On my trip to Aspen, Colorado last week, when I learned to ski, I noticed an interesting snow pattern on a lot of the roofs of the houses near where we stayed. Not being from snow country, I didn't know what they were. In fact, when I posted the lower photo in this article to Facebook, my friend Nate Adams of Energy Smart Insulation wrote, "Heat cables? Are you going to make me come down there?"
I just thought that was an interesting snow melt pattern. Turns out, that interesting pattern is because of the heat strips installed on the edge of the roof to melt snow and ice dams. Who knew?! The photo above shows pretty clearly that something unnatural is going on. In the photo below, it's not really so clear to someone who's not familiar with roof heat strips. (Well, that's my excuse and I'm sticking to it!)
But why are they up there anyway? The aforementioned Nate Adams wrote a guest post on icicles and ice dams for us back in January, so I'll let you go back and read that for a fuller explanation. The short answer is that, much of the time, the snow melts above the the conditioned space because of excessive heat loss from the house. The water then drains down the roof and refreezes at the eaves.
The real solution is to fix the heat loss problem with air sealing and insulation. Because so few people seem to understand basic building science, they install heat strips instead. But hey, they're 100% efficient! And if you have a house in Aspen, paying for electricity is certainly not a concern. They even heat most of the sidewalks in that town.