Basement Waterproofing

A wet basement is almost always a water-pressure problem. When the soil around your foundation fills with water after rain or snowmelt, that water pushes against the walls and up under the floor (hydrostatic pressure). It finds the weakest spots: the joint where the wall meets the floor, cracks, mortar joints, pipe penetrations and window wells.

The main waterproofing methods

Interior drainage system (drain tile)

The most common and usually most cost-effective permanent fix. A contractor removes a narrow strip of the floor along the walls, installs a perforated drain pipe in gravel and connects it to a sump pump. Water that reaches the wall is captured and pumped out before it can spread across the floor. A dimpled membrane on the walls guides seepage down into the drain.

Exterior waterproofing

The soil around the outside of the foundation is dug out, the wall is cleaned, sealed with a waterproof membrane and a new footing drain is installed. It stops water at the source but is more expensive and disruptive, especially near driveways, porches and landscaping.

Crack injection

Isolated cracks in poured-concrete walls can be sealed from inside with polyurethane or epoxy injection. It is fast and affordable when a single crack is the only problem.

Sump pumps and backups

A good pump in a sealed pit, sized for your water volume, plus a battery or water-powered backup for power outages. More about sump pumps.

Grading, gutters and downspouts

Often part of the solution: soil should slope away from the house and downspouts should discharge several feet from the foundation.

Typical costs

Project	Typical range*
Crack injection (per crack)	$300 – $1,000
Sump pump installation or replacement	$800 – $2,500
Interior drainage system (full perimeter)	$4,000 – $12,000
Exterior excavation & membrane	$10,000 – $25,000+

*General US ranges for orientation only. Your contractor gives you an exact price after looking at your home.

Signs you need basement waterproofing

• Water or damp spots along the floor edge after rain
• White, chalky residue (efflorescence) on walls
• Musty smell, mold or mildew
• Peeling paint, rusting appliance feet, warped trim
• Wall cracks, especially horizontal ones
• A sump pump that runs constantly