Preventing Condensation

Today's homes are designed and built with energy efficiency in mind.  This can increase the homeowner's comfort level and reduce the utility costs.  However, exceptionally "tight" homes with a significant number of moisture sources can provide opportunities for moisture buildup including window condensation.

Uncontrolled moisture, over time, can cause chipped and peeling paint, warping and swelling of wood around windows and can cause drywall and wallpaper damage.

When moisture is properly controlled, homeowners can enjoy the increased energy efficiency of a tight home while avoiding moisture problems.

What is condensation and why does it occur?

During cold weather the typical household releases 3 gallons of water vapor each day through normal indoor activities.  Some of the most common sources of indoor moisture are cooking, washing clothes, ironing, watering plants, cleaning, dishwashing, bathing, unvented kitchens and the number of household members.  Even small items like leaving the toilet seat up allows moisture to collect in your home.

During cold weather, much of the moisture created inside the home will migrate toward the colder outside walls, floors, and roof.  Condensation occurs when water vapor in warm air comes in contact with a cooler surface.  It is most often seen on window frames and glass (due to being made of non-porous materials), but condensation can occur within walls, the attic, and the crawlspace, where it is less likely to be noticed.

The first step in controlling condensation is to determine if your home has a high concentration of moisture and identify the areas where moisture is lingering.  A thorough moisture audit of your home will alert you to possible high-moisture areas.
 
One way to determine if overall indoor humidity levels are too high is to use a few relative humidity indicators.  These are inexpensive devices, installed near the thermostat that approximately measure the relative humidity in the house.  If the relative humidity is higher then the values shown in the table for the particular outside air temperature, the home has excess humidity and a greater potential for moisture problems.

Other indications of moisture can be discovered by checking through the house for certain symptoms.  Some of the typical symptoms of lingering moisture are detailed below:

• Mold and mildew; this can indicate moisture damage and decay.
  
• Odors; more intense with high humidity, they may indicate mold or mildew hidden from view.
  
• Damp feeling; dampness is especially noticeable in unheated areas such as closets and in the crawlspace.
  
• Fogging or Icing windows; condensation that does not disappear during the day indicate high humidity or the need for additional insulation or air movement.

If a moisture problem is present there are several possible solutions.  These include reducing or eliminating the source of the moisture, and providing proper ventilation.

Probably the easiest and least expensive way to solve many moisture problems is simply to reduce or eliminate the source of the moisture.  Other means of reducing moisture sources may not be so obvious.  For instance, one of the major sources of indoor humidity is people.  Every time a person breathes, the lungs expel moisture and heat.  Water vapor also comes from perspiration on the skin.  Too many people in a small space can cause excessive moisture inside a house.  Homes should contain no more then one occupant for every 250 square feet of living space.  This ratio includes pets, as well as people.  If a family of four with a pet or two lives in a 1,000 square foot home, there is a high risk for moisture problems.

Speaking of pets, aquariums can be a major source as well.  Be sure to keep the cover on the tank as much as possible. 

Humidifiers are often used to increase comfort and avoid dry skin in the winter, but they can compound moisture problems.  Use humidifiers only when necessary, and decrease or eliminate their use if moisture problems are found in your home.
 
Bath and Kitchen: Increased circulation is especially necessary in the bathroom and kitchen, two typically high moisture areas.

Bathing, shaving and allowing towels to dry indoors create a great deal of moisture in the bathroom.  Low-volume shower heads can save energy, but they generate greater amounts of water vapor.  The bathroom should be vented to the outside, and exhaust fans should be used.  Exhaust fans should be run for a period of time after completion to ensure elimination of moisture.

Kitchen moisture sources include cooking, open-flame heating and cooking appliances, cleaning, dish washing and laundry.  As with the bathroom, the kitchen should be vented to the outside and exhaust fans should be used or the kitchen window slightly opened to allow moisture to escape.  Exhaust fans should be run for a period of time after completion to ensure elimination of moisture.  Other tips for controlling moisture include:

• Cook with lids as it keeps both heat and moisture in.
  
• Vent clothes dryers outdoors as it not only reduces moisture, but also reduces the chance of indoor pollution due to lint and laundry products.
  
• Use a fan or open a nearby window to increase ventilation when mopping floors or washing dishes.

Window Coverings: Window blinds, heavy drapes, wooden shutters and shades can add warmth and beauty to your home but can cause severe problems during the winter months if left in a closed position during times of extremely cold.  If there is any trapped moisture in the air between the inside face of the window and the window covering, it can turn into condensation or ice because it is blocked off from warm convexing air inside your home.  When the window covering is finally opened, the warm air inside your home will rush toward the window and come in contact with the window frame and inside surface of the glass.  This abrupt collision often causes condensation to form on the window frame and glass.  It is a good idea to open window coverings to allow this "pocket" of air to breathe to prevent condensation.

Heating Systems and Appliance Problems: Flame-fired heaters and appliances used for cooking or water heating can be a major source of moisture.  A properly operating gas burner gives off water vapor and carbon dioxide; however, faulty systems or ones that do not receive adequate combustion air can emit even more water vapor and carbon monoxide gas into the living area.  Incomplete combustion is revealed by excessively yellow or wavy flames.

Flame-fired heating systems and appliances should be checked regularly.  If you use a fireplace or wood stove, be sure to let the firewood dry outside if possible.  Wood allowed to dry inside the home can add moisture to the air.

Plants: In addition to the moisture that evaporates from potting soil, plants release moisture into the air through transpiration.  An attached greenhouse can be source of moisture problems, especially in the wall to which it is attached.

Avoid over watering plants.  They actually require lower relative humidity levels than many people think.  Be sure to provide adequate ventilation in areas with lots of plants.  Keep greenhouses closed off from the rest of the house, and provide proper exterior drainage.

Air and moisture from a more technical point of view

The air we breathe is really a mixture of two invisible gases; dry air and water vapor.  Each of these elements may act independently, but they also act together.

For example, the amount of water vapor that can be contained in a given volume of dry air depends upon the temperature of that air, the warmer the air, the more water the air can hold.  Consider a room with a volume of a thousand cubic feet (10'x12. 5'x8'). With the air at a temperature of 75 degrees F, the room can contain as much as 1.4 pints of water (in vapor form), but if the air is at 45 degrees F, it can hold less than a half-pint of water.

The moisture content of air is generally given in terms of Relative Humidity.  As an example, 50% relative humidity means that the air is holding half that amount of water vapor that it could hold.  Unfortunately, this method of indicating moisture content in the air is misleading, because it does not give a true picture as the actual amount of water in the air.  For example, air at 30 degrees F with a relative humidity of 80% contains about half as much moisture as air at 70 degrees F and 35% relative humidity.  This is because, as mentioned above, warm air can hold more moisture than cold air.  It also shows how bringing in cold outside air will reduce a moisture problem- the outside air is usually much dryer in terms of actual moisture than indoor air, and mixing it with the moist room air will lower the relative humidity in the room.

At 100% relative humidity the air contains all the moisture that it can hold and is said to be saturated.  The dew point temperature of a moist air mixture is the temperature at which saturation is reached and condensation first begins to appear.  Condensation occurs when moist air touches a surface that is colder than the dew point of the air.  If the cold surface is below freezing, the condensation will appear as frost.  A common example of condensation is the water or frost which appears on windows in cold weather.  Winter condensation and moisture problems are most likely to occur in climates where the average January temperature is 35 degrees F or colder.  Where average winter temperatures stay above 35 to 45 degrees F, condensation does not seem to be a problem.