In
some cases, indoor mold growth may not be obvious. It is possible that
mold may be growing on hidden surfaces, such as the back side of dry
wall, wallpaper, or paneling, the top of ceiling tiles, the underside of
carpets and pads, etc. Possible locations of hidden mold can include pipe
chases and utility tunnels (with leaking or condensing pipes), walls
behind furniture (where condensation forms), condensate drain pans inside
air handling units, porous thermal or acoustic liners inside ductwork, or
roof materials above ceiling tiles (due to roof leaks or insufficient
insulation).
Some
building materials, such as dry wall with vinyl wallpaper over it or wood
paneling, may act as vapor barriers, trapping moisture underneath their
surfaces and thereby providing a moist environment where mold can grow.
You may suspect hidden mold if a building smells moldy, but you cannot see
the source, or if you know there has been water damage and building
occupants are reporting health problems. Investigating hidden mold
problems may be difficult and will require 
caution
when the investigation involves disturbing potential sites of mold growth—make
sure to use personal protective equipment. For example, removal of
wallpaper can lead to a massive release of spores from mold growing on the
underside of the paper.
Mold Prevention Tips
- Fix leaky plumbing and leaks in the building envelope as soon as possible.
-
Watch for condensation and wet spots. Fix source(s) of moisture problem(s) as soon as possible.
-
Prevent moisture due to condensation by increasing surface temperature or reducing the moisture level in air (humidity). To increase surface temperature, insulate or increase air circulation. To reduce the moisture level in air, repair leaks, increase ventilation (if outside air is cold and dry), or dehumidify (if outdoor air is warm and humid).
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Keep heating, ventilation, and air conditioning (HVAC) drip pans clean, flowing
properly, and unobstructed. - Vent moisture-generating appliances, such as dryers, to the outside where possible.
- Maintain low indoor humidity, below 60% relative humidity (RH), ideally 30-50%.
- Perform regular building/HVAC inspections and maintenance as scheduled.
- Clean and dry wet or damp spots within 48 hours.
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Don't let foundations stay wet. Provide drainage and slope the ground away from the foundation.
Safety
Tips While Investigating and Evaluating
Mold and Moisture Problems
- Do not touch mold or moldy items with bare hands.
- Do not get mold or mold spores in your eyes.
- Do not breathe in mold or mold spores.