Category is how contaminated the water is, on a scale of one to three. Class is how much material got wet and how hard it will be to dry, on a scale of one to four. Those two numbers come from ANSI/IICRC S500, the water damage restoration standard, and they decide almost everything that happens next in your house: which materials are dried where they lie, which ones are cut out and carried to the truck, how many air movers stand in the room, and what the insurance file has to show.
Most homeowners meet these numbers for the first time on the worst morning of their year, written on a form by somebody they met ten minutes ago. Knowing them in advance turns the assessment into something you can follow instead of something that happens to you.
Category one, two and three: how dirty the water is
S500 sorts water by what is in it at the moment it reaches the material, and the category can climb while you wait.
| Category | What it is | What it usually means for materials |
|---|---|---|
| Category 1 | Clean and sanitary water, from a supply line or a similar clean source. | Often dried in place if it is reached quickly. |
| Category 2 | Gray water carrying contamination that can cause illness, from an appliance or an overflow. | The carpet pad and wet drywall usually come out. |
| Category 3 | Grossly contaminated water, including sewage and floodwater from the ground. | Porous materials that the water touched are removed and discarded. |
Two consequences of that table are worth saying plainly. The first is that clean water does not stay clean. Water sitting on a floor picks up soil, dyes, adhesives and whatever the carpet has held for years, and time and temperature move a category one loss toward category two. The second is that a category is assigned to the water where it is now, not to the pipe it came out of. A clean supply line that has been running behind a wall for two days is no longer a category one job in that wall.
Ground water and surface flooding are category three from the first minute, because of what a river or a street drain carries.
Class one, two, three and four: how much is wet
Category describes the health problem and class describes the drying problem. Since the fourth edition of S500 in 2015, class counts the evaporation load: how much of the combined floor, wall and ceiling surface area is wet porous material, and how much water is bound inside materials that give it up slowly.
- Class 1 is the smallest evaporation load. Wet porous material covers less than about 5 percent of the combined floor, wall and ceiling surface area, with little absorption into low evaporation materials.
- Class 2 is roughly 5 to 40 percent of that combined surface area in wet porous material, so there is far more water to evaporate and the room needs proportionately more air and dehumidification.
- Class 3 is more than about 40 percent of the combined floor, wall and ceiling surface area, which is the largest ordinary evaporation load a house produces.
- Class 4 is specialty drying, where a significant amount of water is bound inside low evaporation materials or assemblies such as plaster, wood, concrete, masonry and multilayer subfloors, which need longer drying or special methods.
Class is why two jobs with the same puddle can need very different equipment. A category one supply line leak across a tiled kitchen floor is a small class 1 problem. The same volume of water under a strip oak floor is a class 4 problem that will hold drying equipment for days, and it is the reason a technician cares about what the floor is made of before caring about how big the puddle looks.
What the two numbers decide together
Category decides what stays and what goes. Class decides how much equipment stands in the room and for how long.
On a category one loss reached in time, carpet is commonly dried in place with the pad left down, air movers set to move air across the surface and a dehumidifier taking the water out of the air. On a category two loss, the pad is a sponge that has held contaminated water against the subfloor, so the pad comes out and usually the lower part of the wet drywall with it. On a category three loss, the porous materials the water touched are removed and discarded before anything is dried, because drying contamination in place leaves the contamination in the house.
This is the reason nobody can tell you on the phone whether your carpet will be saved. The answer is a function of the category, the class, the material and the hours that have passed. What a technician can tell you on the phone is what would have to be true for it to be saved.
Where the numbers show up in your insurance file
The category and the class are written into the file at the start of the job, and everything after them is measured against them. S500 asks for the drying process to be documented with psychrometric readings taken at each monitoring point on each day the project is active: temperature, relative humidity, specific humidity and grain depression. Photographs are expected to show the moisture meter reading and the affected material in the same frame, so the reading can be checked without taking the written log on trust.
An adjuster reading a file with a category three assessment and no removal of porous material is reading a contradiction, and so is a file that claims a week of drying on a class 1 loss. The numbers are what make the rest of the file legible. This is also why the readings are logged daily and not written up at the end from memory.
DHL documents the loss with photographs and moisture readings, so you have a complete file to give your insurer. The business does not file, adjust or negotiate the claim, because that is regulated work and it belongs to you and your carrier.
The questions to ask on the day
You do not need to run the assessment. You need to be able to follow it, and four questions are enough.
- What category is this water, and what made it that category?
- What class is the loss, and which materials put it there?
- Which materials are being dried in place and which are coming out, and why?
- Where are the monitoring points, and when do I see the readings?
A technician who can answer those four in plain words is running the job to the standard. A technician who cannot is guessing, and a guess is expensive later, when the floor cups or the wall smells in November.
What DHL does with the numbers
The assessment happens before extraction. A category and a class are set, moisture is mapped, extraction runs at any hour, equipment is placed to suit the class, and readings are taken at set points each day until they hold at a dry standard. Those readings end the job, and no set number of days does: hardwood, plaster and concrete take longer than carpet because they release water slowly. The full method for the work is on the Water Damage Restoration page, and the same team covers Passaic County and the five other counties.
A written estimate comes before any work begins, with no hidden fees, and the estimate itself is free.
This article is about Water Damage Restoration.