Mold can occur naturally on lumber under certain conditions, normally due to the presence of moisture in or on the wood, and warm temperatures. Molds are fungi: ubiquitous organisms that (under proper conditions) can grow on organic matter. Surface molds, which can come from a variety of sources including airborne spores, feed off the sugars and starches readily available in wood.

wood mold and moisture
The intrusion of moisture within the building envelope is the purpose of ongoing studies at this unique research demonstration home built on the grounds of the USDA Forest Products Laboratory in Madison, Wisconsin.

Moisture and Conditions for Wood Decay

When unprotected wood is exposed to the elements, excessive moisture, or contact with the ground, it is susceptible to decay. Four conditions are required for decay to occur: moisture, favorable temperature (approx. 50 to 90 degrees Fahrenheit), oxygen, and a source of food (wood fiber). If any of these four conditions is removed, decay or infestation will not occur. Mold requires moisture to survive, so protecting lumber and wood structures from moisture will prevent mold growth and decay.

Refer to SFPA’s handy tip sheet, Managing Mold & Moisture (download in Publications).

Additional research findings on moisture management are in this report: Insulating Raised Floors in Hot, Humid Climates