Checklist: Moisture Problems in Exterior Walls

Moisture in exterior walls can come from exterior and interior sources.

Wall with paint flaking off

Typical Signs

  • Condensation on walls.
  • Bulging, buckled or rotting siding.
  • Blistering or flaking paint.
  • Appearance of frost condensation.
  • Wet stains or chalky deposits on brick or stucco.
  • Moisture-damaged window and door frames.
  • Moisture damaged drywall and flooring inside house next to exterior walls.
  • Damp or wet flooring at base of walls.
Downspout with the end missing

Possible Causes

  • Warm, moist, inside air leaking into exterior walls where the moisture can condense and wet surrounding materials.
  • Wind-driven rain causing water to penetrate the wall cladding from outside.
  • Inadequate or missing flashings around windows, doors, joints, etc.
  • Overflow of rain barrel not properly drained.
  • Broken downspout or downspout termination on foundation.
  • No eavestroughs or gutters.
  • Broken, clogged or poorly sloped eavestrough/gutter.
  • Backsplash of rain from hard ground surfaces back onto walls.
  • Siding installed too close to ground with less than 200 mm (8in.) of clearance.
  • Poor drainage from porches and decks.
  • Outdoor tap/garden hose leaking against wall.
  • Little or no wall insulation causing condensation to occur.
Person cleaning out an eaves trough

Practical Solutions

  • Inside the home, seal all openings into outer walls that would allow air leakage.
  • Reduce excess moisture in the house.
  • Improve house ventilation.
  • Install or repair flashing to lead rain away from wall.
  • Direct overflow spout of rain barrel away from walls and foundation.
  • Repair broken downspouts.
  • Install and properly slope eavestroughs/ gutters and extend away from the house.
  • Repair or clean out eavestroughs/ gutters to prevent overflows.
  • Re-grade ground to drain surface water away from building.
  • Fix leaky tap. Add hose extension to minimize water pooling under foundation.
  • Provide adequate clearance between siding and ground and decks, patios.
  • Caulk and seal exterior joints around windows, doors, joints in siding, flashing, balcony framing.
  • Ensure walls are well insulated and air sealed.



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