Approach to Water Problem in Basements and Crawl Spaces

Wet basements and crawl spaces are sources of high humidity, which can produce surface condensation, mildew and fungi, musty odors, and an unhealthful environment. Such moisture can cause deterioration of floor joists, beams, subflooring, insulation, and electrical-mechanical systems. Prolonged water around the footer and foundation wall can soften the soil and weaken its bearing capacity, increasing the possibility of wall settlement and cracking. Serious seepage under the foundation footer may erode soil away and cause the wall to drop or crack.

Excessive moisture can eventually penetrate the subflooring and buckle the flooring or cause warping, making doors and cabinets difficult to close or open. Since crawl space or basement dampness always moves toward the drier upstairs areas, higher humidity will result in costlier heating and air conditioning bills. In the case of crawl spaces, if the underflooring insulation collects moisture, or sags from excessive wetness, the heating and air conditioning costs are driven even higher. Finally, wet basements and crawl spaces reduce the value of the house--at least by the amount that would be required to repair the damage and to eliminate the cause of the problem. Some homeowners are reluctant to discuss or admit their water problem, for fear that the publicity of an actual or even a perceived problem would reduce the value of their investment. Homeowners, in such situations, should immediately seek professional assistance in assessing the source and extent of the problem and in finding a remedy.

CAUSE OF WET BASEMENTS AND CRAWL SPACES

Most wet basements or crawl spaces are caused by surface water which is not adequately drained away from the foundation wall. Sources of this water include the following:

• Roof water if no guttering is present

• Roof water if the guttering leaks or overflows because of clogging from leaves and bird nests

• Roof water if the downspouts (leaders) are clogged or do not have sufficient means at their outlets to drain water away from the foundation wall. Frequently, a downspout ends at the corner of the house without a splash pad (splash block) or elbow (shoe), leaving roof water to concentrate at that point and seep into the soil next to the foundation wall. A typical 2000 square foot roof can produce almost 1250 gallons of water during just 1 inch of rainfall. If the rainfall is steady and prolonged, the opportunity for this roof water to soak into the ground next to the foundation wall is high.

• Excessive watering of flower beds and shrubbery around the foundation wall. Once the upper soil layer or mulch bed air spaces are filled with water, the excess water either runs off or seeps into the ground next to the wall. Prolonged and excessive watering can contribute a large amount of water to crawl spaces or basements.

• Rainwater runoff from the adjacent lawn, walks, or driveway areas if the landscaping forces water to drain toward the house instead of away. If surface runoff is directed toward the foundation wall, this water will pond and eventually soak into the soil, thus becoming a potential source of basement or crawl space water. Downspout splash pads are not very effective if they drain onto a backward-draining slope toward the foundation wall.

Water or dampness problems in basements or crawl spaces are sometimes caused by other factors:

• Subsurface or groundwater may be intercepted or dammed up by a basement or foundation wall. Houses which are built downslope on or at the base of hillsides are particularly vulnerable since there is greater opportunity for surface water to soak into the soil to become groundwater and because groundwater flows downhill by gravity. Foundation walls act like dams and can intercept and trap this subsurface water, causing pressure build-up on the outside and forcing water through joints and cracks in basement walls or seepage under the footer.

• Nearby springs may have been filled in or covered up by the developer. Unless the springs were properly drained away from the lot or subdivision, such water will eventually seep into the surrounding fill, become a pool of groundwater, and eventually force itself laterally and upwardly into basements and crawl spaces.

• Nearby creek(s) may overflow during storm runoff and either directly flood basement or crawl space areas, or contribute to the groundwater, which may become sufficiently high to cause seepage into the basement or crawl space area. Homeowners may not experience the effects of groundwater seepage or overflowing creeks for months or years after purchasing a house because of drought or infrequent out-of-bank flooding. However, when such conditions do occur, they may come suddenly without warning and cause serious problems after the warranty period has expired.

• Improperly installed, clogged, collapsed, or leaky drains may not allow downspout water or foundation wall water to escape. Perimeter, footer, or foundation drains are installed around the exterior of a house below the basement floor to intercept and dispose of subsurface water to eliminate groundwater build-up and seepage under the house. If these drains are improperly installed or become clogged with silt or roots, they will not operate as intended. Sometimes an otherwise good perimeter drain gets covered up at its end(s) during the final backfilling or landscaping stages of construction and the intercepted water has no place to go but to build up behind the foundation wall and eventually to seep into the basement or crawl space.

• Underground drains leading away from downspouts may not have sufficient slope to carry water away; may empty into the adjacent lawn and get covered with topsoil; may become crushed during landscaping or become pinched at their outlets; or may lead to an area which ponds and backs up water. The end result in all these cases is leakage or overflowing at the bottom of the downspout and water penetrating the foundation area.

PREVENTING AND REMEDYING WET BASEMENTS AND CRAWL SPACES

Generally, surface water drainage should be directed from all sides of the house and off the lot in a manner that will

• Minimize possibility of dampness in basements and crawl spaces
• Prevent standing or ponding water on the site
• Prevent soil erosion
• Adversely affect the supporting foundation soil behavior.

Walks, driveways, retaining walls and other landscape improvements should be constructed so as not to interfere with drainage. Walks should not be used as drainage channels.

Site grading plans should specify minimum slopes from the house (usually 2 to 5%), depending on location, type of soils, frost depth, and soil moisture, to ensure water drainage for some specified distance usually 6 to 25 feet away from supporting foundations. In cases where minimum slopes or distances cannot be attained, paved gutters or other drainage structures acceptable to the Building Inspector may need to be installed.

Maximum slopes are usually specified to prevent erosion or unstable banks around the house and yard.

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