Basement Condensation & Basement Leakage
If you do not have obvious flows of water after each rain but have persistent dampness, your problem may be basement condensation rather than water leaking through the walls. If dampness seems to be a hot-weather problem, basement condensation is the likely culprit.
What Is Basement Condensation?
The warmer air is, the more moisture it can hold. Conversely, when air cools, it often has to release moisture. The dew on your lawn in the morning is moisture that was in the air until overnight temperatures dropped to the point where the air could not hold all of that moisture. The same thing happens when warm summer air that is loaded with moisture comes into contact with your glass of iced tea: the glass cools the air, causing the air to give up some moisture as water droplets on the outside of your glass. In your basement, condensation develops when you have relatively warm, moist air contacting the cool surface of the walls. As the walls cool the air, droplets form on the walls and you've got a damp basement.
If you think condensation might be the problem in your basement, there is a simple test. Securely tape a 10" x 10" piece of plastic wrap onto the basement wall in an area where you have noticed dampness, sealing the edges of the plastic wrap with the tape. Check on the plastic over the next few days. Eventually you will get moisture: if the moisture is on the wall side of the plastic, you've got a leak; if the moisture is on the room side of the plastic, you've got a condensation problem.
Basement Condensation Solutions
Condensation problems are usually easier to fix than leaks. Depending on the circumstances in your home, you have several lines of attack, all of which are designed to reduce the moisture in the air. Excess moisture commonly comes from clothes dryers, clothes lines, showers, cooking, and dew.
Sources of Basement Moisture
Concentrate on potential sources of basement moisture in or near the basement. If you have an indoor clothes line, consider moving it outdoors (at least in the warm summer months) or increasing air circulation (more on that later). Check your dryer to ensure that the exhaust vent doesn't leak and has an unobstructed path to the outdoors. If your dryer exhaust is equipped with an energy saving switch, allowing you to exhaust air indoors or out, ensure that yours is set to outdoors and see if it takes care of the problem.
While uncommon, basement moisture sometimes comes from plumbing leaks. As you are checking your basement, be on the lookout for signs of a plumbing problem. One place to check is the pipes in the ceiling directly under the kitchen sink. Another problem location is the drain line that removes water from the indoor part of your central air conditioner. Some new high- efficiency furnaces have a drain line as well. If these lines are clogged or broken, they can put out a surprising amount of water.
Basement Exhaust fans. If there is a basement shower that gets a lot of use, install a basement exhaust fan that draws the damp air out of the house. Should these measures fail to resolve the problem, and you are rather certain that your problem is basement condensation, check moisture sources in other parts of the house. In very well insulated houses, even small amounts of basement moisture can be problematic. The kitchen and every bath should be equipped with a working exhaust fan. Make sure household members use the fans! (If you have trouble getting cooperation on this front, have the bathroom fans hooked up to the light switch. Whenever the light goes on, so does the fan.)
Air circulation in Your Basement
If the condensationin your basement is quite modest, and there are not obvious sources of excess moisture, increasing air circulation may resolve the problem. Some basements don't have air-conditioning vents, but it is usually a simple matter to create a couple of vents. If you already have vents, make sure they are open.
If your basement is so packed with stuff that air can't circulate anyway, additional vents will have little effect. You should get rid of some junk and create air passages around and between things. You especially want air to be able to flow easily along walls. If you do not have a central fan or air conditioner, or if it doesn't seem to adequately stir the basement air, you might want to run a circulating fan in the basement for a few hours each day. While it won't remove much moisture, it helps distribute the moisture evenly and eliminate damp spots.
Insulating Your Basement
Another approach to the condensation problem is to reduce the extent to which moist air contacts cool surfaces where it can condense. With this approach, you insulate exposed duct work, pipes, and walls - anywhere that water tends to condense. If the moist air can't reach the cool surfaces, it won't release water as condensation.