WHAT CAUSES ATTIC FROST?
Moisture is ever-present and can be invisibly carried in the ambient air within your home. Moisture vapors increase due to daily activities like cooking, laundry, cleaning, and bathing. In the winter here in the Midwest, additional moisture is often purposefully generated by a humidifier to prevent dry skin, sore throats, dry nostrils, chapped lips, static electricity, and so forth.
When this warm moist air rises into your attic space, the vapor can settle on cold surfaces, initially as tiny water droplets called condensation. This condensation will collect on various hard surfaces and, as temperatures drop, can freeze, leading to attic frost layers on roof sheathing and other surfaces.
A few seasonal cycles of this freezing moisture can damage wood sheathing, joists and lead to attic mold.
How To Prevent Attic Frost
First, check your humidifier settings. Most people will set their humidifiers up beyond 40 percent. That is too high. But you do want some moisture, so 25 percent is too low. Depending on the number of occupants, household activities, location, and the energy efficiency of your home set your humidifier between 26 and 30 percent.
Second, be sure you have ample attic insulation. Insulation will slow the rate at which warm heated air passes from living spaces below up into your attic. Keep in mind, insulation does not stop heat flow, it resists it. The “R” value of your insulation provides a measure of how resistant your insulation is. The higher the “R” value, the greater the resistance, the slower heat will pass from living spaces to your attic.
Lastly, make sure your attic has adequate ventilation. Your attic should have good intake vents (bringing outside air in) and good exhaust venting (exhausting inside air to the outside). This creates cross ventilation, keeping fresh cool air in your attic while pulling the warm moist air out. This will minimize condensation to a large degree.
Also, be sure you are not venting your dryer or bathroom exhaust fan into your attic space. Doing so will add moisture to your attic. Both should be properly exhausted outside. Click here to learn more.