Checklist: Moisture Problems in Bathrooms

Bathrooms generate a good deal of moisture through showers and bathing. Ventilation is important.

Tiles around a bathtub that are mouldy

Typical Signs

  • Condensation on windows.
  • Condensation or staining on walls or ceilings.
  • Water dripping from exhaust fan grille.
  • Mould between ceramic tiles.
  • Rotting windowsills.
  • Damaged gypsum board under windows.
  • Bulging gypsum board.
  • Peeling paint or wallpaper.
  • Musty smells.
  • Visible mould damage, staining or growth on floor or carpet.
  • Curling floor tiles.
  • Loose floor and wall ceramic tiles.
  • Water pooling around toilet, sink or tub.
  • Toilet is unstable — moves easily.
  • Mould on walls or ceiling.
  • Condensation on toilet tank.
  • Mould under toilet tank.
Water sitting on a tile floor

Possible Causes

  • Leakage, spillage from bathtubs and shower stalls during use.
  • Moisture (often referred to as “steam”) from hot baths and showers.
  • No bathroom fan.
  • Bathroom fan not used.
  • Uninsulated exhaust fan duct — condensation forms in cold duct.
  • Backdraft damper on exhaust fan housing inadequate — allows cold air in from outside when fan not operating, which cools surfaces and makes them prone to condensation.
  • Leaky plumbing.
  • Plumbing leaking behind walls.
  • Dampness from wet bath mats, towels and drying clothes.
  • Inadequate air circulation.
  • Temperature kept too low/poor heat distribution to bathroom.
  • Seal lost around shower stall or tub, cracks in tiles.
  • Uninsulated toilet tank resulting in cold tank surface and humid weather condensation problems.
Person cleaning tiles with a Squeegee

Practical Solutions

  • Turn on exhaust fan when showering or taking a bath.
  • Install a bathroom fan exhausted to outside (windows are not a reliable source of ventilation).
  • Allow fan to run for 15 minutes or longer after the shower or bath to remove moisture.
  • Squeegee or towel dry surfaces in the shower stall or bath enclosure after use.
  • Close bathroom door and run bathroom fan when showering.
  • Install a humidistat that turns exhaust fan on and off automatically.
  • Fix leaky plumbing.
  • Supply adequate heat and ventilation to the bathroom.
  • Caulk joints in shower stall, tub and around sink. Repair/replace/seal grout joints in tiled floors and walls.
  • Properly insulate walls and ceilings.
  • Consult a professional contractor for replacement of mouldy walls.
  • Have insulated exhaust fan ducts properly installed.
  • Remove carpet.
  • Install a 4.5-litre (1-gallon) toilet — these do not tend to “sweat” as they hold less cold water.
  • Clean surfaces regularly.



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