IICRC S520 Condition 1, 2, 3 Field Decision Tree

Why this matters

The S520 Condition classification drives every scope decision on a mold job: containment level, PPE, demolition extent, and clearance criteria. The three Conditions are not severity grades; they describe how the contamination got to a surface. A surface in Condition 3 must be cleaned or removed and verified. A surface in Condition 2 must be cleaned. A surface in Condition 1 is normal and is the target end-state. Misclassifying a Condition 2 wall as Condition 1 closes the job too soon and produces a callback. Misclassifying a Condition 2 wall as Condition 3 oversells demolition that was not necessary. This article gives the field decision tree.

The three conditions in plain language

Condition 1 (normal fungal ecology). The surface has only the ambient settled spore load found in any indoor space ventilated by outdoor air. Spore composition and concentration are comparable to local outdoor air. No visible growth, no source of contamination.

Condition 2 (settled spores). The surface has elevated settled spores from an indirect source: cross-contamination from an adjacent Condition 3 area, settled dust from prior remediation, or HVAC-distributed spores from a colonized cavity. No active growth on the surface itself. The colonization source is somewhere else; this surface only carries deposited spores.

Condition 3 (actual growth). Active fungal growth or settled spores from a known direct source on this surface. The hyphae are colonizing this substrate, or the source of contamination is in direct contact with this surface (a wet drywall paper face directly above a saturated bottom plate, for example).

The condition classification applies to each surface or material, not to the room as a whole. A room can contain Condition 3 drywall, Condition 2 contents, and Condition 1 framing simultaneously.

How to classify in the field

Use a structured assessment that combines visual inspection, moisture mapping, and where needed, surface and air sampling.

Visual indicators of Condition 3:

• Visible mold colony (hyphae, pigmentation, sporulation)
• Discoloration on a porous or semi-porous surface that has had documented water exposure beyond 72 hours
• Substrate paper or backing showing fungal growth visible only when the assembly is opened (cavity-side drywall paper, back of vinyl wallpaper, kraft facing on insulation)

Indicators of Condition 2:

• No visible growth on this surface, but a Condition 3 area is nearby and the air or surface has not yet been cleaned
• Surface dust film with elevated spore counts that match the Condition 3 spore species (use tape lift or direct microscopy from the lab)
• HVAC return air or supply boots downstream of a colonized AHU

Indicators of Condition 1:

• No visible growth, no documented water exposure within 72 hours, surrounding spore counts comparable to outdoor matched control
• Pre-existing clean surfaces in unaffected rooms with closed doors during the loss

Decision tree by material

Drywall, paper-faced. Look at both faces. Condition 3 if visible growth on either face. Condition 2 if no growth but the cavity is wet or adjacent material is Condition 3. Condition 1 if dry, no growth, no cross-contamination history.

Wood framing. Condition 3 only if visible growth or substrate has been wet beyond 14 days and surface microflora is visible under flash lighting. Wood framing without visible growth that has been dried below 16 percent MC on a Delmhorst BD-2100 (wood-equivalent scale) is typically Condition 2 at worst, cleanable in place.

Fiberglass insulation. Paper or kraft facing colonized: Condition 3 facing, dispose. Wet glass fiber without colonization: Condition 2 until dried. Glass fiber with growth on the fibers: Condition 3 batt, dispose.

Concrete and masonry. Surface efflorescence is not mold. Actual fungal growth on the surface from a chronic damp condition is Condition 3 surface; biomass can usually be cleaned to Condition 1 if the moisture source is corrected, because concrete does not support cavity-side colonization.

Carpet. Wet carpet beyond 48 hours with confirmed Category 2 or 3 water is Condition 3 per the combined S500/S520 framing - dispose. Dry carpet with surface dust from an adjacent Condition 3 area is Condition 2 - HEPA vacuum.

Contents. A book or photo album in the impact zone of a Condition 3 wall is Condition 2 (settled spores). The same book sitting in mold-colonized cardboard is Condition 3 (in direct contact with growth).

Decision tree by air sampling result

Air sampling supplements but does not replace visual classification. Use these comparisons:

• Indoor work area Asp/Pen counts greater than outdoor matched control by more than 2x, or different genus profile from outdoor: Condition 2 air in the work area, regardless of visible findings.
• Indoor sampled spore of a tertiary colonizer (Stachybotrys, Chaetomium, Fusarium) not present outdoors: Condition 3 air, look for the source. If not found visually, do a structural cavity inspection with thermal and borescope.
• Indoor work area counts and species comparable to outdoor matched control: consistent with Condition 1 air, but visual control still governs if growth is visible.

Scope decisions that follow condition

Condition 1 surfaces: leave alone. Do not include in containment unless they need protection from work being done elsewhere.

Condition 2 surfaces: clean. HEPA vacuum (HEPA-rated three-stage commercial vacuum, Nilfisk GM 80i, ProTeam ProForce 1500XP HEPA, or equivalent) followed by damp wipe with a registered antimicrobial. Replace HEPA filter media if pre-filter is loaded. For porous Condition 2 surfaces (drywall paint, fabric), assess whether cleaning will leave Condition 1 result; if not, treat as Condition 3.

Condition 3 surfaces: remove and dispose if porous (drywall, paper-faced gypsum, ceiling tile, carpet, raw wood with deep colonization). Clean and verify if non-porous (metal, glass, sealed surfaces, glazed tile). Semi-porous (sealed wood, vinyl, finished surfaces) is judged by depth of penetration; surface colonization with no deep invasion can be cleaned.

Verification by condition

Condition 1 target: visual clean, moisture content of underlying substrates within building-typical range (wood under 16 percent MC, gypsum at equilibrium with conditioned air), air sample showing genus profile comparable to outdoor matched control.

When all three are met across the materially affected area, the post-remediation verification passes per S520 Section 14 and the project moves to clearance documentation.

References

• ANSI/IICRC S520-2024 Standard and Reference Guide for Professional Mold Remediation, Section 3 (Principles), Section 10 (Inspection and Assessment), Section 12 (Remediation), and Section 14 (Post-Remediation Verification).
• EPA Mold Remediation in Schools and Commercial Buildings (EPA 402-K-01-001), Chapter 4 on Remediation Planning.
• AIHA Recognition, Evaluation, and Control of Indoor Mold (Green Book), Chapter 5 on Building Inspection.
• New York City Department of Health and Mental Hygiene, Guidelines on Assessment and Remediation of Fungi in Indoor Environments.