Hugh Cairns: Attic frost

When conditions are ripe, it is possible to observe frost in small areas and in areas where air circulation may not be the best. Photo: Contributed – (Hugh Cairns)

Q. How much attic frost is too much?

A. After sticking my head into hundreds of attics every year, I can tell you that seeing some frost low on the underside of the roof sheathing in the dead of winter is nothing to immediately concerned about. In fact, most people don’t even know that it happens or where to look for it.

There are telltale signs of humidity retention in attic spaces. From stained sheathing to rusted nail heads. When conditions are ripe, it is possible to observe frost in small areas and in areas where air circulation may not be the best. It’s not ideal, but it can be expected, especially in older homes. It might surprise you that I’ve seen this condition in newer homes that utilize today’s ventilation and proper insulation and air/vapour barriers.

In the case of this home, the winter weather had been pleasantly mild. Next, a significant drop in temperature happened which immediately dropped temperatures to well below freezing and an abnormal amount of humid air in the attic space the moisture quickly condensed on the underside of the sheathing and froze.

It is good practice to periodically peek in your attic, and do some maintenance to improve air sealing and ventilation; I wouldn’t lose sleep if you see small amounts of frost in a few locations.

In short, if you see moderate to large areas of very thick frost in your attic, then action may be needed. Otherwise, a few small spots near an old chimney or small gaps above interior partition walls are nothing to worry about.