The Homeowner’s Ultimate Basement Waterproofing Guide

Having a dry basement is important for preserving the integrity of the house’s structure and for keeping items like furniture, appliances and valuables safe.

A dry basement is also important for increasing additional living space. When remodeling the basement for use as a home office, recreation room, guest bedroom or rental apartment, the basement must be dry in order to install walls, flooring, ceilings and electrical and plumbing systems.

Safety Concerns

A dry basement is important for safety and health in three ways:

• Preserving the structure: A wet basement can weaken structural elements, leading to costly repairs or even collapse. A dry basement encourages studs, joists, beams and columns to stay in good shape.
• Preventing mold growth: Moist basement environments can lead to mold growth. Some types of black mold have been linked to respiratory issues and allergies, as well as to more minor conditions like stuffy noses, sore throats and burning eyes.
• Improving indoor air quality: A damp basement is musty and unpleasant. A dry basement eliminates the conditions that lead to poor air quality.

Wet basements can be caused by interior reasons, such as condensation or leaky pipes, or by exterior reasons, like groundwater or poor drainage.

Interior Condensation

When the air in the basement is too humid, water can condense on the walls and floor. Water can also condense on the walls when there is a sharp temperature difference between cold walls and warm air.

Cracked Foundation Walls

When foundation walls are cracked or have holes, water can seep in from groundwater or from on-grade water.

Windows and Doors

Water can migrate into the basement through basement windows and doors. Water can also leak through upper-floor windows and doors, through the walls and down to the basement.

Leaky Pipes

Basements usually contain the majority of a home’s mechanicals: furnaces, AC units, pipes, water heaters and more. Water supply pipes run through the ceilings of basements and can leak.

Groundwater

Groundwater is water that has soaked into porous soil through dirt, sand and rocks. Groundwater may come up through a basement floor or from the side, through foundation walls.

Fill Cracks

Cracks in basement foundation walls can be filled with hydraulic cement. The cement is mixed with water and then forced into the cracks by hand or with a putty knife. It then expands to fill the crack.

Seal Walls

If a moisture tester indicates that water is seeping through the basement walls from the outside, a masonry waterproofing product can be applied to stop the moisture. Two coats of the waterproofer can act as a barrier against trace amounts of external water.

Add Interior French Drain

An interior French drain is a trench in the floor of the basement that provides a channel for water to flow to a sump basin. Filled with perforated pipe and gravel, the French drain diverts water away from other parts of the basement and to the sump pump basin, where the sump pump expels it to the outside.

Grade the Yard

Grading the yard sends exterior water away from the foundation and the basement. A homeowner with a shovel, wheelbarrow and extra fill dirt can grade the soil in a day or two.

Install or Improve Gutters

Gutters capture roof water runoff and direct it away from the foundation and the basement. Most homes need gutters. But homes surrounded by concrete hardscaping or homes that are on downward slopes or with long roof overhangs may not need gutters.

Seal Exterior Foundation Wall

Basement foundation walls can be sealed against water with a liquid synthetic membrane, solid sheets of bentonite or synthetic sheet membrane. A cementitious coating can be applied to the outside of the basement walls for extra moisture protection.

All exterior foundation sealing methods require soil to be dug out from alongside the foundation wall to the bottom. Drain tile may also be added to the bottom of the trench to help with drainage.

Install Exterior French Drain

A French drain is a trench lined with gravel, perforated pipe and weed-block fabric. Water enters the trench and is moved to the end of the pipe, away from the foundation and basement. French drains work well for yards where pooled water seeps toward the basement walls.

The national average cost to waterproof a basement ranges between $2,300 and $6,800. Most homeowners pay an average of $4,500 to $4,600 to waterproof their basements.

Estimating the cost to waterproof a basement on a square foot base, most homeowners pay $3.70 per square foot at the low end and $10.00 per square foot at the high end. On average, most homeowners pay $6.85 per square foot to waterproof their basements.

Basement moisture that comes from the outside usually requires both outside and inside waterproofing methods.

Basement moisture that comes from the inside only—such as condensation and leaky pipes—requires no outside waterproofing methods. The project is less waterproofing than it is moisture maintenance. Equalizing water and air temperature to prevent condensation, running dehumidifiers, fixing leaky pipes and repairing or replacing water-dependent devices (water heater, HVAC system or clothes washer) helps eliminate interior water in the basement.

1. Inspect gutters and downspouts regularly
2. Grade soil away from the home
3. Keep your basement well-ventilated
4. Use dehumidifiers
5. Install a sump pump and regularly inspect it
6. Repair cracks or holes in the foundation
7. Seal cracks and holes in windows and doors
8. Install drain tiles at the base of the exterior foundation
9. Add weatherstripping to windows and doors
10. Add extensions to downspouts

Hiring a basement waterproofing professional is an important first step in protecting your basement from water damage. When hiring a basement waterproofing professional:

• Research well: Consult friends, family members or neighbors for recommendations and check online reviews.
• Check trade organizations: Check professional organizations like the Basement Health Association, which maintains a member database.
• Verify credentials: Verify that the professional is licensed and insured to work in your area.
• Ask for references: Ask the waterproofing professional for references from past customers and follow up with those references by calling or by emailing them.

To arrive at the average costs in this article, one basement waterproofing provider and three cost databases were surveyed on national and local levels. All averaged figures were correct at the time of publication and may be subject to change.