, snow melts and meltwater flows down the roof.
3- Temperatures cool down. Ice starts to build up.
4- Temperatures warm up again. Meltwater or rain accumulates and is trapped underneath the ice. Infiltration ensues.