How to Waterproof a Basement Interior and How Much It Will Cost

Waterproofing your unfinished basement is good for the health of your home and for you. Learn how to identify the cause of a wet basement and the best way to fix it.

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Waterproofing the basement is crucial to keeping your home in good shape, not to mention the personal health benefits it provides. Controlling moisture can prevent structural damage, lower utility bills, improve air quality and can even increase your living area by making a finished basement a possibility.

Thin coat of concrete applied on a floor.

Covering Asbestos Floor Tiles with Concrete

Foundation coatings are one way to control basement moisture, but they are most effective when used in conjunction with a drainage system and sump pump.

Photo by: Shutterstock


Foundation coatings are one way to control basement moisture, but they are most effective when used in conjunction with a drainage system and sump pump.

There is no better time than now to love on that lower level! The Inflation Reduction Act of 2022 provides homeowners up to $3,200 off their income tax bills for home upgrades that improve energy efficiency. That includes projects we discuss in this article, so save those receipts.

Basement moisture originates from outside and inside the home and can be present as liquid water and water vapor (humidity). A basement waterproofing strategy must be tailored to the individual home’s construction and climate but always comes down to two goals: preventing the moisture we can and managing the inevitable. Prevention involves sealing strategies and monitoring. Management takes the form of a bespoke recipe of drains, pumps and air manipulators.

How to Identify + Fix Foundation Seepage

According to, most of our unwanted basement water comes through our foundation. This is because foundation floors and walls are made of porous materials and, under the right conditions, the moisture in the soil outside migrates into the drier areas inside. Those right conditions could be a chronic state of your home being too close to the water table or an occasional problem of saturated ground.

Identifying the Problem

Standing water without a plumbing leak is a surefire giveaway, but damp walls could require a bit of investigation. This is because interior humidity sources can create the same look as exterior moisture coming through the walls.

  • Do the Foil Test: To know where wall moisture is coming from, do the foil test. Dry a test area of wall with a portable fan or heater. Take a 12-inch-square piece of aluminum foil or plastic and tape all sides to the wall to form a seal. Wait 24 hours. When you remove the test sheet, outside moisture will be on the side against the wall. Moisture on the outer side is from inside the home.


There are two ways to combat basement foundation seepage on the interior: apply coatings and install drains with sump pumps. In many cases, you'll do both.

A foundation coating makes a space more inviting and easier to clean, including from interior water leaks. What a coating will not do is be a permanent — or solitary — solution to foundation water problems. The most successful use of interior foundation coatings is in conjunction with a drain system and sump pump, which is what building scientists writing for the University of Minnesota Extension (UME) recommend.

There are a few interior drainage systems available, but all involve a perimeter channel that routes water to a collecting drain and onto a pit with an air-sealed sump pump.

Interior Basement Drainage Systems

Learn about the different systems that can waterproof your basement including French drains and sump pumps.

Applying a Foundation Coating

Pretty much any paint with a high percentage of solids will slow down moisture migration, according to Foundation-specific coatings are sealers, paints and more.

Buying Tips

This is just a sampling of what's available. Narrow down your options using the following tips.

  • Note specifically what the product is intended for: walls, floors or both. Also, some wall sealers will specify poured concrete walls only, not concrete block.
  • Factor in the number of coats required when looking at coverage figures.
  • Many sealers cannot be applied over any previous sealer, so if this is a recoat situation, select a product that can do that. Remember, even coatings that can be applied over prior coatings require that underlayer to be in good shape.
  • Some products dry clear, some pigmented; some are matte and others glossy. If there’s a decorative look you want to end up with, make sure what you buy is tintable or paintable.
  • Manufacturers specify how long they expect their products to last and often pair that expectation with a warranty — from a couple of years to a lifetime. Pay close attention to the surface preparation and application requirements for your product and pick one with directions you will abide by. Otherwise, the product will prematurely fail and even the best warranty is meaningless.

DIY or Pro?

Homeowners can DIY foundation coatings. Even planning a drainage system and installing a sump pump will be in some homeowners’ skill sets. The problem is knowing which solution is appropriate for your home. If you get a foundation inspection from a structural engineer, that person isn’t invested in the scale of the job. You can then decide if the problems identified are projects you want to tackle yourself or outsource to a pro.


Sealing products start at $150 for 5 gallons, with coverage ranging from 25 to 1,000 square feet per gallon. A foundation inspection from a structural engineer averages $550 nationally, according to HomeGuide data.

How to Repair Foundation Cracks

Your foundation might be doing a fine job of keeping ground moisture out generally speaking, but any crack — even the tiniest — can allow water and water vapor in. It’s your club bouncer checking his socials instead of minding the door.

Identifying the Problem

Many homes will have small cracks somewhere:

  • Wall cracks can run horizontally, vertically and diagonally. Stair-step cracks can happen in the joints of block foundations. Small hairline and shrinkage cracks are common in poured foundations — particularly in newish homes — and often happen during the concrete drying process.
  • Slab cracks can manifest as hairline nothings or those you peer into and wonder whether something may be peering back!

According to Renco, foundation experts in Ottawa, Canada, the following cracks could indicate a bigger foundation problem:

  • Wall cracks running in any direction that you can slide a quarter into.
  • Wall cracks running horizontally of any size.
  • Stair-step cracks in block walls that you can slide a quarter into.
  • Foundation slab cracks larger than a hairline.

Solutions: DIY or Pro?

The cracks listed above should be referred to a foundation professional to determine the underlying cause. Non-worrisome cracks can be DIYed using concrete patch, sealant or low-pressure crack injection with a caulk gun.

Buying Tips

  • Again, ensure you marry your foundation surface and crack size with an appropriate product.
  • As far as injection goes: Epoxy-injection products are the best choice for structural cracks. Polyurethane is what you want for those shrinkage cracks or actively leaking cracks, according to the Concrete Network.


Cement and sealant products are inexpensive, starting at as little as $10. Crack injection kits start at $150 and are sold by footage of coverage (10 feet, 20 feet, etc.). If you get professional help, repairing small foundation cracks will run $250 or more. Larger foundation issues can cost as much as $15,000 to remedy.

What Causes Air Leaks and How to Find Them

Water vapor is the other big issue in basement moisture. Hitching a ride on an air current is a massively efficient way for water to enter a space — more so than seeping through a foundation. It's very common for humid exterior air to sneak into your home through air gaps.

Identifying the Problem

Air leaks require an opening in the building envelope, so they are easy to locate. Check where utility lines, pipes and ductwork pass through a wall or a floor — headed outside and going upstairs. Look at every seam where the floor or ceiling meets the walls.

Tip: has a useful air leak detection method. Turn off your appliances, shut all the doors and windows to the basement then turn on something that exhausts to the outside (a bathroom fan, a portable window fan, the clothes dryer). If you light a stick of incense and bring it close to the locations mentioned, the movement of the smoke will indicate you have air passing there.

Solution: DIY or Pro?

You can caulk those cracks and seal those sill plates. Choose products based on the gap size, the material the product needs to adhere to and whether the gap is stationary.

Caulk: For small gaps (1/4-inch or less) between two immovable materials, caulk is an appropriate choice.

  • Silicone caulk can bond different materials together, is very flexible and can be used on pretty wide gaps but cannot be painted.
  • Latex caulk can be painted but it isn’t as flexible and won’t bond to metal.
  • Only high-temperature caulk should be used for furnace flues.

Polyurethane spray foam: Use this for larger gaps (1/4-inch to 3 inches) between two immovable materials.

  • Spray foam is somewhat flexible, but that flexibility is reduced over time.
  • It is paintable and stainable after it dries.

Weatherstripping: This is a good choice for doors and windows because it maintains flexibility so you can open and close them.

  • Products are made of foam, rubber, plastics and other polymers.
  • Foam tape and wrap expand and contract for uneven gaps around pipes. has a useful table that breaks down the various sealing products.


Starting at a mere $100 in product cost for the entire project, air sealing can be a very inexpensive way to save money and prevent water damage.

How to Fix Moisture Leaks

Basements frequently contain the service lines for the home. And because it is an unfinished space, we aren’t likely hanging out there regularly, so it might take us some time to notice a leak or overflow from a clog. Compounding the difficulty, many leaks aren’t dramatic or they happen only when an appliance or faucet is running.

Identifying the Problem

Follow the service lines and ducts from your appliances to the wall and look for compromised areas, particularly while they're running. Check for these common sources of moisture due to leaks and clogs:

  • Water service line leaks or water heater problems
    When someone is showering, run downstairs and look for pipe leaks. Water heaters can leak at connections and valves, as well as at joints and seams so check all around it. That said, a little condensation could be normal in some environments so don’t bemoan every drop of moisture.
  • AC drain (condensate) line clogs or heating appliances condensating inside
    When the air conditioner or furnace kicks on, go to the HVAC closet and look for unexpected moisture, sounds of dripping or standing water.
  • Basement floor drain clogs
    Look for water collecting at the drain or moist concrete around it. Pour water into the drain and see if it’s draining properly.
  • Dryer ducts that are compromised or detached
    Clean a smooth surface, then run a dryer load and see if you end up with lint where you cleaned. When dryer ducts are disconnected or have a compromised area, they blow lint into the space along with humid air.
Detroit, Michigan -USA- January 12, 2023: home has been updated with a new furnace, hot water tank and electrical panel installed in the basement


Basements usually contain the service lines and major appliances for the home. In an unfinished basement, it can take time to notice a leak or clog. Put regular inspections on your calendar to avoid these unwelcome causes of basement moisture.

Photo by: J.A. Dunbar

J.A. Dunbar

Basements usually contain the service lines and major appliances for the home. In an unfinished basement, it can take time to notice a leak or clog. Put regular inspections on your calendar to avoid these unwelcome causes of basement moisture.

Solution: DIY or Pro?

A little of both.

Plumbing leaks often require a professional touch, but many homeowners can tighten leaking water heater connections. Leaks at valves usually require a professional for assessment. Leaks at seams often mean the water heater is failing, according to Energy Star.

Clogged AC drain lines are one of the most common causes of HVAC repair calls. The pros must be tired of the work because many freely offer the same easy DIY solution on their websites. They maintain that a monthly or bimonthly flush with 1/4-cup of distilled vinegar, followed by water after a 30-minute soak will keep clogs from forming and can even break down existing clogs.

Basement floor drain clogs can sometimes be as easy as removing the cover and dislodging the clog with a gloved hand or drain snake. Floor drains usually have a trap and are routed to a sump pit, or septic or sewer outside. If that doesn’t work and you don’t know where your floor drain goes, you should call a plumber.

Duct leaks can be easily DIYed, either by repair or replacing the piece of compromised duct. In both cases, duct mastic (a paste-style sealant) can be used for bridging gaps and seams 1/4-inch or less. For larger gaps, it’s applied over fiberglass mesh tape. Heat-approved tape is another choice for sealing air and dryer ducts. Effective versions are UL-listed and include mastic, butyl and foil tapes. Find out more at


Plumber and HVAC calls on these issues usually start at $150.

Can Appliances Cause a Wet Basement?

It’s easy to end up with basement moisture just by living our lives. Some condensation will occur in an unconditioned basement because of the temperature difference between inside and outside, the basement and upstairs, the basement air and the service lines and appliances within it. Add to this the humidity generated by showering, cooking and washing clothes. In some home layouts, this moisture gets trapped in the basement.

Identifying the Problem

We mentioned the foil test earlier as one way to tell; another is to purchase a humidity sensor.


All the '-ations': ventilation, circulation and dehumidification!

  • The air circulation provided by the regular use of fans can reduce condensation.
  • Wall vents and windows can allow moist air out of the space and dry air back in, but only if exterior air is dryer than inside. Use a humidity sensor if you're not sure.
  • Dehumidifiers are excellent at managing basement moisture when exterior ventilation isn’t an option. It’s important to note that a dehumidifier is actually the opposite of what you want if your basement water problems are foundation-related. They will accelerate the problem by drawing more moisture inside.

Safety Tip: It may seem strange to say seal everything up, and then tell you to ventilate. But basement waterproofing is about controlling air movement — removing unwanted air sources and keeping, or even adding, the desirable kind. One of the desirables is for your HVAC system. You don’t want your successful air-sealing to have interrupted fresh air access that combustion appliances relied upon for safe operation. So, recommends getting your HVAC contractor out to ensure you got the equation right.


Full-on smart weather stations start at $100, but a humidity detector can be as little as $15. A good shop fan that blows air around your space will run $150 and up. A wall-mounted venting fan with humidity control and two-way operation will draw fresh air in and push basement air out for $230. Dehumidifiers are $180 and up.

Person Removing Air Duct Cover from Ceiling

Controlling, but not eliminating, air movement is part of a basement waterproofing strategy. We do this by sealing air leaks, then adding in our own recipe of ventilation, circulation and dehumidification as needed.

Photo by: Shutterstock/Luluart


Controlling, but not eliminating, air movement is part of a basement waterproofing strategy. We do this by sealing air leaks, then adding in our own recipe of ventilation, circulation and dehumidification as needed.

Final Thoughts

Waterproofing the basement interior and ignoring exterior issues is a recipe for frustration. Check out our article that covers the exterior sources of basement water and how to fix problems. You’ll want to do those first and a few are easy to remedy.

We mentioned at the beginning of this article that basement waterproofing is about both prevention and management. If you want the balance to be in your favor — more prevention than management — then you need to monitor your home regularly. Homes aren’t static: They respond to changes in the environments around and within them. Throw it on the calendar to do a regular walkaround oustide and inside to search for unexpected sources of moisture. Do intermittent checks after major weather events and at season changes. In between inspections, a well-placed leak detector alarm can prevent a burst pipe or appliance failure from having too much fun behind your back.

Don’t forget to check out Energy Star’s explainer for how to benefit from those tax credits we mentioned for your waterproofing endeavors. Insulation products you use in your air-sealing efforts are included.

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