Icicles: Are our roofs too warm to retain snow?

 

Sliding snow from roof after Dec. snow storm

Are you living in a unit with a mansard or a gabled roof? Then chances are that after the recent snow storm you’ll have to struggle with icicles hanging from the roof ridge and gutters. Icicles form when the snow on the roof melts and begins to trickle down. The sunny day after the storm may account for some of the melt, even if air-temperatures have been constantly below freezing. You will observe however that the snow tends to slide away in big blocks .

 

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Some neighbors even report ‘avalanches” coming down from their roofs. How does this happen? The answer is that it is the roof that heats and melts the base layer of snow. This causes the snow cover to slide away on the slippery base just like a piece of butter would slide on a hot pan. Icicles and ice dams build up where decades of neglected insulation allow heat to escape and warm-up the slate shingles. Our roofs are simply too warm to hold the snow long enough so that it can melt without the problems we are currently having. It takes a couple of snow storms to actually  “see” the heat -and money- loss through our roofs.

Flat roofs don’t perform any better (they are actually less efficient). We just don’t “see” the effect.

 

Snow cover slides away in one block after Feb. snow storm

 

Snow sliding from the roof after the Dec. Snow Storm

 

Same date and time as above: Another building retaining the snow on the roof: better insulation.

 

Neighboring building after the Dec. snow storm: Compare the roofs.

 

Private Home at S Edgewood and 13th St.: Well insulated attic!

 

Snow sliding away during the Feb. storm. Subfreezing temperatures. NO sun!

 

Same date and time as above. Snow cover disappeared few hours after the storm. Subfreezing air temperatures. NO sun!

 

Same date/time: A look across the street: Neighbors' roofs are obviously better insulated.

 

Same as above. Neighboring roofs retain the snow longer. Less ice dam build up.

 

After the 2d Feb. storm. Combined effect of sun and not insulated roof: Big ice dams damage the roof and are a serious hazard for residents