Here in Minnesota ice dams are a big concern. This year with some areas of the state having over 100 inches of snow, the ice dam contractors are out in force. The public discussion usually revolves around gutters, no gutters, and electric cables.
I have found that ice dams are worse with under-insulated and improperly ventilated roofs. However, we cannot completely eliminate ice dams. I have built well insulated (R-50 and above) and properly ventilated roofs. Even with adequate insulation there will be a difference in temperature between the eave and the roof area over the house. On the south side, with the temperature below zero there is snow melt on the roof, which freezes on the eave.
Code around here requires six feet of ice and water shield at the eave. This is not enough. On most house we build, we put ice and water shield on the entire roof and also upgrade the shingles.
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Thomas Fabick AIA
Fabick Architects & Builders
Mound MN
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