Basement Flooding: Causes, Prevention, and Cleaning

Once you determine why your basement flooded, you need to prevent it from happening again. Landscape grading, foundation waterproofing, plumbing, drains, and sewers could be causing the problem and need to be repaired.

basement flooding

From overland flooding to poor drainage to sewer backup and broken pipes, basement floods have many causes. And there are many ways to prevent them.

Causes of Basement Flooding

Your basement is the lowest part of your house. Water flows downhill and can enter through cracks in the basement wall, under windows, or doors.

Wet Weather Basement Flooding

Wet-weather flooding is the main reason for basement flooding.

  • Overland Flooding. Heavy rains, fast snowmelt, streams, and water-filled ditches can cause flooding.
  • Foundation Drainage. Weeping tile and sump pump(s) are designed to move water away from the basement. If they fail to perform, you have a greater chance of basement flooding.
  • Seepage. Built-up water can seep through holes and cracks in foundations.
  • Sewer Backup. Heavy rains can fill up the entire sewer system forcing water back into house drainage pipes and into the basement.

Note: A sewer backup valve in your main sewer line prevents water and “stuff” from coming back into your house (usually the basement). The International Plumbing Code requires a sewer backup valve in new homes.

You can install a sewer backup valve in existing sewer lines. It will cost between $2000 and $5000, which is still less expensive than sewage sloshing around in your basement.

Dry Weather Basement Flooding

Sometimes, basement flooding isn’t caused by weather. For example, if the weather has been mild in your area, your basement flooding can be due to blocked sewer lines, broken pipes, leaky hot water tanks, or foundation issues.

  • Sewer Lines. Blocked or failed sewer lines, tree roots, collapsed lines, and flushing inappropriate items are all basement flooding causes.
  • Broken Plumbing Pipes. Water from broken pipes or overflowing toilets, tubs, or sinks will end up in the basement.
  • Foundation Drainage. Weeping tile and sump pump failure in houses built in low areas will allow water into your basement. 
  • Hot Water Tanks. Hot water tanks are well known for developing leaks.

Note: A working floor drain will keep damage to a minimum. If your basement has one, make sure it is not blocked off.

Preventing Basement Flooding

Acts of God and Mother Nature are difficult to control. Some precautions can reduce the chance and severity of basement flooding. For more detailed information, please see our article, Basement Waterproofing.

Keeping the Water Out

  • Landscaping. Ensure the 10’ wide band of soil beside the house is sloped away at least half an inch per foot.
  • Downspouts. Extend downspout run-offs to 10’ from the house.
  • Window Wells. Seal windows and install covers on window wells.
  • Exterior Waterproofing. Remove soil from around the house, seal the exterior of the foundation, and backfill. Then, ensure proper slope.
  • Interior Waterproofing. Seal the interior of the foundation wall with hydraulic cement or waterproof paint. Make sure your interior drainage system and sump pump are in working order. 

After the Flood

Cleaning up after the flood can be time-consuming, depending on the severity. Here are the steps you need to ake.

Turn off the Power

Turn the power off to the basement. If that’s not possible, call the power company and ask them to turn off the power from the outside.

You need to turn off the power to work in the basement safely. But you also need power for wet/dry vacs, fans, heaters, and power equipment. So get the power turned off in the basement and run extension cords from the main floor.

Determine the source of your Basement Flooding

Unless it is–or has been–torrential rain, sewer backup, broken pipes, or a sump pump malfunction are the most likely basement flooding causes. Of course, it could be another problem but start by looking for the most obvious.

If you are unsure where the water is coming from, turn off the main incoming line. Stop the water from coming in first, then start cleaning up and fixing leaks.

  • Sewer Backup. A sewer backup will appear at the floor drain or toilet. You may be able to solve the problem with a plunger or a plumbing snake. But you may need a plumber if an external sewer pipe is crushed or has tree roots in it.
  • Broken Intake Pipes. Pipes wear out when they get old and brittle and break or get punctured by construction. As a result, they can leak inside walls before it becomes obvious.
  • Sump Pump. Ensure the pump is working properly and the pipes are clear.

If none of these is the problem, continue searching. Water may be seeping through the walls or floor.

Cleaning up Flooded Basements

After the power is off and you have stopped the water from coming in, or the rain has quit, the real fun starts—here’s how to clean up a flooded basement: step by step.

  • Wear Protection. Flood water of any type can contain toxic contaminants. Wear waterproof boots, gloves, protective clothing, and an N95 mask or respirator. Goggles are a good option if you suspect mold.
  • Remove the Water. Use a combination of buckets and mops, a pump, and a wet/dry vacuum cleaner to remove the water as quickly as possible.
  • Remove Wet Items. Remove carpets, furniture, MDF molding, electrical cords, laminate flooring, and anything wet. Move it outside to dry in the sun. (Sunlight destroys mold.) Drywall and fiberglass batts readily absorb water and grow mold. Remove and dispose of the bottom foot of drywall and insulation after a flood. NEMA (National Electrical Manufacturers Association) recommends the disposal of anything with electrical wiring exposed to flood water.
  • Dry the Basement. 20” box fans move over 2000 cubic feet of air per minute (CFM). Get two going in the basement and open the windows. A basement dehumidifier will help to remove humid air–speeding up the drying process.
  • Cleaning and Kill Mold. Clean every part of the basement that was wet. Use bleach or Microban to eliminate any mold.
  • Replace. Replace everything you removed. Start with insulation and drywall and finish with furnishings.

Note: These suggestions work best for short-term flooding with less than 2 inches of water. For more severe flooding–longer and deeper–you will likely have to deal with drywall and insulation replacement, MDF trim replacement, and mold remediation.

Call a Professional Fire, Flood, and Restoration Company

You may not have any interest in–or the time to–clean out the basement. Or make the repairs. Your insurance company may not want you to be involved, either. Call good flood, fire, and restoration companies for quotes.

Many insurance companies have a list of services and people they have worked with before and have faith in.