IICRC S520:2024 Mould Remediation — Assessment, Containment, Remediation & Clearance for Australian Technicians
IICRC S520:2024 — The Mould Remediation Standard
IICRC S520:2024 is the primary standard governing mould assessment and remediation in the restoration industry. It defines the roles of the Industrial Hygienist (IH), the Mould Remediation Contractor (MRC), and the project scope — from initial assessment through to final clearance testing. In Australia, IICRC S520 is referenced by insurers, hygienists, and restoration contractors as the baseline methodology for mould remediation claims. Understanding the four-stage process is essential for any technician working on jobs that involve mould growth or long-term water intrusion.
Stage 1: Assessment
The assessment phase is typically conducted by a qualified industrial hygienist, not the remediation contractor, to avoid a conflict of interest. The IH will: - Visually inspect the affected area and identify all areas of visible mould growth - Collect air samples (spore trap or culture) inside and outside the structure as a baseline - Collect surface samples (tape lift, swab, or bulk) from affected materials - Define the scope of remediation in a written remediation protocol The remediation contractor should not commence work without a written remediation protocol from the IH. On smaller jobs, some insurers allow the restoration contractor to conduct a visual assessment only and proceed under IICRC S520 limited or small-scale mould remediation guidelines.
Stage 2: Containment
Containment prevents the spread of mould spores to unaffected areas of the building during remediation. IICRC S520:2024 defines four containment levels based on the affected area: - **Limited containment**: <1 m² of mould growth; plastic sheeting over the work area, negative pressure maintained - **Full containment**: >1 m² and <10 m²; sealed work area with decontamination chamber, continuous negative air - **Medium and large scale containment**: >10 m²; engineered containment with HEPA-filtered negative air machines, full decontamination procedures Air movers must not be operated inside containment without HEPA filtration, as they would aerosolise and spread mould spores.
Stage 3: Remediation
Remediation involves the physical removal or treatment of mould-affected materials. Key principles under IICRC S520:2024: - Porous materials (drywall, insulation, carpet) with surface mould growth should generally be removed, not treated in place - Semi-porous materials (timber framing with surface mould) may be mechanically cleaned and treated with an EPA-registered antimicrobial - HEPA vacuuming before and after wet cleaning reduces airborne spore counts - Cleaning agents must be approved for mould remediation use — bleach is not recommended for porous surfaces as it does not penetrate to kill mould hyphae in the substrate All removed materials must be double-bagged in heavy-duty poly bags, sealed, and disposed of in accordance with local waste regulations.
Stage 4: Post-Remediation Verification (Clearance)
Post-remediation verification (PRV) is conducted by the IH after the contractor has completed remediation and BEFORE containment is taken down. The IH visually inspects for remaining visible mould, collects air and/or surface samples, and confirms that the remediated area meets the clearance criteria defined in the remediation protocol. Clearance criteria typically require indoor air sample counts to be at or below outdoor reference levels for the same fungi genera, with no visible mould remaining on remediated surfaces. Only after PRV clearance can containment be removed and the area cleared for reoccupation.
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