The issue (ice dams) is caused by bad architecture, specifically the shape of the roof and/or the design of the house’s thermal envelope.
A properly designed roof should not have ice dams because the whole roof should get uniformly cold (below freezing) when the air temperature drops and the roof itself should not have any areas where meltwater can gather and refreeze.
My house violates both of these criteria. It has 2 different roof lines that meet at a right angle, resulting in a saddle point where tons of meltwater can gather. It also has a leaky thermal envelope that causes snow and ice to melt higher up on the roof and then refreeze in the gutters (which will always be cold because they hang outside the thermal envelope).
An ideal roof has a single roof line (think of a simple rectangular house with one peak in the middle) and the roof itself is raised several inches above a secondary plywood roof enclosing the insulation (with the thermal envelope inside) and ventilation allowing cold outdoor air to circulate between the two layers. This gives a pretty uniformly cold roof that maximizes drainage uniformity (no gathering of meltwater until the gutters). As long as the gutters and downspouts are free of clogs there should be no issues with ice dams.
The issue (ice dams) is caused by bad architecture, specifically the shape of the roof and/or the design of the house’s thermal envelope.
A properly designed roof should not have ice dams because the whole roof should get uniformly cold (below freezing) when the air temperature drops and the roof itself should not have any areas where meltwater can gather and refreeze.
My house violates both of these criteria. It has 2 different roof lines that meet at a right angle, resulting in a saddle point where tons of meltwater can gather. It also has a leaky thermal envelope that causes snow and ice to melt higher up on the roof and then refreeze in the gutters (which will always be cold because they hang outside the thermal envelope).
An ideal roof has a single roof line (think of a simple rectangular house with one peak in the middle) and the roof itself is raised several inches above a secondary plywood roof enclosing the insulation (with the thermal envelope inside) and ventilation allowing cold outdoor air to circulate between the two layers. This gives a pretty uniformly cold roof that maximizes drainage uniformity (no gathering of meltwater until the gutters). As long as the gutters and downspouts are free of clogs there should be no issues with ice dams.