Mold remediation is the professional process of assessing a building for indoor fungal amplification, controlling the moisture that produced it, containing the work so the rest of the structure stays at a normal fungal ecology, removing or cleaning contaminated materials, and verifying that the space is ready to rebuild. In the United States the governing technical reference is the ANSI/IICRC S520 Standard for Professional Mold Remediation. When the building is still wet, ANSI/IICRC S500 still governs extraction and drying. You do not get to pick one standard and ignore the other.
Mold is not a stain. Spores, fragments, and settled dust move with air, on tools, and on clothing. A scope that skips the moisture source, skips containment, or treats a spray-and-wipe as remediation is not S520 work. The clock that matters on a water-origin job is the moisture clock: indoor amplification after a wetting event is commonly discussed in the 24-to-48-hour range. That is why extraction and drying sit in front of any mold conversation that started as a Category 1 or Category 2 loss. Once visible growth or a Condition 3 reservoir is present, S520 is in play whether or not anyone has a lab report in hand.
What ANSI/IICRC S520 requires
S520 is the standard of care for professional mold remediation. It is not a logo for the truck and it is not a substitute for a work plan. The standard requires a competent assessment, identification and correction of the moisture source, a written work plan, engineering controls matched to the Condition, removal or cleaning decisions by material type, and post-remediation evaluation. A proposal that cannot name Condition, moisture source, containment, and verification is not an S520 plan. It is a price.
S520 uses Condition language. Condition 1 is a normal indoor fungal ecology — what you expect in a well-maintained, dry building. Condition 2 is settled spores, fragments, and fungal structures that originated from an indoor amplification site and landed on surfaces that may still look clean. Condition 3 is actual indoor amplification: visible growth, hidden growth in an assembly, or other evidence that fungi are growing indoors. Treating every stained ceiling tile as Condition 3, or every musty closet as “no mold,” both fail the standard. Assessment comes first. The Condition call is made by area, not by the address.