Complete Guide to Attics and Basements: Projects: Getting Started: Dealing with Basement Moisture

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Common causes of basement moisture include improper grading around the foundation, inadequate or faulty gutter systems, humidity and condensation, cracks in foundation walls, leaky joints between structural elements, and poorly designed window wells. More extensive problems include large cracks in the foundation, damaged or missing drain tiles, a high water table, or the presence of underground streams. Often, a combination of factors is at fault.

Basement moisture can destroy your efforts to create functional living space. Over time, even small amounts of moisture can rot framing, turn wallboard to mush, and promote the growth of mold and mildew. Fortunately, most moisture problems can be resolved, but any measures you take must prove effective before you proceed with your project. Ensuring your basement will stay dry throughout the seasons may take a year or more, but considering the time and money involved, it’s worth the delay.

Basement moisture appears in two forms: condensation and seepage. Condensation comes from airborne water vapor that turns to water when it contacts cold surfaces. Vapor sources include humid outdoor air, poorly ventilated appliances, damp walls, and water released from concrete. Seepage is water that enters the basement by infiltrating cracks in the foundation or by leeching through masonry. Often caused by ineffective exterior drainage, seepage comes from rain or groundwater that collects around the foundation or from a rising water table.

If you have a vet basement, look for evidence of moisture problems. Typical signs include peeling paint, white residue on masonry, mildew stains, sweaty windows and pipes, rusted appliance feet, rotted wood near the floor, buckled floor tile, and strong mildew odor.

To test for condensation and seepage, lay a square of plastic or aluminum foil on the floor and another on an exterior foundation wall. Tape down all four sides of each. Check the squares after two days. If moisture has formed on top of a square, you probably have a condensation problem; moisture on the underside indicates seepage.

To reduce condensation, run a dehumidifier in the basement. Insulate cold-water pipes to prevent condensate drippage, and make sure your dryer and other appliances have vents running to the outside. Central A/C service in the basement can help reduce vapor during warm, humid months.

Crawlspaces can also promote condensation, as warm, moist air enters through vents and meets cooler interior air. Crawlspace ventilation is a source of ongoing debate, and there’s no universal method that applies to all climates. It’s best to ask the local building department for advice on this matter.

Solutions for preventing seepage range from simple do-it-yourself projects to expensive professional jobs requiring excavation and foundation work.

Since it’s often difficult to determine the source of seeping water, it makes sense to try some common cures before calling in professional help.

Begin by checking your yard’s grade. The first 6 ft. of ground around the foundation should slope away at a rate of 1” per foot and at least 3/4” per foot beyond that. Use a level, long board and tape measure to check the grade. Build up the ground around the foundation to improve drainage.

Next, inspect your downspouts and gutters. Give the gutters a thorough cleaning, and patch any holes. Make sure the gutters slope toward the downspouts at about 3/16” per foot. And most important, add downspout extensions and splash blocks to keep roof runoff at least 8 ft. away from the foundation.

Window wells also allow water into a basement. Covering them with removable plastic is the easiest way to keep them dry. If you prefer to leave wells uncovered, add a gravel layer and a drain to the bottom of the well. Clean the well regularly to remove moisture-heavy debris.

To further help stop seepage, patch cracks in the foundation walls and floors. Use waterproof masonry sealant for cracks under ¼" wide, and use hydraulic cement for larger cracks. Whole-wall interior coatings, such as masonry waterproofer, may also help reduce basement moisture. However, be aware that while sealing the foundation from the inside can help block occasional and light moisture, it will not solve serious moisture problems.

If these simple measures don’t correct your moisture problems, you must consider more extensive action. Serious water problems are typically handled by footing drains or sump systems. Footing drains are installed around the foundation’s perimeter, near the footing, and they drain out to a distant area of the yard. These usually work in conjunction with waterproof coatings on the foundation walls. Sump systems use an interior under-slab drain pipe to collect water in a pit, and water is sent outside by an electric sump pump.

Find out if your house has one of these systems in place. It may be that our footing drain pipes are clogged with silt or have been damaged by tree roots. If you have a sump pit in your basement floor but no pump or discharge pipe in place, you may need to install a pump and drain lines. (There may be regulations about where the sump pump drains.)

Installing a new drainage system is expensive and must be done properly. Adding a sump system involves breaking up the concrete floor along the basement’s perimeter, digging a trench, and laying a perforated drainpipe in a bed of gravel. After the sump pit is installed, the floor is patched with new concrete. Installing a footing drain is far more complicated. This involves digging out the foundation, installing gravel and drainpipe, and waterproofing the foundation walls. A footing drain is considered a last-resort measure.

Test for condensation and seepage by taping a square of aluminum foil to the floor and a wall. Moisture on top of the foil indicates condensation; moisture underneath reveals seepage.


Improve your gutter system and foundation grade to prevent rainwater and snow-melt from flooding your basement. Keep gutters clean and straight. Make sure there’s a down-spout for every 50 ft. of roof eave, and extend downspout piping 8 ft. from the foundation. Build up the grade around the foundation so that it carries water away from the house.

To help stop seepage from inside the basement, patch cracks in the foundation walls and floors. Use waterproof masonry sealant for cracks under ¼” wide, and use hydraulic cement for larger cracks. Whole-wall interior coatings, such as masonry water proofer, may also help reduce basement moisture. However, be aware that while sealing the foundation from the inside can help block occasional and light moisture, it will not solve serious moisture problems, regardless of the manufacturer’s claims.

If these simple measures don’t correct your moisture problems, you must consider more extensive action. Serious water problems are typically handled by footing drains or sump systems. Footing drains are installed around the foundation’s perimeter, near the footing, and they drain out to a distant area of the yard. These usually work in conjunction with water proof coatings on the foundation walls. Sump systems use an interior under-slab drain pipe to collect water in a pit. From there, the water is sent outside by an electric sump pump.

Find out if your house has one of these systems in place. It may be that your footing drain pipes are clogged with silt or have been damaged by tree roots. If you have a sump pit in your basement floor, but no pump or discharge pipe in place, you may need to install a pump and drain lines. (Be aware that there may be regulations about where the sump pump drains.)

Installing a new drainage system is expensive and must be done properly Adding a sump system involves breaking up the concrete floor along the basement’s perimeter, digging a trench, and laying a perforated drain pipe in a bed of gravel. After the sump pit is installed, the floor is patched with new concrete. Installing a footing drain is far more complicated. This involves digging out the foundation, installing gravel and drain pipe, and waterproofing the foundation walls. Thus, a footing drain is typically considered a last-resort measure.

Before you hire someone to install a drainage system, do some homework. Learn about the procedure the contractor has planned, and find out if it has been successful with other homes in your area. Check the contractor’s references, and don’t be afraid to get a second or third opinion before deciding.

Foundation drainage systems are designed to remove water that pools around footings. Footing drains collect water from outside the footing and carry it out to daylight. Sump systems collect water underneath the basement floor and divert it into a pit. As the pit fills, a sump pump sends the water outside. Landscape drains remove water near the surface.

Fill cracks in the foundation with masonry water proofer or hydraulic cement. This helps reduce minor seepage and prevents further cracking.

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Updated: Tuesday, April 21, 2015 0:39