Energy Vanguard Blog

Snow on the Roof - The Poor Man's Infrared Camera

Posted by Allison Bailes on Wed, Jan 5, 2011

We got a couple inches of snow here in Atlanta over the holidays, and I love to get outside and take pictures after the snow has been on the rooftops for a day or so. In the photo below, you can see what happened after that snow had been on the roof for only 12 hours.

roof snow melt attic heat loss insulation air barrier

Near the ridge, the snow has all melted. Further down, you can see the outline of where the rafters are. At the eave, the snow is as thick as it had been all over the roof when the snow first came down.

The reason is that in this building, one of the buildings in the condo complex where I live, there's a lot of heat loss to the attic. The building envelope - the air barrier and insulation - is supposed to keep the heat in the house. If, however, there are air leaks through the ceiling or the insulation is inadequate or both, the home loses heat to the attic, and that heat melts the snow on the roof.

By contrast, the building below, also in our community, shows no evidence of melting snow.

snow on roof heat loss air barrier insulation

One serious problem that can occur in areas where you have significant accumulations of snow on the roof is ice dams. When that snow on the roof melts, it runs down to the eave as liquid water. At the eave, it's not being heated from below anymore, so it refreezes, as shown below. I've heard of one huge ice dam that fell off a house in New Jersey and crushed a car below.

Ice dams at the eave from heat loss in the attic due to a weak building envelope

Who needs an infrared camera when you've got snow!

 

Related Articles

When It Comes to Ice Dams, You CAN Fix Stupid!

Be a Controlling Building Enclosure Control Freak with Control Layers

11 Building Science Secrets Every Home Builder & Remodeler Should Know

Tags: building enclosure, insulation, air leakage, attic