Basement waterproofing: what to know

What the job involves, what changes the price, and what to ask a pro.

What basement waterproofing is

Basement waterproofing stops water from entering a basement through methods such as exterior sealing, interior drain systems, sump pumps, crack repair and improved grading. The right method depends on where the water enters, so the contractor first finds the path the water takes.

Signs you need it

  • Water pools on the basement floor after rain, or a wet line runs along the bottom of the walls
  • Efflorescence, a white powder, or a damp smell shows on the basement walls or floor
  • Cracks in the basement walls are leaking, or the mortar joints in a block wall are wet
  • The sump pit fills quickly or the pump runs constantly, which can mean water is entering faster than the drainage can move it
  • The soil against the foundation slopes toward the house, and the gutters or downspouts dump water near the walls

What the pro does

  • The contractor walks the exterior and interior, checking the grading, the gutters, the downspouts and the wall cracks
  • They locate the water entry points by watching the walls during rain, using moisture meters and the drainage pattern
  • They dig outside the foundation where exterior sealing or drainage is needed, and apply a membrane or coating to the walls
  • They install an interior drain system along the footing that carries water to a sump pit, where a pump moves it away
  • They install or replace the sump pump, the check valve and the discharge line, and test the pump's operation
  • They correct the grading and the downspout discharge so water moves away from the foundation after the work

What changes the price

Every job is different, so we do not publish prices. These are the things that move the quote up or down.

  • Number and length of wall sections affected and whether water enters at one place or several
  • Exterior work needed, such as digging, membrane application and drain tile installation
  • Interior drain system length and whether the floor must be cut and replaced
  • Sump pump type, the pit size and whether a battery backup system is included
  • Crack repair and wall stabilization if the walls are bowing or cracked
  • Grading, landscaping and hardscape that must be removed and restored
  • Access around the house, including fences, decks, driveways and utility lines

What a written quote should spell out

  • Water entry points found, with the method chosen and the reason for it
  • Exterior work listed by wall, with the membrane or coating and the drain tile
  • Interior drain system length, the floor cut and the restoration of the floor
  • Sump pump make, horsepower or capacity, the discharge line and the check valve
  • Grading and downspout correction included, with the discharge location
  • Warranty on the drain system, the pump and the waterproofing, with the length and what is excluded

Questions to ask before you hire

  • Where is the water entering, and how did you confirm the path before recommending the method?
  • Will you dig the exterior, or is an interior system enough for this home?
  • Where does the sump discharge go, and will it drain away from the house?
  • What pump do you install, and does it have a battery backup?
  • Who restores the landscaping, the concrete and the finishes you disturb?
  • Is the warranty transferable if I sell the home, and what does it exclude?
  • Do your own crew do the digging and the pump electrical work, or do you subcontract either one?

Red flags

  • They recommend a sealant or a paint on the walls without finding where the water enters
  • They quote a complete system without going into the basement or checking the grading
  • They discharge the sump water into the yard so it runs back toward the foundation
  • They promise lifetime waterproofing without a written warranty that explains what it covers

What you can do yourself

You can clear the basement of stored items, check that the gutters and downspouts discharge away from the walls, and extend the downspouts. You can also check that the sump discharge line is clear and that it carries the water away from the foundation. Do not dig against the foundation, cut the floor, or install a drain system yourself, and do not work on the sump pump's electrical connection. Call a licensed waterproofing contractor for the wall and drainage work.

Licenses and permits

Basement waterproofing is commonly done by licensed contractors, and digging, drain installation and the pump's electrical connection often need permits or licensed trades. Check with your state or local licensing agency and your local building department for the rules that apply to excavation and drainage work near your home.

Basement waterproofing questions

Do I need to dig outside to waterproof a basement?

Not always. An interior drain system and a sump pump can work well when the water enters along the footing. Exterior work is more complete but more disruptive. Ask the contractor which method fits where the water is entering.

Why does the sump pump run so often?

A pump that runs often can mean water enters quickly, the discharge is too short, or the pump is undersized or failing. Ask the contractor to test the pump and measure the inflow before any replacement.

Will a waterproofing system cause mold?

A system that moves water away from the walls lowers the risk. Moisture can still build up if the basement has poor ventilation or a dehumidifier is needed, so ask the contractor to address the humidity as part of the plan.

About this guide

This national guide is written and checked by infinibell. Rules and conditions differ by place, so local pros are credited on guides for the cities they serve, not on national ones.

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