Stopping Basement Moisture Infiltration

There is a drastic difference between handling a damp basement and one with an actual water problem. If your basement receives any visible amount of liquid water, either puddling or flowing, you must repair the problems that cause it.

When you get enough water to see puddles or trickling streams it is usually coming in through a crack or faulty seam in the concrete wall or foundation. Cracks or leaky seams can sometimes be fixed with hydraulic cement. But you also must look for the cause of so much water accumulation in the vicinity of your basement walls and floor. Most common is a missing eaves trough (gutter) or downspouts that are either missing or too short. Often the ground around a house settles, causing water to drain toward the house rather than away. Water must drain away from the house. This means that the soil surface should slope down, away from walls. If you have a sump pump, make sure it works. If your house was built without a sump pump but outside conditions have changed so that drainage is a problem, you’ll have to address it. Get expert advice on what should be done. For example, you may have to re-landscape or install a sump pump. Many of these fixes are within the skill set of an experienced DIYer.

Did you know?

1″ of rain on a 1/4-acre (10,900 sq. ft.) lot deposits almost 6,800 gallons of water.

½” of rain on a 40 x 30ft house with a 5 pitch roof is more than 400 gallons of water, or approximately 100 gallons per down spout.

A damp basement can also be caused by humidity in the air or by water vapor coming through the concrete. In some cases, both of these sources may be contributing to the dampness. Dampness can usually be remedied by indoor repairs or equipment. For example, below grade walls and floors can be sealed using a brush-on sealant. This will reduce vapor infiltration. Even so, it is still a good idea to check for all the outdoor problems mentioned above in order to minimize the infiltration water pressure on the indoor fixes.

Did you know?

Relative humidity is the amount of water vapor in the air compared to the most that could be in the air. If you have 50%RH (relative humidity) that means the air has ½ of the maximum water vapor that it could have. Colder air has less maximum water vapor capacity—so for the same air, as you cool it, the %RH goes up. This is one of the major reasons why a cool basement can feel damp.

Basements are often cooler than the rest of the house…though they share the same household air in a basement the air can become cooler. In cool basements household air has a higher relative humidity (RH) than in the rest of the house. When relative humidity gets above 60% mold can grow. For example, if your first floor is at 70°F and 52%RH and your basement temperature happens to be 67°F, the household air in the basement has a relative humidity of 60%. All it takes is a few days above 60%RH to begin to notice the damp, musty odor of mold growth.

After you have stopped any water leaks and minimized water vapor sources and vapor infiltration in your basement you will be able to tell whether or not you need a dehumidifier. However, in general, if you’ve got a basement, you should have a dehumidifier. The usual cooler temperatures in a basement are much more comfortable with 45 to 50%RH and that is hard to get without dehumidification. In a dry basement quality furnishings will last longer and the whole basement will feel fresher and more livable. Look for an Energy Star-rated, high quality dehumidifier with a drain hose attachment or an optional condensate pump if you don’t have a nearby floor drain.

Want to assess your indoor hygiene?