Using snow to see heat transfer

Education Energy & Sustainability

In these photos, you can see the heat transfer happening through a number of roofs in my neighborhood. In a wintery time like we have now, the snow acts as an indicator of your insulation. If you have a full roof of snow, then you’re well insulated. If you have spots of bare roof surrounded by snow, then inside the house is an area where it’s uninsulated, or poorly insulated. If your roof doesn’t hold the snow at all, then it’s time to look at your attic insulation. Sunny, South facing roofs will naturally clear faster on clear days, due to the input of solar energy. Any part of your building envelope that transfers heat is spending your money and wasting energy resources.

On some of these roofs, you can see areas of white lines. These are the rafters. The roofing structure is thicker there, and heat isn’t transferring as well in those spots. A nearby antique cape, shows that the rafters are 3 or 4 feet apart. That is a big difference from the way it would be framed in modern times with the rafters at 16 inches on center.

One neighborhood house sports a chimney from a woodstove. It seems that the rafter bay where the chimney pierces the roof is totally uninsulated, judging from the lack of snow on that one section of the roof.

On my house, you can see thin spots about two feet from the gutter. That is the place where the studs from the wall meet the rafters. This unusual framing technique seems to have been done to save on materials when building the house. The wall is well insulated, as is the attic. Its just the junction point that is radiating heat.

Before this winter, there were three bare spots on a section of roof over the mudroom in my house. I noticed these spots, and really noticed the cold air flowing from the recessed lights in that room. For a few winters, I put up insulating window plastic over the fixtures to keep the warm in and the cold out. These lights have since been removed and the cavities insulated, there is still a bit of melting in those locations, but nothing like it was.

What can you see by looking at the exterior of the houses around you? Can you see the energy flowing from warm to cold? Does this help you see improvements you can make to your house?

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