Slow Rate of Evaporation: The Least amount of Water - Air Movers placed 16LF Apart

Water losses that could affect only part of a room or area: or even large losses containing low permeance/ porosity materials (e.g., plywood, particle board, structural wood, VCT, concrete.) Little or no wet carpet and / or cushion is present. Minimum amount of moisture can be held in the remaining structural materials.

Class 2:

Fast Rate of Evaporation - More water than Class 1 - Air Movers placed 14LF Apart

Water losses that affect the entire room of "Carpet and Cushion" or several rooms of a large structure with "Carpet and Pad". Water has wicked up the walls as much as 24 inches. There is moisture remaining in structural materials (E.G., plywood, particle board, structural wood, VCT, concrete.) Due to the amount of water held in dirt or mud, crawlspaces, in most circumstances, will also fit under a class 2.

Class 3:

Fastest Rate of Evaporation - Most Amount of Water - Air Movers placed 12LF Apart

Water may have come from overhead. Everything is wet. Must have carpet and pad. Ceilings, walls, insulation, carpet, cushion, and sub floor in virtually the entire area are saturated.

Class 4:

Specialty Drying Situations - Specialty Drying Situations - Air Movers placed 16LF apart

These losses involve wet materials with very low permeance/porosity (E.G., hardwoods, sub floor, plaster, brick, concrete, stone). Class 4 differs from a Class 1 due to the deep pockets of saturation that require the use of a desiccant or low grain dehumidifier to achieve very low specific humidity and time. Even then, the Class 4 drying job will take more time - longer to dry - than a typical Class1

* Except from the IICRC Standard S500: Standard and Reference Guide for Professional Water Damage Restoration.  3rd Edition.