Older homes, even those with single glazed windows rarely had problems with condensation.Your Grandparents home was constructed in a time when little thought was given to insulation values and completely sealing the home. Oil or wood stoves were cheap to run and operate and windows and doors were not particularly tight fitting or sealed. This provided the home with lots of fresh air leaking to the inside and excess humidity was not a problem.

In newer “green” construction we have now become obsessed with sealing the home of all air leaks. We have created a moisture condensation problem for ourselves.The installation of air barriers, vapor barriers, and double or triple glazed windows has provided reduced heating costs but has also created indoor air quality problems. The air in older homes was continually being replaced with outdoor fresh air. In newer homes we have trapped the air inside.

If you are experiencing excess condensation on windows due to high humidity, then you should be concerned because this air also travels though small cracks and openings and condenses on other cold surfaces behind the walls. In the long-term this will result in structural damage, peeling paint and possibly mold issues.Condensation on interior window

What causes this condensation?

The air in the middle of your room may be at a temperature of 70 degree F. At this temperature air can hold a significant amount of water vapor. The amount of water vapor in the air at a specific temperature is referred to as the relative humidity of the air at that temperature. As this air circulates and approaches a cold window it cools down and its ability to hold water vapor decreases. When the temperature of the air reaches the point where it can no longer hold the water vapor, known as the “Dew Point”, the water vapor is released in the form of water droplets.

Where does high humidity come from?

We generate moisture during our daily activities. Cooking, laundry, showers, washing dishes and even breathing contribute to the moisture in the air. New construction materials also contain moisture when first installed and take a few years to dry out. These materials can also absorb moisture during hot, humid summers which is then released during the heating season in winter.  It is estimated that a family of four can add more than 150 pounds of water into the air per week. Moisture is also released from aquariums or fish tanks, household plants, firewood stored inside the house, uncovered sump pump openings and condensation on water lines or water tanks.

How to control humidity

The first step in reducing humidity is to identify its source. Inspect the house for any areas which could be contributing to high moisture levels. In addition to covering or removing those items such as plants and fish tanks and sump pumps mentioned above, it is important to run bathroom fans for at least 20 minutes after showering. Insulate water lines and tanks. Shut off or reduce the setting of your furnace humidifier if you have one. Run ventilation fans and crack open a window daily for at least an hour to allow fresh air into the home. Deal with any damp basement problems, roof or window leaks. Invest in a good quality hygrometer or sling psychrometer to measure humidity in the home and try to maintain the relative humidity below 40%. Keep in mind that humidity levels will change from room to room and that measuring instruments will take time to stabilize.

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