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Dealing With Condensation Problems in Your Home

Condensation, the water forming on cold surfaces, is caused by air laden with moisture (humidity being the measure of that moisture content) coming in contact with a cold surface. The cooler the air is, the less moisture it can hold. When air cools, its humidity rises, and if the temperature reaches the dew point, the water condenses on the cold surface.

So to control condensation we can address it from 3 angles.

Eliminating Cold spots
Eliminating moisture
Lowering humidity

Eliminate the Cold Spots

Cold water pipes, toilet bowls and tanks, windows in winter, etc, are all cold surfaces on which water can condense.

Cold Water Pipes

Cold water pipes can be insulated. There are two types of pipe insulation out there. There is the foam type, which comes in 3 ft or longer tubes with a slit up the length. These are the easiest to install and work with. They do not let air through and provide the insulation protection to prevent humid air from coming in contact with the pipe. To install them, run your finger through the slit to open it, and slide it onto the pipe. When you come to bends or elbows, you will need to cut small wedge shaped notches on the inside of the bend to allow the insulation to make the bend with the pipe. The insulation comes in different diameters for the various sizes of copper tubing you will be covering, so measure and buy accordingly. I find it helps to cover the whole seam with duct tape to hold it shut and seal it. I also tape the joints of the insulation between each section. As an added measure, I push each section tightly together with the preceding one to keep the insulation together. I have noticed some shrink of the insulation after some time which otherwise would leave a gap.

The other type of insulation is a roll of fiberglass insulation with a roll of plastic to cover it. This is easier to use on bends and around valves etc., (though I still prefer the foam type) and is less expensive. You wrap the pipe with the insulation and then you wrap the insulation with the plastic vapor barrier. The vapor barrier does not provide as tight a seal and moist air can get in, eventually wetting the insulation reducing its effectiveness. That is one major reason for using the foam tupe type.


Windows will sweat in very cold weather. The better the window, the less likely it will sweat. Double pane windows provide a better insulated surface than single panes. Windows with storm windows will sweat less than those without. Windows with a thermal break or wooden frames will sweat less than aluminum frames. So the answer to windows that sweat is to replace older windows with newer more thermal ones, and/or add storm windows. Heavy insulating curtains can help by reducing the flow of humid air to the cold window, however, the window will be colder since it is behind the curtain and away from the room's heat and you may find the moisture freezes on the window.

You will find there is no way to prevent condensation on windows in high humidity conditions such as during and after a shower or while cooking. The use of exhaust fans in these areas to remove the high humidity air will be helpful for both this room and the rest of the house. The moisture in the bathroom or kitchen will spread to the whole house. Your kitchen and bathroom should have an exhaust fan vented to the outside and you should use it when you are creating a significant amount of moisture.

Toilet tanks

Generally more a problem in the humid summer than the drier winter, the cold water that fills your tank will cause the humid air in the bathroom to condense on the cold surface of the tank and bowl. The simplest fix for this is to cover the tank with one of those decorative tank covers. They insulate the tank keeping the cold surface away from the humid air. Unfortunately they don't always go all the way around. You can get new toilets with insulated tanks, or you can get an insulation kit for the tank. These kits add a layer of poly insulation to the inside of the tank to keep the outside surface from getting cold.

There are also mixing valves which you can install on the cold water line leading to the toilet. These valves tie a hot line to the cold line with a small thermally controlled valve. The valve lets in enough hot water to warm the cold water to prevent the tank from getting cold enough to condense water on the tank.

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Walls and ceilings.

You may get condensation on your walls or ceilings during very cold weather. Sometimes the only way you notice this is by the patch of black mold or mildew growing there. This condensation is invariably caused by inadequate insulation in that area. Sometimes there is a spot that was missed, or the insulation has settled or fallen away. If it is in a ceiling and you have access to the attic, it should be relatively easy to solve the problem. Find the affected area and ensure it gets re-covered by the insulation. If the problem is in a part of a wall, you will have to fill the gap with insulation through the wall. A small hole (or holes) can be drilled into the wall and insulation can be blown or sprayed in. Then the hole patched and repainted.

Eliminating the Moisture

In older homes with leaks in every window, door and fixture the humidity drops in the winter as the outside air temperature drops. Since the house is getting so many air changes from its many drafts, the cold air coming in, when warmed has a very low relative humidity. However in a new home, there is quite a different situation. New homes are sealed tight as a drum. This makes them much cheaper to heat and cool, but brings along the problem of higher humidity in winter. Breathing, cooking and bathing all add a significant amount of moisture to the air. Without those drafts carrying the moisture outside, the humidity in the house rises. This can cause problems in the walls and attic of the house as well as making it rain on even the best thermal windows. In the walls and attics, when the moist air makes its way through the insulation and reaches the cold, it condenses, reducing the insulation's effectiveness and can cause dry rot in the wood.


To eliminate the moisture, use those bathroom and kitchen fans during times when you are adding a lot of moisture to the air (as we said before). If you burn a kerosene heater unvented in your home, you will be adding a significant amount of moisture to the air. These should be vented to the outside if you have a moisture problem in your house.

To lower the humidity level, an air to air heat exchanger can be added to vent the house's air outside and bring in fresh air. By using the outgoing air to raise the temperature of the incoming air, they are somewhat more efficient than merely cracking a window and running your bathroom fan. They will bring in fresh air which is a healthy thing in itself.

Seal out the moisture

A significant source of humidity for many homes is a crawlspace with a dirt floor. These should always be covered from wall to wall with plastic. 6 mil poly plastic can be bought in very wide rolls and laid out on the dirt floor weight down around the edges. All the seams should be over lapped and even taped. Where the plasitc meets the wall, to make and even tighter seal, you can use roofing tar to seal the plastic to the wall. Just paint a strip all the way around the wall with the tar and stick the plastic to it. This vapor barrier will eliminate a great deal of moisture coming into the house.

Lowering Humidity


Even in a relatively dry house, often the basement can be damp and moisture can cause growth of mold and mildew.. and that dank smell it causes. If a basement is cooler than the rest of the house and the outside in the summer, than its relatively humidity will be much higher. Therefore a dehumidifier should be run in the basement at least until it is warmer in the basement than the air outside.

Use the chart below to determine what size dehumidifier you should use for your basement.

Dehumidification Guide

Just as an oh-by-the-way, a dehumidifier will add noticable heat to the room it is in. This is due to the fact that it is not dumping the heat from the compressor and the condensing coils outside like an air conditioner does. So, though the humidity is dropping the temperature will be rising.

Heating the room

The warmer a room is, the lower its relatively humidity, so if it is practical heating a room in winter will lower the humidity. This may be an appropriate fix for an unheated attic room.

Air Conditioners

Air conditioners in addition to cooling the air, drop the humidity by removing a significant amount of water from the air. During the hot air conditioning times of the summer, it is more economical and practical to NOT open the windows at night even if it cools outside slightly. Leave the house closed up and don't bring the humid air inside. If you do, during the day, the air conditioner will be working that much harder to remove the heat and moisture from the air that was introduced during the night. There is a significant amount of moisture not just in the air, but absorbed by the furniture, wood etc in the house that will need to be removed to lower the humidity level in the house again. For comfort, a humid room will have to be much cooler than a dry room to have the same degree of comfort feel. So, consider this when it cools off a bit outside, if you will be running the A/C again tomorrow and it is still humid outside, don't open the windows.

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