Common Causes and Solutions for a Wet Basement

Flooded basement cleanup
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Wet or damp basements can occur in both old homes and new, although they are more prevalent in older homes for several reasons. Modern construction often includes features designed to prevent water from collecting in a basement or to remove it before it can cause serious damage, and these prevention and remediation features are often missing from older homes. Wherever basement water is an issue, though, it's critical that you address it. 

Moisture in a basement can create mold and mildew, and ruin flooring and wall materials. Moisture can make it impossible to use the basement space effectively as living space. Even worse, a wet basement wall can become a structural liability if not resolved, and it can make it difficult or impossible to sell your home. 

The most common methods of preventing basement water problems are to waterproof the walls and to add drainage features such as drain tile and a sump pump to eliminate water that collects in the basement. These measures are best added at the time of original construction when they are relatively easy and inexpensive to install. For an existing home, adding basement waterproofing and a drainage system is very expensive because it requires extensive excavation and landscape repairs.

The good news is that not all wet or leaky basements require adding waterproofing or new foundation drainage systems as a solution. Very often, the source of wet basement walls or a leaky basement is on the outside of the home, above the ground, and easily remedied. You may find that improper roof drainage, improper ground slope, or even your neighbor's drainage may be causing your problem.

Basement Waterproofing Isn't Always the Solution

Standard methods of waterproofing basement walls are only effective to a degree. The force of gravity causes water to flow downhill, and if your property includes a driveway, patio, or lawn that is sloped toward the house, it means that water will flow downward until it encounters your home's foundation wall. Your basement wall now functions as a dam, causing a reservoir of wet earth and pressure to build up against your basement wall. The pressure can push the water into your wall and through the smallest crack. Worse yet, the pressure creates its own cracks in the wall. It is also possible for ground water to flow under the foundation and concrete floor slab, where it can rise up through the floor itself. 

The more water produced by a rainstorm or other sources, the worse your problem. It can become severe enough to cause structural failure from the pressure against the foundation wall or from the erosion of the subgrade upon which the foundation rests. At that point, whole sections of your basement wall may crack and fall away, requiring very expensive foundation underpinning. This is why during widespread regional flooding in disaster situations, the official recommendation is sometimes to fill the entire basement with water to equalize the pressure on both sides of the wall to prevent collapse

Fortunately, such disastrous situations are rare. More commonly, it is an uncharacteristic heavy rain or frequent rains that causes basement water problems, and it is this type of situation that basement waterproofing measures and foundation drainage systems are designed to prevent. But neither measure addresses some of the common causes of water problems, nor will they prevent water from entering your basement if rainfall is especially intense. 

You can however, take a number of common-sense measures that keep waterproofing and drainage systems from being overwhelmed. 

Flooded basement
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Check the Landscape Grade


When homes are constructed, the areas around the foundation are often backfilled with loose soil, and this backfill may settle more than the surrounding undisturbed soils. Over time, the backfill compresses, creating a slope (grade) that angles downward toward the foundation. These low spots near the foundation cause water to drain toward the house and pool against the foundation, where it flows down along the wall, seeking entrance through cracks and creating dangerous pressure. 


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 24 inches of horizontal distance from the foundation wall. Regrading the soil around a foundation remedies the problem in many situations. This may involve trucking in substantial amounts of soil to reverse the direction of the slope immediately around the foundation wall. 

Fixing the grade around the foundation so it slopes away can be one of the most successful methods of eliminating basement water problems, especially when combined with proper roof gutters, downspouts, and extensions to channel rainwater away from the foundation. 

Historic Hudson residential architecture
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Check the Slope of Patios and Walkways


Patios and walkways made of concrete or brick pavers may also contribute to the wet basement problem if they improperly slope toward the house. Properly 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 that rain water flows toward the center and into a drainage pit in the center. The drainage pit 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 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 so they slope away from the foundation. Brick paver patios and walkways can be disassembled so the base can be regraded to provide the proper slope, then reassembled. 

It may 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, may help 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 well away from the patio and foundation. 

Small garden designed around house with decking and patio pots. designer anthony paul. summer. ref: 1312158
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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. 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, then one solution may be to have a concrete contractor pour a small curb up against your house where the driveway abuts it. This way, the water is directed against the curb and flows down the driveway and into the street, rather than against your foundation or basement wall.

Cracked asphalt driveway with car parked
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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 1500-square-foot roof will shed about 940 gallons of water in a 1-inch rainstorm. Assume that water flows out of an average of four downspouts, you may have as much as 235 gallons of water pouring out of one downspout!

Surprisingly often, downspouts simply dump water right at the base of the foundation. Or, they may be constructed to channel water through a vertical drainpipe along the foundation wall to the footing drain system and sump pump. 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 well away from the foundation 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.

Drainpipe at a stone house
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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. Common causes are poor landscape grading on the neighbor's property, or a roofline or roof gutter system that directs water toward your home. It is fairly common, for example, for new construction on a neighbor's property to cause water problems for adjoining homes. If your basement water problems begin after a neighbor's construction project, the first place to look is at how their land is graded or the structure of their roof drainage system. 


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. Make sure your neighbor does not have a downspout extension dumping water onto your property, finding its way across your driveway and draining into your house. 

One effective solution for water runoff problems is called a French drain system. This is a landscape project in which a gravel-filled trench helps 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 may be able to share the costs of such a system. 

Eavestrough roof gutter downspout
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