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Mold Water Restoration Process IICRC S500 

The IICRC-approved Applied Structural Drying (ASD) courses have been describing four classes of water for some time. However, the term is new to the S500. It is the “initial amount of water and the likely or anticipated rate of evaporation based upon the quantity and type of wet materials in the affected space.”

How Bad Is it? Really.

The four classes of water are:

  • Class 1 (least amount of water, absorption and evaporation): Water losses that affect only part of a room or area, or larger areas containing materials that have absorbed minimal moisture. Little or no wet carpet and/or cushion is present.
  • Class 2 (large amount of water, absorption and evaporation): Water losses that affect at least an entire room of carpet and cushion (pad). Water has wicked up walls less than 24 inches. There is moisture remaining in structural materials (e.g., plywood, particle board, structural wood, VCT, concrete. substructure soil).
  • Class 3 (greatest amount of water, absorption and evaporation): Water may have come from overhead. Ceilings, walls, insulation, carpet, cushion and subfloor in virtually the entire area are saturated.
  • Class 4 (Specialty drying situations): These consist of wet materials with very low permeance/porosity (e.g., hardwood, plaster, brick, concrete, light weight concrete and stone). These types of losses may require longer drying times and special methods.

Importance to perform an inspection and develop a preliminary determination as to the category of water that has caused the flooding issue. The preliminary determination is that the category of water is “1.” As part of the inspection we would also want to establish our drying goal and a written scope of work. In the S500, we have a “dry standard” and a “drying goal.” The dry standard is determined by taking moisture content (MC) readings from known dry materials in an undamaged area of structure (referred to as normal EMC). From the dry standard this can help establish the drying goal needed for a speedy revovery. We clarify a target moisture level within an acceptable proximity of the dry standard along with air samples in all areas of work. We also perform control samples to establish air quaility issues prio to loss.

Section it states: “…then properly dry exposed wood framing to within four percentage points of normal EMC. At a minimum, wood framing materials should be below 16% MC before installing new drywall.”

In order for drying to take place expeditiously, “It is recommended that consideration be given to whether demolishing or removing structural materials is appropriate in setting up the initial drying system.…Unrestorable structural components removed. Remove materials that slow down the drying process. (e.g., vinyl plank flooring, cabinets that cover wet drywall, carpet and padding over flooring).”

Excess water must be extracted, and the un-restorable materials removed. Category 1 water uses a closed drying system (i.e., not using outside air) and dehumidification. The most common class of water damage is Class 2. If there is contamination present, the drying environment requires further modification.

The IICRC S500 defines Category 2 water damage incidents as water that “contains significant contamination and has the potential to cause discomfort or sickness if contacted or consumed by humans.” We feel this is the most appropriate way to describe most property damage derived from water.

The IICRC S500 defines Category 3 water damage as water that is “grossly contaminated and can contain pathogenic, toxigenic, or other harmful agents and can cause significant adverse reactions to humans if contacted or consumed.” Examples of Category 3 water damage can include:

  • Sewage & wastewater line backup

  • Seawater

  • Rain from storms

Category 1. "Clean Water" is from a source that poses no substantial harm to people. Water that overflowed while running your bath water, leaking from a supply line for an ice maker, dishwasher or clothes washer are good examples. This assumes that the surfaces being flooded are reasonably clean. Flooding from clean water is usually treated by extracting standing water. Air movers are set up to create evaporation and dehumidifier's to remove the moisture from the air.  After 48 hours, a Category 1 can become a Category 2.

Category 2. "Grey Water" poses health risks due to significant levels of contamination of bacteria, mold and/or chemicals. This includes dirty water from washing machines, dishwashers, as well as leaks from water beds, broken aquariums and urine. The water restoration technician should wear some personal protection equipment (PPE). The carpet padding is usually removed and replaced because its sponge-like structure offers the perfect environment for bacterial and mold growth. Due to rampant bacterial breeding and mold growth, Category 2 becomes a Category 3 situation if left untreated for 2 days or more.

Category 3. "Black Water" contains disease-causing organisms, toxins, and is grossly unsanitary. Typical black water conditions occur from a sewer back flow, a broken toilet bowl containing feces, and rising flood waters. (Rising flood water is considered Category three because of the possibility of chemicals and organisms found in lawn chemicals, fertilizers, animal feces, decaying ground debris, and over filled sewer and septic systems.)
Tetanus and other serious diseases are likely to be present in rising flood waters. The water restoration technician must wear personal protection equipment. Affected objects such as carpet, padding, and Sheetrock must be removed and disposed. A biocide must be applied to kill micro-organisms on site.

Air Mover Use

Stop The Mold..Dry it Out! We install one air mover for each 10 to 16 linear feet of wall, with the outlet of each air mover pointing in the same direction. With the air mover almost touching the wall, aiming its outlet at the wall at a 12-to-45-degree angle. Also placing at least one air mover for each small bathroom, closet or other offset.

Example:  12-by-12-foot room (48 linear feet of wall space), it may be appropriate to use from 4 to 5 air movers (4 walls and a closet), depending on response time; the materials present; amount of water exposure; and atmospheric conditions. 

Air-moving devices inherently tend to aerosolize soils and contaminants. Restorers can install one or more air filtration devices, or AFDs, as air scrubbers, depending on the AFD’s size and obstructions within the structure. AFDs provide additional airflow, while simultaneously removing aerosolized soils or contaminants from the air within a room.

Our Movers save the day!

  • 1/5 hp, Energy Efficient Thermally Protected Motor with Powerful 1400 CFM ( not the cheap Home Store Models )
  • GFCI Protected for Fire Prevention

As air moves across a wet surface, evaporation of moisture into a drier air mass occurs. As this air becomes more humid, evaporation (drying) slows and secondary damage becomes a concern. It is also necessary to remove the added moisture from the interior air space.


Dehumidification is the removal of moisture from the air. Initially, effective drying of structural materials requires that air in a structure should be exchanged based on the dehumidifier’s ability to remove a specific number of pints per day. On-going equipment use is based on psychrometric calculations to verify adequate and safe drying.

Calculate the cubic footage of the room or area to be dried.

For example:

30’ x 50’ = 1500 sf x 8’ = 12,000 cf
12,000 cf divided by 50 (LGR/Class 2) = 240 pints at AHAM
If you are using LGRs rated at 65 pints = 4
If you are using LGRs rated at 140 pints = 2

We use SLGR Microchannel Technology is a revolutionary and innovative technology. The use of microchannel condenser technology can improve the 50% dispersion effect of the condenser, 30% of heat exchange area and 50% of the refrigerant quantity. When the SLGR microchannel is combined, the efficiency of the industrial dehumidifier can be increased by 30-50%.

Following and Exceeding The Standard

The IICRC S520 Standard describes the procedures to be followed and the precautions to be taken when performing mold remediation in residential, commercial, and institutional buildings, and the systems and personal property contents of those structures. The ANSI/IICRC S520 is a procedural standard for the remediation of mold damaged structures and contents. The ANSI/IICRC S520 is based on reliable remediation and restoration principles, research and practical experience, and attempts to combine essential academic principles with practical elements of water damage restoration for technicians facing “real-life” mold remediation challenges. 

The damaged structure is monitored starting with the initial loss assessment and evaluation and continuing throughout the restoration process. Technicians establish a moisture content or drying goal for affected building materials and contents items that is in the written scope of work.

Psychrometric conditions and MC measurements is recorded daily. Relevant moisture measurements include temperature and relative humidity both inside and outside of affected and unaffected areas, and at dehumidifier outlets. Section 12.1.25 of the Standard states that, “If moisture measurements do not confirm satisfactory drying, restorers should adjust drying procedures and equipment placement, or possibly add or change equipment to increase drying capability.”

The S500 does provide additional information on variety of related water-damage restoration subjects involving all categories and classes of water. The use of open drying systems and hot air drying systems are also discussed.

For more information, contact the IICRC at


Water Damage and Mold in Seattle, Bellevue, Kirkland, Redmond, Renton, Kent & Issaquah. Work with us! We are local Water Mold Restoration Co. not National Insurance Work Chasers! 425.608.9553