We got a couple inches of snow here in Atlanta over the holidays. That always offers a great look at heat loss through the ceiling, so I love to get outside and take pictures. After the snow has been on the rooftops for a day or so, the quality of the building enclosure is easy to see.
In the lead photo above, you can see what happened after that snow had been on the roof for only 12 hours. Near the ridge, the snow had all melted. Farther 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 photo below shows another building in the community with the same problem.
These buildings are in the condo complex where I live, and there’s a lot of heat loss to the attic. The building envelope 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. That heat then melts the snow on the roof.
By contrast, the building below, also in our community, shows little evidence of melting snow. This is what all the roofs in the community should look like.
One serious problem that can occur in areas where you have significant accumulations of snow on the roof is ice dams and icicles. 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. You can see the ice dam at the roof’s edge in the photo below, with huge icicles hanging below it.
Who needs an infrared camera when you’ve got snow!
Allison A. Bailes III, PhD is a speaker, writer, building science consultant, and the founder of Energy Vanguard in Decatur, Georgia. He has a doctorate in physics and writes the Energy Vanguard Blog. He is also writing a book on building science. You can follow him on Twitter at @EnergyVanguard.
Comments are closed