That house doesn't have enough insulation. How did I know that?

How do you know if there is enough insulation to keep heating dollars from flying out of the top of your house? On days like today, it is pretty easy. It is January. We had snow about a week ago. Today, it is 44 degrees out.

Today, while I was driving through Needham, I noticed a house with significant snow cover on the roof. The house with a full complement of snow stood out. Other houses on the same street had bare roofs. That house has good insulation.

Sunlight melts snow, eventually, even when the air is below freezing. But, most of the time, snow is melted from heating dollars at work. House heat will rise right through the roof unless there is insulation to stop it.

Insulation on the floor of an unfinished attic is a great energy saver. It is a no-brainer that pays back fast. If you have a finished attic space, insulation is just as important. However, it is a little trickier because you need to insulate and ventilate in the roof space above the finished rooms. Fresh air needs to get into the bottom side of the roof surface and a blanket of insulation needs to stop the house’s heat from passing up through the roof. A baffle between the air space and the insulation is the way to do that. Failure to insulate can lead to a nasty mold problem. (More about that another day.)

If you are a buyer, what should you look for? On a day when snow is on some rooftops, look at a house you are considering. If it is the only one without snow, there is not enough insulation. If you can see the lines where the roof rafters are causing less snow melt, there is not enough insulation. (It will look like stripes of deeper snow with patches of less snow in between.) But, if every house on the block has melted snow, it may be a sunny spot or the day is warm enough to melt most snow.

As an aside, sky lights melt snow fast because they insulate much less than roof material. Consider getting an insulated shade for your skylight.