Checklist: Moisture Problems in the Basement

A damp or wet basement, especially if heated, may generate much more moisture than all other sources combined.

Wall with water damage

Typical Signs

  • Wet or damp floors or walls.
  • White powdery stains on exposed concrete walls or floor.
  • Stains on carpet.
  • Condensation on windows.
  • Rotting windowsills.
  • A stuffy, damp smell.
  • Mould on overhead joists behind insulation.
  • Mould on stored items (that is, cardboard, clothing, etc.).
  • Mould in cold cellar.
  • Mould in corners of outside walls or ceiling.
  • Condensation dripping from cold water pipes.
Leaky faucet

Possible Causes

  • Earth floor in crawl space or basement.
  • Water leaks through cracks in walls or floors.
  • Leaky appliance or plumbing.
  • High RH during the summer.
  • Uninsulated walls.
  • Flooding.
  • High water table.
  • Exterior grading of grass, walks, paved surfaces, gardens near basement walls slopes toward house.
  • Sump pump not operating properly.
  • Open, water-filled sump pump pit.
  • Uncontrolled or improperly set humidifier.
  • Carpet on concrete floor.
  • Hot tub or pool inside home.
  • Firewood stored in basement.
  • Unvented dryer (or dryer duct leaky or disconnected).
  • Wet clothes hung inside.
  • No exhaust fan in bathroom.
  • Items stored against wall or on floor reducing air circulation over cold surfaces.
  • Unheated basement or crawl space.
  • Blocked footing drains.
  • Flue gas condensation leaking from chimney.
  • Spillage of combustion gases from furnace or water heater.
Clothes hanging outside on a line

Practical Solutions

  • Cover earth floor in crawl space or basement with polyethylene with sealed joints or install a concrete floor with polyethylene sheet underneath.
  • Fix cracks and leaks in basement.
  • Excavate and repair/replace exterior moisture barrier system.
  • Fix leaky plumbing and appliances.
  • If the water and/or mould damage was caused by sewage or other contaminated water, call in a professional who has experience cleaning and fixing buildings damaged by contaminated water.
  • Fix landscape grading around the house — ensure all surfaces slope away from the building.
  • Repair sump pump.
  • Install a tight-fitting cover on the sump pump.
  • Do not humidify the home unless absolutely necessary. Ensure controls are operating and properly set if humidifier used.
  • Remove carpets.
  • Cover or empty hot tub when not in use to prevent evaporation.
  • Store firewood outside the house.
  • Vent clothes dryer to outside — ensure joints are sealed with foil tape.
  • Do not hang clothes to dry in the basement.
  • Install bathroom fan ducted to the outside.
  • Minimize stored materials in the basement.
  • Provide sufficient heat to the basement.
  • Have footing drains inspected and improved, if necessary.
  • Dehumidify basement during the warm months (with windows closed).
  • Remove ceiling tiles if they have mould.
  • Insulate cold water pipes with closed-cell foam pipe insulator.
  • Insulate walls (but only if moisture problem solved).



Print(opens in a new window)