Page 101 - 2018 National Home Improvement

2018 National Home Improvement Estimator, All Rights Reserved Page 81

Vapor Barrier
Good insulation cuts heating costs and adds to comfort by making the temperature in the house more
uniform. But simply adding insulation to an old home can create more problems than it solves. In
poorly-insulated older homes, water vapor escapes to the exterior without interference. But in a tighter
home with fewer air leaks and better insulation, water vapor tends to collect in walls. There, it cools and
condenses into liquid. The result can be saturated insulation and siding. Running a humidifier, cooking,
bathing, and simply breathing aggravate the problem. Liquid moisture in a wall reduces the effectiveness
of insulation, promotes decay and supports the growth of mold. To control moisture problems, be sure
there is a vapor barrier on the (winter) warm side of walls and ceilings.

Most homes built before the mid-1930's don’t have a vapor barrier in either the walls or the ceilings. If
attic insulation has been upgraded since construction, you’ll probably find batts or blankets with a Kraft
face that resist the passage of moisture. The Kraft face should face down, against the ceiling finish. But
if the ceiling insulation is loose fill, there should be a separate vapor barrier of coated paper, aluminum
foil, or plastic film below the insulation.