IICRC S520 Mold Remediation Standards

Reference Compliance Updated Aug 24, 2026 · Mold Remediation

Why this matters

The IICRC S520 standard is the industry guide for professional mold remediation. Insurance companies, attorneys, customers, and regulatory bodies all reference S520 when evaluating mold remediation work. A contractor performing mold remediation without S520 compliance is exposing themselves to legal and insurance liability; the work is harder to defend if it doesn't follow the standard. Knowing S520 is the foundational competency for mold remediation work.

What S520 covers

IICRC S520 (current edition 2024) is the "Standard for Professional Mold Remediation". It covers:

Inspection and assessment
Containment design
Personal protective equipment (PPE)
Engineering controls (negative air pressure, HEPA filtration)
Removal methods
Cleaning procedures
Verification of completion (post-remediation verification, PRV)
Documentation
Worker safety

The standard is voluntary in most jurisdictions but treated as the industry standard.

Key concepts

Condition levels

S520 categorizes contamination into Condition 1, 2, 3:

Condition 1: Normal fungal ecology; no remediation needed; cleaning may be needed
Condition 2: Settled spores or surface mold; can be cleaned
Condition 3: Actively growing mold (visible or hidden); remediation required

The condition determines the approach.

Containment levels

S520 defines three containment approaches:

Limited containment: small area; minimal containment
Full containment: standard professional containment
Full containment with negative pressure: more extensive; common for larger jobs

Categories of water damage

Per S500 (water damage standard, referenced by S520):

Category 1: Clean water (broken supply line)
Category 2: Gray water (dishwasher overflow)
Category 3: Black water (sewer backup; floodwater)

Categories 2 and 3 typically require mold consideration.

Standard remediation procedure (per S520)

Step 1: Inspection and assessment

Visual identification of moldy materials
Moisture readings
Identification of moisture source
Categorize contamination level (Condition 1, 2, 3)
Categorize affected materials
Document findings

Step 2: Containment design

Determine appropriate containment level
Plan containment perimeter
Plan HEPA filtration capacity
Plan negative pressure (if used)

Step 3: PPE

For mold remediation work:

N95 minimum (P100 preferred for heavy contamination)
Full body suit (Tyvek typical)
Disposable booties
Gloves
Eye protection
For Condition 3 in occupied areas: full face respirator

Step 4: Containment installation

Plastic barriers around the work area
Sealed at floors, walls, ceiling
Doorway through plastic with critical barrier or zipper door

Step 5: HEPA filtration

Air scrubbers with HEPA filters
Maintained negative pressure relative to surroundings
Discharge to outside if possible

Step 6: Removal

Remove moldy materials per the assessment
Drywall typically removed 2 ft beyond visible mold
Insulation typically replaced if affected
Carpet often removed and replaced if affected

Step 7: Cleaning

HEPA vacuum all surfaces
Damp wipe with appropriate cleaner
Repeat HEPA vacuum
May include encapsulant or biocide per assessment

Step 8: Drying

Verify any wet materials are dried to acceptable moisture levels
Document moisture readings

Step 9: Post-remediation verification (PRV)

Visual verification (no visible mold)
Moisture verification (within normal range)
Air sampling (optional but recommended)
Independent third-party verification (recommended for Condition 3)

Step 10: Build-back

Replace materials removed
Install new drywall, insulation, carpet as needed
Customer occupancy

Step 11: Documentation

S520 requires extensive documentation:

Pre-remediation assessment
Daily activity logs
Moisture readings
Containment setup photographs
PRV results
Final report

Categories of materials

Porous materials (typically replace)

Drywall (gypsum board)
Insulation (fiberglass, foam, cellulose)
Carpet and pad
Cardboard and paper materials
Particleboard

Semi-porous materials (sometimes replace)

Wood (consider species, condition, depth)
Stained or painted surfaces
Concrete (porous surface)

Non-porous materials (typically clean)

Glass
Metal (clean surface)
Tile (with grout)
Sealed wood

The decision to replace vs clean depends on:

Material type
Depth of contamination
Customer's preference
Cost

Specific S520 requirements

Personal protective equipment

For Condition 3 work:

Full body protection
Respirator (typically P100 or full face)
Disposable items used once
Wash hands and exposed skin after work

Engineering controls

For Condition 3 work:

Containment around the work area
HEPA filtration
Negative air pressure
Critical barriers at openings

Worker training

Initial training and certification (IICRC AMRT)
Periodic refresher
Site-specific training before each job

Documentation requirements

Comprehensive paper trail
Pre-remediation assessment
Daily logs
PRV results
Final report

When professional remediation is required

Per S520:

Condition 3 (active mold growth) requires professional remediation
Condition 2 with sensitive occupants (children, elderly, immunocompromised)
Condition 2 over a large area (typically over 10 sq ft)

For small Condition 1 or 2 in non-sensitive areas, homeowner DIY may be acceptable.

Insurance and S520

Insurance companies typically:

Require S520-compliant remediation
May require IICRC certification of the remediation contractor
May require third-party post-remediation verification
May limit coverage for mold (specific exclusions in many policies)

The contractor who follows S520 has documentation supporting the insurance claim.

Regulatory considerations

EPA has guidelines on mold (not enforceable per se)
OSHA general duty applies to worker safety
State / local: some have specific mold remediation laws (most don't)
IICRC S520 is the standard reference

Common S520 misunderstandings

"Bleach kills mold"

Bleach can kill some surface mold but:

Doesn't address the underlying issue
Doesn't penetrate porous surfaces
Sterilizes but doesn't remove
Not the right approach for professional remediation

"Spraying killed the mold"

Killing mold doesn't remove the contamination. Dead mold particles still cause health issues. Removal is part of the standard, not just killing.

"We don't need PRV; we can see it's clean"

A clean-looking work area is the start of verification, not the end of it. Three things a visual pass cannot tell you:

Settled particulate. Spores and hyphal fragments are not visible individually. A surface can look clean and still carry a loading that a tape lift or a swab picks up immediately.
Whether the moisture source is actually corrected. Materials read dry on the surface and hold water in the cavity, the sill plate, or the sheathing behind them. Without meter readings back in the normal range for that material and that building, the job will regrow.
Whether contamination escaped containment. Damage inside the work area gets cleaned because you can see it. Particulate that got past a torn barrier or an unsealed vent lands in rooms nobody inspected.

There is also a business reason. PRV is the record that the work met the standard on the day it was released. Without it, any later complaint (an occupant who feels unwell, a buyer's inspector who finds something in a wall, a carrier reviewing the claim) becomes your word against theirs, and the remediator with no verification documentation is the one who loses that argument. On larger or Condition 3 projects, an independent third party performing the verification removes the obvious conflict of interest in grading your own work.

The customer pushback is usually about cost or schedule. The honest framing: verification is a small fraction of the project, it is what closes the file, and skipping it means the project has no defensible end point. If the customer declines it anyway, put the declination in writing, signed, and note in the final report that the project was released without verification at the owner's direction.

References

IICRC S520 (Standard for Professional Mold Remediation, current edition).
IICRC AMRT (Applied Microbial Remediation Technician) certification.
IICRC AMRS (Applied Microbial Remediation Supervisor) certification.
EPA mold guidance documents.
OSHA general duty clause.
ANSI / IICRC S500 (Water Damage Restoration; companion standard).
Manuall internal: Universal Asbestos Lead Safety.