Wet or damp basements can occur in both old and new homes, and it's critical to address the problem quickly. Moisture in a basement can create mold and mildew, as well as ruin flooring and wall materials. Even worse, a wet basement wall can become a structural liability, which can make it difficult to sell your home.
The most common methods of preventing basement water problems are to waterproof the walls and add drainage features, such as drain tile and a sump pump to eliminate water that collects in the basement. These measures are best installed at the time of original construction. For an existing home, adding basement waterproofing and a drainage system can be very expensive because it requires extensive excavation and landscape repairs.
The good news is not all leaky basements require waterproofing or a new foundation drainage system. The source of the water often is on the outside of the home, above the ground, and easily remedied.
Here are some common causes for and solutions to a wet basement.
Check the Landscape Grade
When homes are constructed, the areas around the foundation are often backfilled with loose soil. And this backfill can settle more than the surrounding undisturbed soil. Over time, the backfill compresses, creating a slope (grade) that angles downward toward the foundation. These low spots near the foundation can cause water to drain toward the house and pool against the foundation, where it seeks entrance through cracks.
Walk around the entire house with a critical eye, making sure the grade (dirt or lawn) slopes away from your foundation and basement walls. The ground should slope away from the foundation with a vertical drop of about 8 inches for the first 2 feet of horizontal distance from the foundation wall. Regrading the soil around a foundation remedies the problem in many situations. This can involve trucking in substantial amounts of soil to reverse the direction of the slope.
Check the Slope of Patios and Walkways
Patios and walkways made of concrete or brick pavers might also contribute to the wet basement problem if they improperly slope toward the house. Correctly constructed paved surfaces should slope away from the foundation by a pitch of at least 1/4 inch per horizontal foot of distance.
Large patios are sometimes built with a slight funnel shape, so rain water flows toward the center and into a drain there. The drain sometimes is connected to an underground perforated drain pipe that leads out to the lawn, possibly with a pop-up relief valve. But it is not uncommon for improper construction or soil settling to cause a patio to develop a slope toward the foundation.
This can be a difficult problem to correct. Solid concrete slabs, if they are small enough, can sometimes be mud-jacked to change their pitch to slope away from the foundation. Brick paver patios and walkways can be disassembled for the base to be regraded to the proper slope and then reassembled.
It also might be possible to create a small curb or dam along the edge of the patio or walkway where it adjoins the house. This combined with good sealing of the paved surface, can help to direct water laterally away from the house rather than allowing it to drain downward along the side of the foundation wall.
Where such solutions are not practical, you can minimize the problem by making sure that the roofline above the patio is equipped with good roof gutters and downspouts that direct water away from the patio and foundation.
Check the Driveway Slope
Paved driveways that slope toward the house can also direct water against the foundation, where it drains downward and seeks entry into the basement. Driveway slabs sometimes develop sunken areas near roof gutter downspouts. And the large, flat surface of a driveway can carry a lot of water, so checking its drainage is important.
This problem is especially prevalent in neighborhoods where the lots are narrow and adjoining neighbors share a common driveway that touches both foundations. Each rainstorm will dump water from both roofs onto the driveway.
If your driveway is draining into your house, one solution might be to have a concrete contractor pour a small curb up against your house where the driveway abuts it. This way, the water will be directed against the curb and flow down the driveway and into the street, rather than against your foundation or basement wall.
Check Roof Downspout Discharge
The problem of improper drainage outside the home can be made much worse by an improper discharge of the roof gutter downspouts. Roof downspouts can add a literal flood of water to areas prone to drainage problems. A 1,500-square-foot roof will shed around 940 gallons of water in a 1-inch rainstorm. If you assume that water will flow out of an average of four downspouts, you might have as much as 235 gallons of water pouring out of one downspout.
Downspouts often dump water right at the base of the foundation. Or they might be constructed to channel water through a vertical drainpipe along the foundation wall to the footing drain system and sump pump. But the vast amounts of water flowing off a roof can easily overwhelm such systems.
The best solution here is to equip downspouts with long horizontal extensions that channel roof water away from the foundation and into an area of the yard where the water is absorbed or directed away from the house. Also, make sure the gutters are clean and flowing properly.
Check Your Neighbor's Runoff
Another common source of problems, especially with small lots where the houses are close together, is water being directed toward your house from a neighbor's property. This often results from poor landscape grading on the neighbor's property or a roofline, roof gutter system, or downspout extension that directs water toward your home. It's also fairly common for new construction on a neighboring property to cause water problems for adjoining homes because it changes the way the water had been draining.
Most neighbors will take measures to correct the problem if you diplomatically draw attention to the issue. If reluctant, they also can be legally compelled to fix the problem if they are in violation of area codes.
One solution for water runoff problems is called a French drain system. This is a landscape project in which a gravel-filled trench helps to direct water in the direction you want. When combined with landscape grading that directs water away from the foundation and toward the French drain, it is a very effective method. A French drain system installed on the property line between two closely adjoined houses can help relieve water problems for both homes. Friendly neighbors might even be willing to share the cost of installing such a system.