Class 1 to 4 water intrusion: how much has to be dried?

In plain English

Where the category describes how dirty the water is, the class describes how big the drying job is: an estimate of how much water has to be evaporated, made at the start of drying. It depends on how much wet surface there is and how readily the wet materials give up their water.

Class 1 is the smallest job: wet porous materials like carpet, drywall and insulation make up less than about 5% of the room's combined floor, wall and ceiling area. Class 2 runs from about 5% to 40%. Class 3, the largest evaporation load, is more than about 40%. Classes 1–3 also assume that slow-drying materials have taken on very little water. Class 4 covers jobs where a lot of water has soaked into those slow-drying materials (plaster, wood, concrete, masonry) or into layered assemblies like multilayer drywall, multilayer subfloors and gym floors; they can need special methods, longer drying, or a large vapor pressure difference.

The class is worked out from what the inspection finds, and it can depend on which wet materials are being kept and whether the restorer can get at them — so on some jobs it is settled later in the first response rather than on arrival. Other factors, from weather to available power, also shape how much humidity control a job needs.

The class drives how many dehumidifiers and air movers a restorer brings and how long drying should take, so it is worth understanding when you read a water-damage estimate.

Key points

• Class 1: under ~5% of surfaces wet.
• Class 2: ~5% to ~40%.
• Class 3: over ~40%.
• Class 4: slow-drying, low-evaporation materials.

Official text

This topic is covered in our own words because the standard behind it is copyrighted; we cite it below rather than reproduce it.

Citations

• IICRC S500, ANSI/IICRC S500 Standard for Professional Water Damage Restoration — Definitions, “Class of water intrusion,” p. 16. Best practice
• IICRC S500, ANSI/IICRC S500 Standard for Professional Water Damage Restoration — Secs. 10.4.3–10.4.4, Class of Water Intrusion; other factors in estimating humidity control, pp. 45–46. Best practice

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