Investigating moisture problems is more direct than for most air pollutants, because we can see and smell and feel the evidence of water (H2O) as liquid/vapor/moisture/humidity.

Testing for moisture

  • Notice upon entering if you feel high humidity; test using a relative humidity (%RH) meter.
  • Use your eyes to find dampness, stains, damage, efflorescence.
  • Use your nose to find hidden moisture (damp earth or walls, and possibly mold, sewer gas).
  • Test for damp materials using portable continuous direct-reading survey meters (see separate how-to page), either
    • a pad-type (pinless) meter that sends radio waves through the material:
      • regular shallow (an inch) meter to check just under the surface, or
      • deep (several inches) “wet-wall” meter to check across insulation or a wall cavity, and/or
    • a pin-type meter that pokes needles into the material either
      • for surfaces (millimeters), or
      • for deep underlayers (several inches) using a slide hammer.
    • (Deep testing is used for EIFS siding.)
    • (Both types are “penetrating”, with either radiation or pins.)

Sources of moisture

  • Breathing is usually the main moisture source.
  • Water intrusion more locally, from indoors and outdoors, such as:
  • Plumbing leaks from connections, appliances, or clogged drains, from a source usually hidden (wall cavities, under sinks).
  • Rainwater leaks in the building envelope (roof, windows, sliding doors, walls, basement).
  • Damp areas (basement walls, crawl space, surrounding earth).
  • Local dampness indoors (plants, aquarium).
  • New building materials (concrete, lumber, paint).
  • Cooking, especially with gas (unless using an exhaust fan).
  • Bathroom exhaust fan vented into the attic or crawl space.
  • Activities (bathing, clothes dryer).

Excessive moisture

  • Damp or wet materials.
  • Moisture condensation on cold surfaces from contact with warm, moist air.
  • Certain conducive conditions foster moisture problems, such as:
  • Furniture that blocks airflow and make an exterior wall colder.
  • Window coverings that block airflow and make the window colder.
  • High humidity indoors that increases condensation and slows evaporation.
  • Inadequate ventilation to dump excessive moisture.
  • Exterior siding that traps moisture between wood and impermeable foam insulation (like EIFS, exterior insulated finishing system).
  • Earth (soil, bushes, moss, landscape materials) in contact with wood structure.
  • Debris (especially cellulose) that holds moisture.
  • Water splashing or pooling near the exterior

Effects of moisture

  • Moisture stains and damages materials.
  • Excess moisture allows the growth of molds, rot, and bacteria.
  • Moisture increases the release of formaldehyde from materials containing urea-formaldehyde resins (particle board).

Controlling moisture

  • Stop leaks.  Dry out materials.  Ventilate more.

Problems in Buildings

The following pages are about “Mold and Moisture Problems in Buildings“: