10 tips for dealing with damp basements

Ask the Expert Home Improvement
The key to preventing mildew/mold is moisture control.
The key to preventing mildew/mold is moisture control. GChristo - Fotolia

Q. I have a condo with a basement that has two tiny windows and one underground normal-size window that is inconvenient to open because I have to remove a plastic pit cover outside. The basement doesn’t have a bulkhead. I had a little mildew that the dehumidifier eliminated. I use the dehumidifier only during the summer, but I am not really certain when to put it on or what setting to use. Also, I thought it would be helpful to open the windows even though it is really inconvenient, but would that be defeating the purpose of the dehumidifier because now it would be working on outside air?


A. Determine whether your basement has a moisture problem and solve that first. Is there water on the floor? Are the walls moist? Don’t forget about the exterior of your condo; make sure there are gutters and the land is properly graded — both can cause moisture issues in a basement.

The key to preventing mildew/mold is moisture control. Damp basements can be the result of many things, including a high water table, a plumbing leak, water seeping through the foundation walls, and high humidity. All of these factors can foster mold and/or mildew growth, but damp conditions can lead to wood rot and even worse, structural damage, as well as health problems.

I recommend using your dehumidifier all year round. I leave mine on all year; it is automatic, turning on when it senses moisture in the air. I have mine on a shelf above an old laundry sink. It drains directly into the sink, so I never have to worry about emptying the tank.


1. Check for and repair all plumbing leaks.

2. Seal any cracks in foundation walls, windows, and doors.

3. If you have a laundry hookup downstairs, make sure your dryer is vented to the outside. Check for holes in the hose and clean both regularly.

4. Basement bathroom showers should have vents to remove shower steam and moisture.

5. Dirt floors should be covered with a vapor barrier. Concrete floors are preferred.

6. Install gutters and ensure that the downspout directs water away from the foundation. Drain pipe extensions on the ground are helpful. Clean your gutters.

7. Regrade the ground around the house so it slopes down and away from the foundation. Remove plantings that prevent this.

8. Install a sump pump if you have a high water table. Make sure it is working properly.

9. Use a dehumidifier in the basement to reduce condensation on the walls.

10. Scrub mold off hard surfaces with detergent and water and dry completely. Absorbent or porous materials, such as ceiling tiles and carpet, may have to be thrown away if they become moldy. Mold can grow on or fill in the empty spaces and crevices of porous materials, so it can be difficult or impossible to remove completely. Spray a bleach solution on these areas. Ventilate the area before you do this.

Dear Rob

George in West Roxbury: I had a similar problem to the one you answered last week; my doors would close by themselves (“Ask the Carpenter: How to fix doors that are warped or won’t stay open,’’ April 16). I spent a lot of time thinking about a fix and tried a few, but they didn’t work. Then I purchased an inexpensive rare-earth magnet online. I screwed the round magnet to the bottom of the door and then added a spring (metal with rubber at the end) from a local hardware store to the base of the wall. Guess what? Problem solved.

Rob: Great tip. Thanks, George.

Rob Robillard is a general contractor, carpenter, editor of, and principal of a carpentry and renovation business. Send your questions to or tweet them to @robertrobillard. Subscribe to the Globe’s free real estate newsletter at