• Lowered air conditioner thermostat setting (typically 68-73oF), below the ambient dew point.
• Negative pressures across the envelope from high supply duct leakage (cfm @25Pa > 10 per 100 square feet of conditioned floor area), inadequate return air paths, interior door closures, exhaust fans or a combination thereof.
• Inadequate moisture removal from disconnected return ducts, fans always on (air handler or ventilation), inadequate drainage of condensate, oversized air conditioner or a combination thereof.
• Moisture diffusion from the ground into the house because of poor site drainage, inadequate crawl space ventilation, tears in the belly board, or a combination thereof.
• Vapor retarder in the wrong location i.e. vinyl or other impermeable wall or floor coverings located on the colder surfaces.

Recommended solutions provided to the manufacturers to eliminate moisture problems include:

• Maintain air conditioner thermostat above the ambient dew point (at least 75oF )
• Eliminate long term negative pressures created by air handler fans or ventilation equipment.
• Tightly seal all ductwork and provide adequate return air pathways.
• Enhance moisture removal from the conditioned space by correct sizing and maintainence of equipment
• Eliminate ground source water and provide adequate moisture barrier for the floor assembly
• If possible, remove vapor barriers located on the wrong surfaces.

Work is continuing to determine if these steps will be sufficient to prevent problems even in the presence of vapor barriers in the wrong locations for the hot, humid climates that are preferred by manufacturers and customers.