Where the water comes in
Some Triangle houses have basements, including walkouts built into sloped lots, and basements leak in a handful of predictable places:
- The joint where the wall meets the floor. The floor slab is poured separately from the walls, and water under pressure in the soil outside finds that seam first.
- Cracks in the wall, especially ones that let water through after every heavy rain.
- Window wells that fill with water and leaves and let it in around the window.
- Through the wall itself, where a concrete block wall shows a damp band or white mineral deposits.
- The uphill wall of a walkout, where water moving downslope through the soil meets the foundation.
The first question is whether the water tracks the weather. Water that arrives with heavy rain is coming from outside. Water in a dry spell, or water rising from a floor drain, is more likely a supply leak or a sewer backup, and repairing plumbing for pay in North Carolina requires a licensed plumbing contractor under G.S. 87-21. That is a different first call.
Fix the outside first
None of these is basement waterproofing, and all of them are cheaper than any of it:
- Extend the downspouts so roof water lands well away from the foundation.
- Correct the grade so the soil falls away from the house on every side. Backfill along a foundation settles and often ends up sloping toward the wall.
- Clear and cover the window wells.
- Check the irrigation. A sprinkler soaking a foundation wall every morning is a water source that has nothing to do with the weather.
Before anyone digs - to bury a downspout line or excavate a wall - NC 811 is the free service that locates buried utility lines.
Interior drain and sump, or exterior waterproofing
These are the two main approaches, and they solve different problems.
| Interior drain and sump pump | Exterior waterproofing | |
|---|---|---|
| What it is | A drain at the base of the wall inside the basement, under or beside the floor slab, carrying water to a sump basin and pump | Excavating the soil from outside the wall, coating or wrapping the wall in a waterproof membrane, and laying a drain at the footing before backfilling |
| What it does | Collects the water that reaches the wall and pumps it out before it spreads across the floor | Keeps water off the outside of the wall in the first place |
| Disruption | Inside the basement: the floor along the wall is cut and repoured | Outside: the yard, plantings and anything against the wall are dug up |
| Best suited to | Finished basements, walls that are sound, and houses where digging outside is impractical | New construction, additions, walls that need protecting, and walkouts where the wall is reachable |
| Ongoing care | Test the pump before storm season; consider a battery backup and a high-water alarm | Keep the footing drain outlet clear |
North Carolina’s residential code treats these as separate subjects: foundation drainage has its own section (R405), and waterproofing a concrete or masonry foundation wall has another (R406.2), which lists the membrane materials it accepts, from 40-mil polymer-modified asphalt to 6-mil polyethylene (NC Residential Code, chapter 4). A quote for exterior work should name the membrane it uses.
Coatings painted on the inside of a basement wall are also sold as waterproofing. If one is proposed for a wall that leaks every storm, ask what it is rated to resist and why it will hold where the water is arriving.
Cracks and the wall itself
Sealing a crack - usually by injecting it from inside - stops water coming through that crack. It does nothing about water at the wall-floor joint or through the rest of the wall, and it is not a structural repair. A crack that is widening, a wall that is bowing inward, or a floor that is settling is a question for a foundation specialist or a structural engineer, not a waterproofing crew, and this site does not route foundation repair.
Basement or crawl space?
If the space under your house is a crawl space rather than a basement, the same trade applies with different details: an interior drain in the dirt floor, a sump basin dug rather than cut, and a vapor barrier once the floor stays dry. Crawl space waterproofing and drainage covers that version.
What it costs
Published national figures disagree more for basement waterproofing than for almost anything else on this site. Angi’s basement waterproofing cost guide (updated July 2026) says most homeowners pay $2,461 to $8,202, with an average of $5,241, and that minor interior fixes such as sealing foundation cracks can cost as little as $600. HomeGuide’s guide puts interior systems at $6,000 to $12,000 and exterior waterproofing at $10,000 to $18,000. Neither publishes a Triangle rate.
The gap is mostly scope. A crack injection, an interior drain along one wall, and a full exterior membrane are all called basement waterproofing. What moves the number:
- Interior or exterior, and how many walls.
- Linear feet of drain, and whether a sump and discharge line are included.
- Access and finishes. A finished basement or a wall under a patio costs more to reach.
- The pump. A battery backup and a high-water alarm are worth pricing in at the start.
The bid checker lists what a written quote should specify, and every published range on the site is on the cost hub.
Questions to ask before you hire
- Where exactly is the water getting in, and what did you see that tells you so?
- Have the downspouts and grading been checked, and would fixing them change what you are proposing?
- Is this an interior or exterior system, how many feet of drain, and where does the discharge end?
- For exterior work, which membrane are you using, and how is the drain at the footing connected?
- Does the price include a battery backup and an alarm for the pump?
- What does the warranty cover, in writing?
- Will this need a permit?
The next step
A short description of when the water appears and where it comes in is enough to start with. Describe what you are seeing and we will follow up to schedule a free inspection. There is no obligation to hire anyone.
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