What Causes a Basement to Flood?

Marwa Hasan
Written by Marwa Hasan
Updated January 31, 2022
construction worker waterproofing the foundation of a house
Photo: kuchina / Adobe Stock

If you don’t want to convert your basement into a swimming pool, the first step is knowing why it’s flooding

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If you have a frequently flooding basement it's not just water damage you need to worry about—basement flooding can cause mold, mildew, and other health hazards. But if you identify the causes of flooding, you can prevent water damage, save your property, eliminate the risk, and keep your basement dry. 

Here are eight of the most common causes of a flooded basement.

1. Your House’s Location

If you come home to find a small pond in your basement, your house’s location could be the culprit. Location is one of the most common reasons you have a flooded basement, especially if you live in one of the following areas:

  • Flooding-prone area: You live near a river or a stream that rises frequently

  • Low grading lot: If your house sits on a low point, the yard’s slope may promote water flow toward the house, not away

  • Bottom of the hill: Water will gather from surrounding hills—and end up in your basement

2. Poor Weatherproofing

Areas with frequent heavy downpours, hurricanes, or large amounts of melting snow tend to accumulate groundwater. This water rises to the level of your basement and seeps into hairline cracks—or connections of poorly sealed walls and floors—leading to a flooded basement.

During a home’s construction, walls, floors, and foundations must be waterproofed with a sealant to avoid water leakage and flooding. But over time, sealants deteriorate and leaks can sneak through the cracks. If your basement floods during most rainstorms, this might be a good time for a waterproofing upgrade.

To ensure a dry basement, you have to properly install a basement waterproofing system with a sump pump and proper drainage. You can hire a local waterproofing pro, or learn how to waterproof your basement yourself. Waterproofing can even improve your home’s return on investment!

3. Improper Drainage System

The weeping tile (or drain tile) is a draining pipe used for underground water collection. It’s built under the basement floor level around the building to ensure water moves away and doesn’t seep into your home.

If weeping tile fails or degrades over time, the basement may experience flooding, especially without proper waterproofing.

4. Clogged Gutter

A gutter is essential in draining rainwater. But if your gutters are near a tree, they tend to become jammed with fallen leaves, sticks, or other debris. This prevents water from draining safely from the roof, through the downspout, and away from your home.

Overflowing gutters can cause water to fall down the sides of your home, where it can pool and leak into the basement, causing foundation damage or wood rot.

A frequent gutter cleaning (at least a few times a year) will prevent water from collecting on your roof. Installing gutter guards will also lower the chances of clogs.

a hand with red gloves applies waterproofing tape to bottom corner of room
Photo: aleksandar29 / Adobe Stock

5. Downspouts Failure

Downspouts carry water from the gutter and direct it away from the home and foundation. But if the downspout is broken or positioned too close to the wall, it can actually drain rainwater toward the basement and overload the weeping tile. This can cause basement flooding, especially if you don’t have a waterproofing safety net.

To prevent flooding in the basement, downspouts should drain at least 5 to 6 feet away from the wall. Be sure to extend the downspouts with one of the outdoor drainage systems, which will help you discharge water at an appropriate distance away from your home.

6. Plumbing Leaks

Even if your home isn’t in a flooding zone, some plumbing emergencies could still cause flooding in the basement, including:

  • A burst pipe, a leaking waste line, or a clogged fixture

  • Blockage of a sanitary sewer due to flushing waste or pipe breaks

  • The sewer system can sometimes get overwhelmed with water, causing it to back up into your home through toilets, sinks, or floor drains

If you have a plumbing leak, you will see a large amount of water quickly—this is how you can tell it’s not a foundation seepage, which usually takes time to enter the basement. You’ll also notice that the water is dirty and smelly if the leaking is from a sewer backup or clogged drains. 

Plumbing flooding is a serious problem for homeowners and can be a health hazard. If this ever happens to you, call a local plumber to get it fixed ASAP.

7. Supply Line Leakage

A break in the water supply line and hot-water tank failure are both common reasons for flooding the basement. The most severe water leaking occurs during the winter months. That is when water freezes and expands, ultimately bursting the pipes, which sometimes causes basement flooding.

8. Broken Sump Pump

A sump pump is a draining device that keeps your basement dry and clear from groundwater. It collects excess water from the foundation or rainfall and drains it outside of your home. Regular inspection, cleaning, and testing the sump pump will ensure it's working properly and help you avoid a flooded basement.

The sump pump only works when there is power. If it loses power during a storm, it fails and shuts off, leading groundwater to enter the basement through the sump basin and flood.

What You Should Do If Your Basement Floods

Don’t forget to call your insurance after water damage to discuss what your homeowner’s policy covers. It might cover living expenses if you need to relocate during flood remediation. If you notice a plumbing leak, call a plumber immediately—If a burst pipe is causing the flooding, go ahead and shut off the water.

Follow the proper steps to clean a flooded basement safely, and avoid electrical hazards. Do not touch electrical items until they are completely dried. Wait for flooding to stop before cleaning up the water.

Shut off the power and gas and put on protective gear, including knee-high boots, rubber gloves, pants, a long-sleeve shirt, and a mask. Remove water with a wet vacuum, sump pump, or mop and bucket.

Move wet objects and furniture into a well-ventilated area to dry. Remove any parts of walls with water damage (cut out drywall), clean and dry every surface, and dispose of carpets and rugs. Use a dehumidifier to help everything dry faster.

Cleaning after a flood can be dangerous, and any missed water can lead to mold. Call a water clean-up and removal pro near you if you prefer to let a pro handle it. 

How Can You Reduce Risk of Basement Flooding?

Ideally, it’s best to prevent basement flooding before it happens. To reduce the chances of water seeping into your basement, you can take the following steps.

  • Seal any cracks in the walls and floors in your basement to keep it dry. Consider installing a basement waterproofing system like a french drain, window well drain, or sump pump. A pro can let you know which system is best for your home. 

  • Invest in a backup drainage system like a battery-powered sump pump to have on hand. These backup systems can power on if your main sump pump ever reaches its limit. 

  • Keep your gutters clean, and check the sides of your home for pooling water. 

  • Clean your downspouts regularly, and make sure all downspouts drain 5 to 6 feet away from your exterior walls. You can use downspout extensions if they’re too short. 

  • Reduce the risk for electrical hazards by relocating electrical appliances like washing machines away from flood-prone areas in your basement. 

  • If you experience heavy rainfalls, avoid using water during storms—don’t run the dishwasher or washing machine, and don’t take a shower or bath until the storm subsides.

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