Home moisture problems

The Old House Web

Here aresome tips on diagnosing and correcting moisture problems. Parts of this story: ~~Introduction~~ Attic andmechanical ventilation ~~ Houseson crawl spaces and other moisture sources ~~ Caulkingand weather-stripping ~~ Basementwall condensation problems


The installation of taped, insulating sheathing that acts as an air barrier to increase efficiency and provides rain drainage eliminating the need for building paper or housewraps.
Photo: Sara Farrar

Finding solutions to moisture problems, be they condensation or water problems, is often a difficult,time-consuming and expensive undertaking.

  • The first step in any situation is to identify the source of the problem. This may not be easy because two and often more things may be working together to create the problem.
  • Once you know the source, rethink the basics about condensation and/or water problems. What are the no-cost or low-cost solutions you can try first? Can the solution(s) attempted help you in other ways in addition to solving the moisture problem? The addition of storm windows, for example, can cut heating costs as well as help prevent fogging or icing of windows. In such a case,the cost of the solution may be well justified.
  • In some cases, you may find you have to rely on outside help,such as contractors, engineers or architects. Do look into the backgrounds of these people to ensure that you are getting the best help available and that the solutions they offer will indeed solve the problems.

Three conditions that increase the likelihood of condensation problems

Practices that trap heat in a house also trap moisture and pollutants.
Graphic by Lawrence Berkeley National Laboratory

Condensation can be a problem in both winter and summer. Three conditions in the home increase the chances
that condensation will occur.

  • The first of these is a relatively recent phenomenon. Many homeowners have added insulation to cut heat loss and heat gain, while others have caulked and weather-stripped around windows and doors to reduce the infiltration of cold air into their homes. The same practices that trap heat in the home also trap
    high levels of moisture.
  • A second common condition contributing to moisture problems in homes is the existence of cool
    surfaces with which interior moisture vapor naturally comes in contact. In less energy-efficient homes, certain locations are prime candidates for condensation problems because they commonly have cool surfaces. These include poorly weatherized and insulated windows (in winter),poorly insulated exterior walls and ceilings (winter),masonry or concrete surfaces (summer), toilet tanks(summer) and cold water pipes (summer).
  • A third condition contributing to household condensation problems is excessively high humidity levels
    in the air within the home. The normal indoor humidity range in winter is 15 to 50 percent. In the summer, the humidity range may be higher because of the higher outdoor humidity levels we sometimes experience then.

Vapor sources
Moisture in homes comes from many sources.

High humidity level problems

The first step to be taken in attempting to control condensation problems is simply to reduce the level of
humidity in the inside air.

During the winter, the humidity level you will want to attempt to achieve in your home will depend on the outside
temperature. As outside temperatures drop, you need to lower inside relative humidity levels to minimize

Monitor the interior surfaces of double-pane windows during winter. If running water (condensation) is
apparent on them, the interior relative humidity level is too high and should be lowered.

Levels to achieve in summer are somewhat more arbitrary---they depend mainly on how uncomfortable you
are in high humidity conditions.

recommended humidity levels

Summer problems

During the summer, one of the major functions of an air conditioner, in addition to cooling warm interior air, is removing humidity from the home. A second alternative available to lower summertime humidity levels is to purchase and operate a dehumidifier. If humidity levels remain high in winter, you may need to run it then, too.

Though both air conditioners and dehumidifiers are effective solutions to excessive moisture problems,they are relatively expensive to buy and costly to operate. Expect increases in your electricity bills during the months you use them.

The informationin this article comes from Michigan State UniversityExtension bulletin E-2109, Moisture Problems in the Home.

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