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How to fix a wet, damp, or leaky basement
Learn how to dry out your wet basement by diverting water runoff, fixing leaks, eliminating condensation, and covering damp floors.
Snowmelt and rainfall can spell trouble for a basement. But assuming you haven’t had a bona fide flood, there’s plenty you can do yourself to mitigate leaks, dampness, condensation, even standing water. Fixing the issue will also help you ready your home for energy efficiency upgrades like air sealing and insulation. First, identify the type of water issue you have. Most fall under one of the following three categories.
Gutters: these can make a big difference for some houses, but they have to be maintained and can sometimes suffer damage from ice or snow. If you have gutters, clean them regularly and be sure the downspouts lead well away from the building.
Grading: if water tends to pool against your foundation, consider having a landscaper increase the slope of the grade away from your house. If you don’t have enough space to do this (for example, if you’re too close to your neighbor’s house), the next measure can be just as effective.
Underground “overhang”: dig out a band (about 1 foot deep, 3–4 feet wide) against the length of your foundation. Slope the band away from the house, place a membrane such as poly sheeting against the house and over the band, then backfill with stone or another material.
Cold water pipes: especially in summer, this is a classic location for excess basement condensation. If you take the time to wrap cold water pipes with foam pipe insulation, most if not all of the condensation will go away.
Dryer vents: if you have a clothes dryer in your basement, it must be vented to the exterior of the building. Check vent pipes for leaks or clogs, as these can contribute significant levels of unwanted indoor moisture.
Windows and wood: keep basement windows closed, especially in humid weather. And don’t store your winter firewood supply in the basement unless you've seasoned it to less than 20 percent moisture content.
French drains: sounds fancy, but it’s simply a trench resting right up against the inside of the foundation wall. When water gets in, it's channeled to a covered sump pump or “drain to daylight.” A sump pump needs monitoring to ensure it’s working properly, and may increase your monthly electric bill.
Cover your floors: in conjunction with a French drain, it often makes sense to install a high-grade vapor barrier over the entire floor. This barrier covers the French drain and sump pump, and runs right up the exterior wall to a point above where the water comes in.
Crawlspaces: even if your main basement floor is concrete, you might have a dirt crawlspace under a portion of your house. Don’t ignore it, because this may well be where moisture is getting in. To fix, try covering the ground with thick poly sheeting, overlapping and taping the seams.
Fieldstone foundation: irregular fieldstone surfaces are treated with spray foam insulation, which requires professional installation. Because most of the basement’s heat loss is at the top of the wall, your installer will want to cover at least the first couple of feet below grade. The more you can cover, the more energy efficient your house will be.
Concrete blocks and poured concrete: you can use spray foam on these foundation types, too. Or you can install sheets of rigid foam insulation, since the application surfaces are flat. Foam sheets cost less than spray foam and can be a DIY install job, depending on your skill and comfort level.
Important to know: any foam insulation you use, whether spray foam or sheets, requires a fire-protective paint coating or other approved covering according to safety code. And regardless of material, it’s essential that the insulation be continuous (no breaks or gaps) and cover the band joist all the way up to the underside of the subfloor.