Where below-grade moisture comes from
- Surface water: rain and snowmelt running toward the foundation because of poor grading, clogged gutters or short downspouts. This is the most common cause and often the cheapest to fix.
- Groundwater: water in the soil pushing against walls and floors, especially in wet seasons or areas with high water tables.
- Plumbing leaks from supply lines, drains and water heaters.
- Condensation when warm, humid air meets cool concrete walls and floors.
- Vapor moving through concrete and from exposed soil in crawlspaces.
Identifying the source matters, because the fix is different for each.
Start outside
- Clean gutters and make sure they're sized for the roof.
- Extend downspouts several feet from the foundation or connect them to a drainage system.
- Grade soil so it slopes away from the house.
- Keep window wells clear and covered, or drained.
- Don't let sprinklers spray the foundation.
These steps solve many basement and crawlspace water problems without major work.
Waterproofing options
- Crack injection seals leaking cracks in poured concrete walls.
- Interior drainage systems collect water at the base of the walls, under the floor's edge, and carry it to a sump pump. They manage water rather than stopping it from entering the wall.
- Exterior waterproofing excavates around the foundation, applies a waterproof membrane, and installs drain tile at the footing. It stops water at the outside of the wall but is more disruptive and expensive.
- Wall coatings applied inside can reduce dampness from vapor but don't stop water under pressure.
Crawlspace encapsulation and moisture control
Crawlspaces with exposed soil release a great deal of moisture into the space and the house. Common improvements include:
- A heavy vapor barrier covering the soil and sealed at seams and walls.
- Drainage and a sump pump if water collects.
- Sealing vents and conditioning the space, or keeping it vented and dry, depending on climate and code. Approaches differ, and local code and climate determine what's appropriate.
- A dehumidifier in sealed crawlspaces.
- Insulation on the walls or under the floor, depending on the design.
Dehumidifiers
Basements and crawlspaces often need a dehumidifier to keep relative humidity low enough to prevent mold. Many guidelines suggest keeping it below about 50 to 60 percent. Units with a drain line to a sump or floor drain don't need emptying.
Questions to ask
- Where is the water coming from, and how did you determine it?
- Can grading, gutters or downspouts solve it before waterproofing?
- Interior or exterior waterproofing, and why?
- For crawlspaces, will you seal or vent it, and what does local code require?
- What warranty covers the work?
Signs to watch for
- White, chalky deposits on concrete walls, called efflorescence, left behind when water evaporates through the concrete.
- Peeling paint or coatings on basement walls.
- Rust on appliance legs, nails or metal posts.
- A musty smell that's strongest below grade.
- Condensation on cold water pipes and windows.
- Wet or sagging insulation in a crawlspace.
Order of operations
Work from the outside in and from the cheapest fix to the most expensive: gutters, downspouts and grading first; crack repair next; then interior drainage, a sump pump or exterior waterproofing if water still gets in. Add humidity control once water entry is solved. Skipping straight to the most expensive option often leaves the real source untouched.
When moisture affects the rest of the house
Air from basements and crawlspaces moves up into living spaces. A damp crawlspace can make the whole house smell musty and raise indoor humidity. Fixing the below-grade moisture often improves comfort and air quality upstairs as well.