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Controlling Humidity In Your Home - Part 4

High Humidity Level Problems

Summer Problems

Houses With Crawl Spaces

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 condensation.

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 Relative Humidity Levels At Indoor Air Temperatures

Indoor Air Temperature
Outdoor Air Temperature - °F

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.

Houses With Crawl Spaces:

With homes that are built above crawl spaces, evaporation of moisture from the earth is a major source of household humidity. The high levels of humidity in crawl spaces can be a problem in both summer and winter. Foul odors in the home or crawl space, mold and mildew growth in the interior of the home (especially in closets) and growth of fungi in the crawl space itself are signs of the problem. Covering the crawl space ground with a vapor retarder (polyethylene or heavy plastic sheets available at lumberyards), as shown in Figure 1, is crucial in preventing moisture problems in crawl space homes.

crawl space condensation
Figure 1 - Preventing condensation caused by crawl spaces

In addition to a vapor retarder covering the ground, crawl spaces should be provided with adequate natural ventilation to facilitate air movement throughout the space. If a vapor retarder is present in the crawl space, 1 square foot of free vent area is required for every 1,500 square feet of crawl space ground area. Without a vapor retarder present, 1 square foot of free vent area is required for every 150 square feet of crawl space ground area. Most crawl space vents include louvers and/or screens to prevent the entry of insects and small animals. These coverings slow air circulation and cut down on the vent's effectiveness. Thus, you will need to double the amount of ventilation needed in most cases to compensate for this reduction. Locate vents near corners and across from one another to facilitate air movement through the crawl space.