Got water somewhere? Know your mold risk now.

Because nobody can honestly predict the exact hour mold will appear in your specific wall cavity. It depends on the species of spores already present, local temperature, airflow, and a dozen other variables. Tools that hand you a countdown ("mold in 38 hours") sound precise but aren't. The IICRC, the industry body that writes the restoration standards, frames water damage as a set of categories and classes, not a timer. We follow that model. A qualitative band is honest; a countdown is theater.

IICRC S520 is the Standard for Professional Mold Remediation published by the Institute of Inspection, Cleaning and Restoration Certification. It is the document every licensed mold remediator in North America is trained against. It defines how to categorize water intrusion (Category 1 through 3), classify the extent of damage, and assess whether a structure is safe to occupy during remediation. This tool uses the same factor list that a certified technician would weigh on site.

Yes, a lot. Porous materials like drywall, carpet pad, and fiberglass insulation soak water deep into their structure and hold it for days, which is why they score higher in this index. Semi-porous surfaces like bare wood framing fall in the middle. Non-porous surfaces like glazed tile, sealed concrete, and metal release water back into the air quickly if you give them airflow. Same amount of water, three different risk profiles.

Any time the result lands in the High or Immediate band, or the water source is flood or sewage, or the affected area is larger than about 10 square feet, or anyone in the home has respiratory symptoms. IICRC S520 says a non-professional should not attempt remediation on Category 3 water (sewage, flooding from ground water) at all. For gray and clean water on small footprints, a DIY dry-out with fans and a dehumidifier within the first 24 to 48 hours is reasonable, but the moment drywall or carpet stays wet past 48 hours, the calculus changes.