Attic Humidity In Winter

High humidity in an attic is usually caused by air leaks in the ceiling of the top floor of your house.

Attic humidity in winter.

This reduces attic moisture. Frost itself doesn t do any damage but once it melts things get wet and then damage occurs. To start frost accumulates when moisture laden air from the house gets into the attic. Eliminating mold and mildew on the roof structure is the ultimate goal.

Our main concern in the winter is moisture. Hot summer weather poses the opposite problem for maintaining recommended attic temperatures. If there is excessive moisture accumulation in your attic it will condense on cold areas mainly on the underside of your roof deck. Only about 10 of the hip roof is shaded so it gets plenty of direct sunlight.

Sealing the attic shut for the winter appears to effectively stop the air flow the major source of moisture accumulation. Quelch the heat wave. Winter air is by nature not humid so the problem must be condensation related. During the winter months the recommended relative humidity inside a house is anywhere between 30 50 percent.

When it comes to humidity you would be best to have the levels below 50 to avoid mold growth and structural rot. Warm and humid attic air combined with cold outside temperatures leads to condensation which can form on any cold wood surfaces metal nail heads chimney surfaces ventilation pipes and even in the insulation. Some initial moisture will leak in but with no air escaping from the attic neither air flow nor air changes it will soon stop leaving only a light frost on the underside of the roof. With outside temperatures ranging between 5 f and 95 f attic temperatures range between 48 f and 92 f.

That s about it pretty simple. Cold outdoor temperatures especially below freezing can wear on your furnace. The results are that the attic temperature is close to the outside temperature but the relative humidity is significantly higher in the attic than either the indoor or outdoor readings. So the first step is to seal the air leaks.

In winter the humidistat operates the attic fan when the relative humidity exceeds a preset level usually 40 to 50. Ideal attic temperature and humidity settings cold outdoor temperatures affect attics. In summer the thermostat operates the fan when the attic temperature reaches a preset level usually 90 to 95 degrees f. During winter months humidity from this escaping air can condense on cold attic surfaces leading to mold.

When moisture gets into the attic it condenses on the roof sheathing in the form of frost.