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What Is the Best Way to Waterproof a Basement?

Last updated October 26, 2026

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The short answer

Start with the Outside

Waterproofing a basement begins outside your home. Check that the ground slopes away from the foundation so rainwater does not pool against the walls. A slope of about six inches over ten feet is a good target. Also, keep gutters and downspouts clear and extend downspouts at least a few feet from the house.

If your basement leaks after these basic fixes, the next step is often a drainage system. A French drain or a footing drain can collect water before it reaches your walls and move it away. This work usually requires digging around the foundation, so it is best done by the pros. Exterior drainage matters, especially in areas with heavy spring rain.

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Grading: ensure soil slopes away from the foundation.

Seal Interior Walls

Interior waterproofing products, like masonry sealants and waterproof coatings, can stop minor dampness and efflorescence. They work best on walls that are not under constant water pressure. Apply them to clean, dry surfaces, and follow the manufacturer's instructions carefully.

These sealants are not a cure for major leaks. If water is pushing through cracks or the floor, a coating will peel or blister. For active leaks, you need to address the source outside or install a sump pump and interior drain system. That is a job for the pros.

Masonry sealant: good for hairline cracks and damp walls.

Waterproof paint: helps with humidity but not hydrostatic pressure.

Crack injection: epoxy or polyurethane for active cracks.

Dehumidifier: reduces moisture in the air, not the source.

Install a Sump Pump

A sump pump collects groundwater that enters a sump pit and pumps it out of the basement. This is one of the most effective ways to keep a basement dry, especially in areas with high water tables. You can install a sump pump yourself if you are handy, but it requires digging a pit and connecting a discharge pipe.

If you choose to hire the pros, they can size the pump correctly and make sure the discharge goes far from the foundation. A backup battery or water-powered pump is wise during power outages. A backup helps prevent flooding when storms knock out electricity.

Sump pit: dig a hole at the lowest point of the basement floor.

Pump type: choose a submersible or pedestal model.

Consider a Drainage System

If water seeps through the floor or walls, an interior French drain might be the answer. This involves cutting a channel along the basement perimeter, laying a perforated pipe, and covering it with gravel. The pipe carries water to a sump pit, where the pump removes it.

This system handles water that comes from below or through the wall-floor joint. It is a significant project, and the pros often do it in a day or two. Make sure the pros seal the cut edges to keep out radon and soil gases.

Perimeter channel: cuts along the walls to catch water.

Perforated pipe: collects water and directs it to the sump.

Gravel: allows water to flow freely to the pipe.

Fix Cracks and Gaps

Cracks in basement walls or floors can let in water. Small cracks, less than 1/8 inch, can be filled with hydraulic cement or masonry patching compound. For larger cracks or those that are actively leaking, you may need epoxy injection or a professional evaluation.

Also, check the seal where the wall meets the floor and around pipes or wires entering the basement. Use caulk or foam to seal these gaps. If you see signs of water damage, like stains or peeling paint, address the source before sealing.

Hydraulic cement: expands to fill cracks and stop water.

Epoxy injection: for structural cracks that may move.

Caulk: seal around pipes and cables.

Foam sealant: fills larger gaps in the foundation.

Manage Humidity

Even with no visible leaks, basements can feel damp. Humidity can cause mildew and musty odors. A dehumidifier can help keep relative humidity below 50 percent. Run it continuously during humid months, and empty or drain it regularly.

Also, consider a vapor barrier on the floor if you have a crawl space or unfinished basement. This plastic sheeting blocks moisture from the ground. If you notice mold, see a doctor if you feel unwell, and call a mold professional for assessment.

Dehumidifier: set it to 45 to 50 percent humidity.

Vapor barrier: lay plastic over dirt floors.

Ventilation: open windows on dry days.

Air conditioner: helps remove moisture in summer.

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Frequently asked questions

Can I waterproof my basement from the inside only?

Interior sealants and coatings can handle minor dampness, but they do not stop water under pressure. For most basements, you need to fix drainage outside or install a sump pump and interior drain. Start with exterior grading and gutters before considering interior products.

How much does basement waterproofing cost?

Costs vary widely, from a few hundred dollars for sealants to several thousand for a full drainage system. The final price depends on the size of your basement, the type of waterproofing, and the extent of the problem. Get advice from the pros to understand your options.

Will my insurance cover basement flooding?

Policies vary, and your insurer decides what is covered. Flooding from storms or groundwater is often not covered by standard home policies. Sewer backup coverage may be an add-on. Check your policy and ask your insurance agent about specific scenarios.

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