Basements can be hard to keep dry. Heavy rainfall or burst pipes combined with poor drainage can flood a basement quickly, causing water damage. Since a basement or crawl space serves as a home’s foundation, flooding can ultimately cause structural damage that seriously affects the house’s stability. Below, we’ll explain how to waterproof a basement to prevent flooding and what to do if your basement has already flooded.

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Understanding the Causes of Basement Flooding

Before diving into prevention strategies, figure out what’s causing the problem. 

Common Sources of Water Intrusion

Basement flooding often results from various sources, including:

• Backed-up municipal sewer systems
• Burst or leaking pipes
• Cracks in the foundation walls or floor
• Heavy rainfall or rapid snowmelt
• Improperly sealed windows and doors
• Malfunctioning sump pumps
• Overflowing gutters and downspouts

The Role of Poor Drainage

In the absence of an obvious water source, inadequate drainage around a home’s exterior is a leading cause of basement flooding. When water accumulates near your foundation, it can seep through even the smallest cracks or porous concrete. This damage can in turn allow even more water indoors. Proper grading and a well-designed drainage system are crucial for directing water away from your home’s foundation.

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Preventing Basement Flooding

You can keep water out of your basement by carefully inspecting your home’s drainage system and fixing any problems before the next rainstorm. Here’s how to address common causes of basement water, from relatively quick and simple fixes to more complex renovations.

Clean Gutters and Downspouts

Gutters protect your basement by directing precipitation away from your foundation. If they’re clogged or leaky, they can’t do their job. Remove leaves, dirt, and other debris from your gutters at least once a year to ensure water flows freely. Install downspout extensions to direct water at least 4–6 feet away from your foundation. Alternatively, you can install rain barrels or a dry well to collect the water and use it for irrigation.

Seal Around Windows and Doors. 

Even if water isn’t pooling around your foundation, some can sneak in through penetrations in basement walls. Use caulk or expanding foam to close any gaps around basement windows and doors. If your basement has egress windows, ensure the window wells have functioning covers or drains.

Inspect Appliance Connections

Look for leaks in the drain pipes connected to washing machines and dishwashers. Consider smart water leak detectors for these appliances. These detectors typically consist of a float placed near the base of the appliance. If there’s enough water to lift the float, an alarm will sound. Some will even shut off the appliance automatically.

Monitor Your Water Meter

Check for hidden leaks by taking a meter reading and then not using water for a few hours. A change in the reading could indicate a leak, including those underground near the foundation.

Waterproof Basement Walls

Simple, do-it-yourself (DIY) waterproofing solutions will only stop minor seepage through concrete, but they’re often inexpensive and easy to apply. Seal unfinished basement walls with a layer of waterproofing paint, and use silicone caulk to plug small cracks in concrete. For more extensive interior waterproofing, you can install a vapor barrier, though you’ll need to hire a professional for best results.

Install an Indoor Drainage System 

If standing water regularly pools in the basement, you need to remove it. Often, this consists of installing a sump pump inside a pit beneath a floor drain. You may also need a series of French drains around the basement floor to collect water. Make sure the pump has a battery backup for power outages.

Install an Outdoor Drainage System

If water continues to pool near your foundation, a French drain, also called a drain tile system, is also a good fit for outdoor drainage. This perforated pipe, surrounded by gravel, will redirect water away from your home’s foundation.

Check Your Sewer Lines

Have a plumber inspect your home’s sewer biennially, especially if you have older pipes or trees nearby. Consider installing a backwater valve in case the city sewer system becomes overloaded.

Seal Foundation Cracks

Inspect your foundation regularly for cracks. You can fill small, vertical cracks with epoxy or hydraulic cement. Larger or horizontal cracks need professional attention, as they could be signs of serious damage.

Regrade Your Yard

Ensure the ground around your home slopes away from the foundation. You may be able to handle small regrading projects with a shovel, but larger projects will require heavy machinery or landscaping professionals. Additionally, consider planting shrubs and water-loving plants near downspouts to help absorb excess water.

Encapsulate Your Foundation

Wrapping your home’s entire crawl space, basement, or foundation in a waterproof membrane is a large, expensive job, but it provides a permanent solution to flooding. You’ll be protecting your home’s foundation from serious structural problems.

Check out the video below to learn more about ways to prevent your basement from flooding. Damage-prevention specialist Michael Millegan highlights different types of sump pumps and water leak detection systems, including water-powered sump pumps that continue working even during a power outage.

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Professional Waterproofing Solutions

While many preventive measures can be DIY projects, some situations require professional expertise to ensure long-term protection against basement flooding.

When To Call in the Experts

Consider consulting a professional waterproofing contractor if:

• You experience recurring basement flooding despite DIY efforts
• There are signs indicating significant structural damage to your foundation
• You live in an area with a high water table or frequent heavy rainfall
• You’re planning to finish your basement and want comprehensive protection

Choosing a Reliable Waterproofing Contractor

When selecting a waterproofing professional:

• Verify proper licensing, bonding, and insurance
• Check their Better Business Bureau rating and customer reviews
• Ask for detailed, written quotes and explanations of proposed solutions
• Get multiple estimates to compare prices and approaches

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Emergency Measures for Heavy Rain

When heavy rain is forecasted, taking quick action can help prevent or minimize basement flooding. Being prepared and having a plan in place can make a significant difference in protecting your home.

Installing Temporary Flood Barriers

Consider investing in temporary flood barriers that can be quickly deployed around your home’s perimeter. These barriers can help divert water away from your foundation during extreme weather events. Assess the potential entry points for water and position barriers accordingly to maximize their effectiveness.

Using Sandbags Effectively

Sandbags can be an effective temporary measure to protect your home from flooding. Place them around entry points and along the perimeter of your home to create a barrier against rising water. Remember to dispose of used sandbags properly after the threat has passed, as they may be contaminated with bacteria or mold from floodwater.

Reinforcing Vulnerable Areas

In addition to sandbags and barriers, reinforce vulnerable areas such as basement stairs and window wells. Consider using plastic sheeting or tarps to cover these areas and prevent water from seeping in. Regularly check these reinforcements during heavy rain to ensure they remain intact.

Staying Informed

Stay tuned to your local radio or TV station for updates. Know how your state, city, or municipality will communicate an evacuation order if it becomes necessary. Be aware of evacuation routes and shelter locations just in case.

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Dealing with a Flooded Basement

If your basement does flood, quick action is crucial to minimize damage and prevent health hazards. Check out our guide to flooded basement repair for more details, but here are the basic steps to take.

Immediate Steps After Flooding

Follow these steps if your basement floods:

1. Turn off your electricity and gas if it’s safe to do so.
2. Wear protective gear (rubber boots, gloves, face mask) before entering the flooded area.
3. Check for signs of structural damage like sagging ceilings or bowing walls.
4. If it’s safe to do so, open doors and windows and unplug appliances.
5. Call your insurance company and document the damage for insurance purposes
6. Remove standing water using pumps, wet vacuums, or buckets.

If the water level is more than a foot high, do not pump out more than 1 foot every 24 hours. The U.S. Environmental Protection Agency warns that removing the water too quickly can cause walls to crack or collapse.

Drying and Sanitizing Your Basement

After removing water, begin drying out the area as soon as possible, since the chance of mold growth increases sharply after 48 hours.

1. Take salvageable items outside to dry.
2. Keep windows and doors open to allow ventilation.
3. Use fans and dehumidifiers to dry the area thoroughly, aiming for a humidity level of 30%–60%.
4. If you have central air conditioning, run it to provide additional dehumidification.
5. Remove and dispose of wet carpeting, drywall, and insulation.
6. Clean and disinfect all hard surfaces to prevent mold growth
7. Monitor for signs of mold or mildew in the following weeks

If you see signs of mold, stop using fans. They may actually spread spores around.

Calling in the Professionals

In some cases, dealing with basement flooding is best left to professional abatement teams or sanitation workers. Here’s who to call and when to call them.

• Asbestos abatement specialist: Your home contains asbestos building materials (e.g., floor tiles) that were damaged in the flood.
• Electrician: Your home’s wiring has been compromised.
• General contractor: You need help coordinating multiple specialists for large repair jobs.
• Mold abatement specialist: Mold growth exceeds an area of about 10 square feet.
• Plumber: The problem is leaky or burst pipes, or your gas lines have been compromised.
• Structural engineer or foundation repair expert: You suspect your home has sustained structural damage.
• Water damage restoration expert: The floodwater source is sewage or a natural disaster, or the damage is more extensive than you can handle.
• Waterproofing specialist: You want to explore long-term preventative solutions, including exterior waterproofing and advanced drainage systems.

Anyone you hire should be properly licensed, bonded, and insured to carry out the work you need. All states require plumbers and electricians to have a special license. Other contractors, such as waterproofing and water damage experts, don’t typically need a specific license, but check with your state.

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Our Conclusion

Preventing basement flooding is all about sealing leaks and ensuring proper drainage so water flows away from your foundation. You can take many steps on your own, but if you live somewhere with a high water table or lots of precipitation, you may want to call in professionals. Basement waterproofing costs are often lower than repairing water damage or foundation repair prices.

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FAQ About Basement Flooding

What is the average cost of basement waterproofing?

Basement waterproofing costs $3–$10* per square foot depending on the method, so a 1,000-square-foot basement will cost $3,000–$10,000. Most homeowners pay between $2,457 and $8,173.

* Cost data sourced from contractor estimates used by Angi.

How do I know if my basement has water damage?

Here are some signs that your basement has a moisture problem:

• Foundation cracks
• Visible water stains on the walls, floors, or ceiling
• Bubbling, flaking, or peeling paint
• Damp or rotting wood
• Efflorescence (white mineral stain) on concrete floors or walls
• Mold or mildew
• Musty or stale odors
• Puddles or standing water

Should you let a flooded basement dry on its own?

No, you shouldn’t let a flooded basement dry on its own. Improper drying could lead to mold growth, weakened foundations, or other physical damage to your home. Remove excess water immediately and dry the area with humidifiers or fans.

Why does my basement flood during heavy rain?

Your basement floods during heavy rain because excess water that your yard can’t absorb puts pressure on your basement walls. The water then seeps inside through cracks or porous concrete. Downspouts that don’t extend far enough from your home, clogged gutters, and overflowing sewer systems can all contribute to basement flooding.

How do I keep rain water out of my basement?

To keep rainwater out of your basement, make sure your gutters and downspouts direct water several feet away from your foundation. Inspect your foundation for cracks and consider waterproofing it. Finally, make sure the ground slopes away from your home to encourage proper drainage.

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