Wet and damp basements can be more than just uncomfortable. Unchecked moisture allows mold and fungi to flourish, which can cause allergic reactions in people and pets and can result in peeling paint; rotting wood; and warped drywall or other wall, floor, and ceiling components.

Sample of the simplified drainage system

With either a basement or slab foundation, in addition to applying a 1?2 inch of parging masonry (or cement) on the outside surface of basement walls, followed by two coats of a bituminous tar sealant, make sure good drainage is achieved around the entire dwelling. Grading or sloping the soil away from the home’s perimeter is essential to effectively controlling roof and outside wall water runoff. As a rule of thumb, the soil should slope downward at least 6 vertical inches in the first 10 horizontal feet of travel from the foundation wall or outer vertical surface of the slab.

Some of the best drainage systems direct water that comes near the foundation down toward the level of the home’s footing, where clay, concrete, or plastic drainage tiles or pipes collect and convey the water away from the dwelling, or collect and discharge the water through a sumppump. For drainage lines to work efficiently, they must be securely installed in beds of porous material — usually washed gravel. To achieve good drainage at window wells, the washed gravel should continue from the bottom of the wells to the foundation drainage tile. The window well should be wider than the window and frame and deep enough for at least two inches of washed gravel to be placed at the bottom of the well — while staying below the lower portion of the window’s frame. It’s important to prevent any chance of water getting up to any part of the window’s frame.

To address the “open” nature of window wells, galvanized steel window wells are available to hold back the earth, and sturdy grating should be fitted at the well’s top to prevent someone from stepping into the well. Plastic covers can also be placed over the top of window wells to keep out rain and snow.

Downspouts that carry rainwater away from roof gutters should be connected to a mostly horizontal (slightly sloped) length of pipe that carries the water several feet away from the foundation. If a sidewalk is in the way, drain tile can be used to run the water beneath the walk to open ground or a catch basin, depending on the landscaping serviced. If a downspout empties into a catch basin, then into a drain pipe, the catch basin should be positioned far enough away from the foundation so runoff during a heavy rain will not overshoot it and yet close enough to catch the slower flow during a light rain. The water can also be conveyed to a bubbler or “dry well” where the water is allowed to simply drain off or dissipate into the surrounding ground. Bubblers or dry wells should never be located within the drip line of large trees — where the soil could become saturated for long periods of time and could allow the tree to fall over (roots and all) in high winds.

On flat or level building sites where there’s no room for or possibility of establishing surface drainage slopes, a “trunk and arm” drainage system can help handle water runoff (see image). Such a drainage system consists of a perforated drain tile (usually 6-inch diameter), which acts as the trunk and runs parallel to the home’s foundation, and solid drain tiles (usually 4-inch diameter), which act as the arms, attached to the trunk with T connectors. The arm tiles run perpendicular to the trunk, spaced about 10 feet apart from each other and slope underground to dry wells filled with washed gravel, where the surface runoff water can collect and slowly dissipate into the surrounding earth.