Where preservative-treated wood is used in enclosed locations where drying in service cannot readily occur, the wood must have a moisture content of _____% or less before being covered with materials.

When using preservative-treated wood in enclosed locations where drying in service is unlikely, it is crucial that the wood has a moisture content of 19% or less before it is covered with other materials. This moisture content threshold is established to prevent issues such as mold growth, wood decay, or deterioration of the preservative treatment itself, which can occur if the wood retains too much moisture.

Having the moisture content at or below 19% ensures that the wood will be sufficiently dry to allow for safe installation and to promote longevity in the building structure. It minimizes the risk of environmental issues and extends the effectiveness of the chemicals used in the wood treatment process. Choosing a higher moisture content could lead to problems, resulting in potential structural failures or health risks due to moisture-related mold or fungus. Therefore, adhering to this 19% moisture content guideline is essential for maintaining the integrity and safety of the construction.