Classes of Water Loss
Class 1: Slow Rate of EvaporationWater losses that affect only part of a room with low-permeance/porosity materials (e.g. plywood, particle board, structural wood, VCT, concrete). Little or no wet carpet and/or cushion is present (or damage confined to a small area, or wet for a short period). Minimum moisture is absorbed by materials, which release that moisture slowly.
Class 2: Fast Rate of EvaporationWater losses that affect the entire room of carpet and cushion. Water has wicked up walls less than 24 inches. There is moisture remaining in structural materials (e.g. plywood, particle board, structural wood, VCT, concrete).
Class 3: Fastest Rate of EvaporationWater may have come from overhead. Ceilings, walls, insulation, carpet, cushion, and subfloor in virtually the entire area are saturated.
Class 4: Specialty Drying Situations
These losses involve wet materials with very low permeance/porosity (e.g. hardwoods, subfloors, plaster, brick, concrete, stone, crawlspaces). Typically, these are deep pockets of saturation, which normally require very low specific humidity.