Using Light Snowfalls to Track Heat Loss

One thing that light snowfalls are good for, other than brightening the day by recycling light, is to find out where your attic needs more insulation. If the roof remains white long after the snow, it suggests that the insulation is uniform and thick. A quick melting compared to neighbors' houses suggests a lot of heat is getting lost through the ceiling of the top floor either through poorly designed recessed lighting fixtures or inadequate insulation (a steep roof can also affect how long snow remains).

The melt pattern in this photo is from my own roof. There are two small spots where the snow is melting faster. The bigger one coincides with where a heat vent is close to the ceiling in the bathroom. Adding more insulation to that spot is tricky, because one has to squeeze in close to the rafters in the attic, and be sure not to stuff insulation so far in that it touches the roof boards and cuts off airflow needed to keep the boards dry.

A 2008 post on this subject offers more melt patterns, and has a useful comment by a reader about the problem with recessed lighting.