The five special signs under article 7.2.3 of the BNQ 3009-500 standard — iron ochre, pyrite and pyrrhotite, mold and microbial growth, asbestos, and rodents or other pests — are the ones the standard requires the inspector to pay particular attention to and flag to the requester when detected. The logic is threefold: health risk (mold, asbestos, rodent-borne contamination), structural risk (pyrite, pyrrhotite, carpenter ants, ochre clogging drains), and regional concentration in Quebec (each sign has a documented hotspot).
These are also the five categories most often litigated as hidden defects (vices cachés) in Quebec residential transactions. Recognizing them — or at least flagging the signs suggestive of their presence — is at the core of the inspector's work.
1. Iron ochre (ochre deposits)
What it is. Rust-colored gelatinous deposits formed when iron-rich groundwater reacts with oxygen and iron bacteria. Ochre progressively clogs the French drain and causes infiltrations and basement humidity.
Regional concentration. Montreal's North Crown (Laval, Lanaudière, Basses-Laurentides: Blainville, Terrebonne, Saint-Jérôme), Montérégie (notably the Saint-Jean-sur-Richelieu area), and parts of the St. Lawrence lowlands with iron-rich soils. Availability of specialized treatment services in a municipality is a good proxy indicator.
Signs to look for.
- Orange/rust-colored sludge at the sump pit or cleanout access
- Gelatinous deposits at the base of foundation walls
- Slow perimeter drainage after rain
- Persistent basement humidity or efflorescence
- Clogged or failed sump pump
- History of French drain cleaning (ask the seller)
What article 7.2.3 requires. Explicit mention in the report. If detected, recommend a camera inspection of the French drain by a specialized contractor.
2. Pyrite and pyrrhotite
What they are. Two iron sulfide minerals that swell by oxidation in the presence of moisture. Pyrite contaminates granular backfill under slabs (floor heaving, foundation wall cracking). Pyrrhotite contaminates the concrete itself (foundation disintegration from within).
Regional concentration.
- Pyrite: widespread across Greater Montreal, Rive-Nord, Rive-Sud, Laval. Traced to specific quarries whose backfill was distributed primarily across 1980s–1990s housing stock.
- Pyrrhotite: catastrophically concentrated in Mauricie and part of Centre-du-Québec, particularly in buildings constructed between 1996 and 2008. Municipalities eligible for the Société d'habitation du Québec compensation program include Trois-Rivières, Shawinigan, Bécancour, MRC Maskinongé, MRC des Chenaux, MRC Nicolet-Yamaska, and MRC Mékinac. The vast majority of cases are in Trois-Rivières.
Signs to look for.
- Star-shaped or map-pattern cracking on foundation walls (pyrrhotite)
- Slab heaving, gaps at door thresholds (pyrite)
- Horizontal cracks with rust staining in concrete
- Doors and windows progressively closing poorly
- Visible exfoliation or disintegration of the concrete surface (late-stage pyrrhotite)
- Buildings built in Mauricie between 1996 and 2008 (a red-flag worth mentioning even without visible damage)
What article 7.2.3 requires. Flag the sign. The inspector is not qualified to quantify the chemical composition — but must recommend the appropriate expertise: CTQ-M200 protocol for pyrite, petrographic core analysis for pyrrhotite. SHQ program eligibility rests on petrographic concrete analysis; for current thresholds and parameters, consult the SHQ pyrrhotite program page.
3. Mold and fungi
What it is. Fungal growth triggered by persistent excessive humidity in the building envelope, affecting indoor air quality and respiratory health.
Concentration. Not regional — per Quebec public-health data, mold and excessive humidity are a common problem in the housing stock, particularly in older under-ventilated homes, flat-roof buildings, and post-flood properties. Consult the INSPQ page on mold in buildings for current figures.
Signs to look for.
- Dark stains on walls, ceilings, baseboards, around windows
- Persistent earthy/musty smell in basements, closets, attics
- Damp drywall, bubbling paint, peeling wallpaper
- Water stains around bathtubs, under sinks, at window sills
- Condensation on windows (single-pane or failed double-pane)
- Elevated relative humidity (>50% sustained) on hygrometer check
What article 7.2.3 requires. Explicit mention. If detected, recommend expert analysis — BNQ 3009-600 is Quebec's dedicated mold-investigation standard.
4. Asbestos
What it is. Fibrous silicate mineral used as insulation, fireproofing, and filler in construction materials until regulated out in the late 1980s. Hazardous when disturbed: fibers become airborne and cause mesothelioma and asbestosis.
Concentration. Not regional — temporal. BNQ 3009-500 triggers on construction or renovations predating 1990.
Common asbestos-containing materials.
- Loose vermiculite attic insulation (Zonolite brand, Libby Montana mine, distributed in Canada until 1990)
- Textured / popcorn ceilings
- 9×9-inch floor tiles and their mastic
- Pipe and boiler insulation wrap (white, cloth-like)
- Cement-asbestos siding (transite)
- Plasters, joint compound, old HVAC duct tape
What article 7.2.3 requires. The inspector cannot visually confirm asbestos presence. They must flag suspect materials, inform the requester of the risk until lab analysis confirms absence, and identify precautions to take in the interim. Accredited-lab analysis typically runs $30 to $75 per sample.
5. Rodents, insects, pests
What it is. Any pest "likely to damage the components of the building", per the standard text — not aesthetic nuisance, but structural or electrical risk.
Regional concentration.
- Carpenter ants (Camponotus, black and red species): widespread across all Quebec regions; the dominant wood-damaging insect in the province.
- Termites: historically rare in Quebec, with localized and expanding pockets in parts of the southwest for over a decade. Documented service presence in Montreal and Laval. Phrase cautiously based on area.
- Mice and rats: present across Quebec, concentrated in older urban housing stock.
Signs to look for.
- Wood shavings (frass) near baseboards, window sills, attic beams — carpenter ant signature (termites, by contrast, leave no sawdust)
- Wood sounding hollow when tapped; soft or crumbling framing
- Mud tubes on foundation walls (termite signature)
- Swarmer wings on window sills in spring
- Rodent droppings in attics, basements, behind appliances
- Fibrous insulation used as nesting material
What article 7.2.3 requires. Mention any detected evidence of pest activity likely to damage components. Absence of detection should also be documented explicitly.
Why Axiom³ takes the five signs seriously
The Axiom³ report editor includes a dedicated block for each of the five signs under article 7.2.3. For each, the inspector marks detected, not detected, or not observable, and the final report explicitly accounts for all five. No more risk of forgetting one in a long report.
Try Axiom³ for free — 10 inspections, no credit card.
Sources & references
- BNQ 3009-500 — Residential Building (article 7.2.3): bnq.qc.ca
- ACQC — Iron ochre: acqc.ca/fr/ocre-ferreuse
- ACQC — Pyrite: acqc.ca/fr/pyrite
- Société d'habitation du Québec — Pyrrhotite program: habitation.gouv.qc.ca
- INSPQ — Mold in buildings: inspq.qc.ca
- BNQ 3009-600 — Mold standard: inspq.qc.ca
- CCOHS — Vermiculite and asbestos: ccohs.ca
- CNESST — Asbestos: cnesst.gouv.qc.ca
Last verified: April 22, 2026.