Affected-Material Categorization, Class and Category Logic

Why this matters

The IICRC S500 "Class" and "Category" terms are the two axes that drive the entire restoration scope and price. Misclassifying a Class 4 (deep-pocket-saturation) job as a Class 2 (carpet plus pad) under-bills the equipment, under-times the drying, and leaves wet substrate behind that grows mold in week three. Misclassifying a Cat 2 dishwasher overflow as Cat 1 skips the antimicrobial step and triggers a recall. This guide is the field decision flow for getting the classification right on the first walkthrough.

The two axes

Category answers "how contaminated is the water source." Three values:

• Cat 1: clean water from a sanitary source.
• Cat 2: significantly contaminated, gray water.
• Cat 3: grossly contaminated, black water.

Class answers "how much material is wet, and what kind of materials are involved." Four values:

• Class 1: minimal absorption, hard surfaces only, less than 5 percent of perimeter of the affected area has wet porous materials.
• Class 2: significant absorption, wall wicking under 24 inches, some carpet/pad involvement.
• Class 3: water has saturated overhead (ceiling), entire surfaces of porous materials wet, wall wicking above 24 inches.
• Class 4: water has saturated low-permeance materials (hardwood, plaster, concrete, brick, stone) that require special drying.

Category and Class combine. A Cat 3 Class 2 job (sewage backup contained to a small area) is a very different scope from a Cat 1 Class 4 job (broken supply line that ran for days into hardwood and plaster).

Category determination walkthrough

Start with the source. The plumber's report, the homeowner's narrative, and your own inspection of the source line tell you the starting category.

1. Clean source, less than 48 hours, no contact with contaminated material. Cat 1.
2. Clean source, more than 48 hours OR has contacted contaminated material (soiled carpet, dust on a subfloor, etc.). Cat 2 by promotion. S500 Section 10.5.5 is explicit.
3. Source includes detergents, soaps, food residue, washing-machine discharge. Cat 2 from the start.
4. Source includes sewage, fecal material, raw sewage, river/storm floodwater, toilet overflow past the trap. Cat 3 from the start.
5. Mixed source (broken supply line dripping into a basement that already has rodent contamination). Cat 3 by promotion. The worst contamination on the affected materials sets the category for those materials.

Document the source and the start time as accurately as the available information allows. The 48-hour clock is the most-litigated time stamp in restoration claims.

Class determination walkthrough

After category, walk the affected area with a moisture meter.

Class 1 indicators

• Hard-surface flooring only (tile, sealed concrete, vinyl).
• No carpet or pad in the affected area.
• Wall affecting under 5 percent of room perimeter, and only at the baseboard.
• Drywall moisture at or near unaffected reference.

Example: small ice-maker line leak in a tiled kitchen, water spread 30 square feet across the tile, baseboards on one short wall show 1 to 2 inches of wicking. Class 1 with limited drying.

Class 2 indicators

• Carpet and pad in the affected area, wet.
• Wall wicking up to 24 inches above the floor.
• Affected perimeter 5 to 40 percent of the room.
• Affected substrates are mostly standard absorptive materials (drywall, fiber padding) without dense or low-permeance materials.

Example: water heater failure in a finished basement, 200 square feet of carpet and pad wet, drywall wicked 18 inches up two walls. Class 2.

Class 3 indicators

• Water came from above (ceiling).
• Walls wet above 24 inches.
• Insulation wet (fiberglass, cellulose, mineral wool).
• Multiple porous materials saturated.

Example: second-floor toilet supply-line burst, water flowed through ceiling joist bays to the first-floor ceiling, with drywall ceiling sagging, walls wet to 4 ft up. Class 3.

Class 4 indicators (the upgrade)

Class 4 is a separate determination on top of Class 1, 2, or 3. It applies when low-permeance materials (densely absorptive or very low-vapor-permeability materials) are wet and require special drying:

• Hardwood flooring saturated through to the subfloor.
• Plaster walls (over wood lath or metal lath) wet.
• Concrete or masonry wet, particularly polished, sealed, or coated concrete.
• Dense wood structural members (glulam, LVL) wet.

Class 4 requires either targeted heat, hardwood drying mat systems (Drieaz Rescue Mat, Injectidry), or desiccant equipment, in addition to standard refrigerant dehus and air movers. Time-to-dry is 5 to 10 days minimum, sometimes much longer.

A job can be Class 3 + Class 4 simultaneously (the basement above plus a hardwood floor on the upper-floor saturated through to the joists). Document both.

Wall-cavity inspection

The 24-inch threshold between Class 2 and Class 3 hinges on cavity moisture, not surface moisture. A wall that reads 12 percent at the painted surface 30 inches up might be hiding a saturated bottom plate behind the drywall. Use a borescope or probe-meter inspection at the base of each wall in the affected area. If cavity moisture is present above 24 inches, the job is Class 3 even if the drywall paper feels surface-dry.

Drill 1/4-inch inspection holes at 12, 24, and 36 inches above the floor on each affected wall, in the stud bays, and probe with a Delmhorst probe meter or a Tramex CMEX (concrete-moisture-meter, also functional in deep wall mode). Document holes in the file; they will be patched at end of project.

When the customer disagrees with the classification

Homeowners and adjusters sometimes push back on a Class 3 or Class 4 call because the higher class means more equipment-days and a larger invoice. The defense is the documentation: photographs of meter readings at the inspection holes, photographs of the saturated insulation pulled from a bay, the moisture-meter log. A clean inspection photo of the wet bottom plate at 30 inches up the wall ends the conversation.

If the homeowner declines the recommended scope and asks for a less-aggressive scope, document the recommendation, the homeowner's declination, and the reasonably foreseeable consequence (incomplete drying, secondary damage, possible mold). Have the homeowner sign the scope-decline. A scope-decline signed by the homeowner is not a waiver of all liability, but it is the strongest defense available against a downstream "you should have done more" claim.

Mixed-class projects

References

• ANSI/IICRC S500 Standard for Professional Water Damage Restoration, 4th Edition (2015), Section 10 (Inspections) and Section 12 (Restoration Procedures).
• IICRC Reference Guide for Professional Water Damage Restoration (2015), chapters on class and category determination.
• ASTM E2128 Standard Guide for Evaluating Water Leakage of Building Walls, applicable to wall-cavity inspection techniques.
• NADCA ACR 2021 Standard, for the threshold at which HVAC contamination becomes a separate-trade scope.