The 2021 S500 (5th edition) sets the class by how much of the room’s total surface area (floor + walls + ceiling) is wet, not by how high water wicked. Enter the room and what you measured wet.
How the 2021 S500 sets the class
The 5th edition classifies a water loss by the share of the space’s combined floor, wall and ceiling surface area that is wet: under 5% is Class 1, 5% to 40% is Class 2, over 40% is Class 3. Class 4 is deeply held water in low-evaporation materials such as hardwood, plaster and concrete. Older editions used how far water had wicked up the walls, so many references online still describe it that way.
Worked example: a Class 2 water loss
A 20 × 15 ft room with 8 ft ceilings has 1,160 ft² of floor, wall and ceiling surface. With the whole 300 ft² floor wet and 35 ft of wall wet to 1.5 ft, about 353 ft² is wet: 30%, a Class 2 water loss.
Why the class matters
Class sets the evaporation load, which drives how many dehumidifiers and air movers the job needs and how long drying should take. Get it right at inspection and re-assess as the job changes.
Frequently asked
What is a Class 2 water loss?
Under the 2021 S500, a Class 2 water loss is one where 5% to 40% of the combined floor, wall and ceiling surface area in the space is wet. Under older editions it meant a whole room with water wicked up the walls less than 24 inches.
What is the difference between water category and class?
Category is about contamination (clean, gray or black water). Class is about how much is wet and how hard it is to dry. Every water loss has one of each.
Do I count the ceiling if it is dry?
Yes. The total includes the floor, walls and ceiling of the space whether or not they are wet; only the wet portion counts toward the percentage.
More free tools
This knowledge, built into the software
RestoredOS runs the whole job on the same field knowledge behind these tools — drying logs, moisture mapping, scope, and billing.