How to fix a wet, damp, or downright leaky basement

5 min read

Learn how to dry out your wet basement by diverting water runoff, fixing leaks, eliminating condensation, and covering damp floors.

Winters are long in Vermont, so it’s a relief when spring finally arrives. But snowmelt and rainfall can spell trouble for a basement: leaks, dampness, condensation, even standing water. Assuming you haven’t had a bona fide flood, there’s plenty you can do yourself to dry out your basement. Fixing the issue will also help you ready your home for energy efficiency upgrades like air sealing and insulation.

First, pinpoint the location and severity of the problem: is water everywhere or seeping in at just one corner? If it’s running water, is it a trickle or a rushing river? Next, identify the type of water issue you have. Most fall under one of three categories.

1. Runoff or surface water

Does your basement get wet only when you have a serious storm or snowmelt event? Then you’ve got a runoff problem, and the place to start is outside. If you fix the issue at the source, then there’s a good chance you won’t have to do much inside your basement.

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, then 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 or excavate a band (about 1 foot deep, 3–4 feet wide) right up 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. Once it’s in place, this solution is maintenance free.

2. Condensation

Two things cause condensation: cold surface temperatures and elevated air humidity. So to reduce it, you have to warm up your basement or dry out the air.

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: it may seem counter-intuitive on a hot August day, but you should keep basement windows closed. Opening them will increase the air’s humidity level. And we don’t recommend storing your winter firewood supply in the basement; unless the wood is seasoned to less than 20 percent moisture content, it will release stored water into the air.

3. Subsurface water

So far, we’ve covered ways to keep out surface runoff (rain, snowmelt) and reduce interior humidity and condensation. But if those don’t work and you still have water seeping in below grade, then you’ll have to deal with the water where it is—inside. In this scenario, solutions can get more complex and may require assistance from a pro.

French drains: sounds fancy, but it’s simply a slender trench resting right up against the inside of the foundation wall. When water gets in, it drops into the trench and is channeled to a covered sump pump or “drain to daylight.” A sump pump can work well, but needs regular monitoring to ensure it’s working properly. It may also 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.

What about insulation?

To fully realize the benefits of air sealing and insulating your home, we recommend you deal with any sources of moisture or water in your basement first. Once you’ve done that, applying foam insulation and sealing windows and cracks will make a huge difference in warming up and drying out your basement, which will also eliminate most condensation issues. In Vermont, foundations are typically made of fieldstone or concrete (either poured or blocks). Which type you have dictates what insulation material you or your contractor use.

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.

Can't I just run a dehumidifier?

Dehumidifiers can be effective at removing moisture, but they can’t fix underlying issues. They can also make for a high electric bill. Consider, too, that they don’t work as well at lower temperatures—so you can’t expect them to do much in a cold, damp winter basement. In the long run you’ll save energy and money by preventing water from getting into your basement in the first place. If you do buy a new dehumidifier, however, make it an ENERGY STAR® certified model and check the availability of a rebate.

The bottom line

Moisture and water in the basement can be a serious hazard to the health of a building and its occupants. So take care of it sooner rather than later. If you suspect you already have mold, here are some useful guidelines for dealing with mold.