A reference catalogue of defects frequently observed during building inspections across Greater Montreal. Designed to help buyers, owners and real estate agents understand what a visual inspection can — and cannot — detect, and when to consult a specialist.
This guide gathers the defects most frequently encountered during residential, multi-unit and commercial inspections in Greater Montreal. It is intended for buyers who want to understand what an inspection can reveal, owners who want to prioritize repairs, and real estate agents accompanying transactions. The content is informational only: it does not replace a building inspection performed on site, engineering expertise, a Phase I environmental assessment, legal advice regarding hidden defects, or a medical diagnosis related to air quality. For each defect, we indicate what is generally visible, the limits of a standard inspection, and when specialized verification is recommended.
Defects are grouped by category to reflect how a visual inspection is structured — from the exterior envelope to interior systems.
Foundation cracks, basement infiltration, end-of-life French drains, lot grading, high water table. The most expensive defects to repair often fall in this category.
Aging roofs, flat roofs with problematic membranes, deteriorated brick and joints, sagging lintels, failed flashing. First points of entry for water and heat loss.
Chronic humidity, insufficient ventilation, winter condensation, visible mold signs, indoor air quality. Visual inspection documents; environmental analysis is the specialist's domain.
Vermiculite possibly containing asbestos, lead or galvanized plumbing, knob-and-tube wiring, missing wall insulation. Particularities of the pre-1980 housing stock.
Federal Pioneer (Stab-Lok) panels, aluminum wiring, corroded cast iron drains, lead service lines, inadequate grounding. Visible conditions that warrant further verification.
Each defect listed below will receive a dedicated in-depth page. Current links point to relevant existing articles where available. Cards without a link correspond to dedicated pages in preparation.
Pyrite-contaminated backfill under concrete slabs, causing heaving, cracking and structural damage. Known concentrations in certain Laval, South Shore (Saint-Hubert, Brossard, Candiac) and North Shore (Mascouche, Boisbriand) developments built between 1985 and 1995. Confirmed by laboratory petrographic analysis.
Dedicated page →Humidity traces, efflorescence, paint flaking, musty odour. Possible causes: deficient exterior drainage, clogged French drain, foundation wall cracks, high water table. Identifying the exact source often requires follow-up during the wet season.
Dedicated page →Vertical, horizontal, stepped or diagonal cracks. Width, orientation and activity (active vs. stabilized) are documented. A wide horizontal crack may indicate active lateral soil pressure and warrant structural engineering expertise.
Dedicated page →Perimeter drain often at end of life after 50 years. Clogging by roots, iron ochre, or sediment. Visual inspection is limited to accessible ends; a camera inspection by a qualified drainage contractor is required to assess the drain's interior.
Dedicated page →Gelatinous orange-reddish deposit produced by bacteria feeding on iron in the soil. Clogs French drains and sump pumps, particularly on the South Shore and Île-Perrot. Visible at drain edges or via access to the sump pump pit.
Dedicated page →Elastomer, EPDM or TPO membranes at end of life. Wrinkles, blisters, ponding water, failed flashing around plumbing vents and ventilation ducts. Very common on Montreal and Laval plexes.
Dedicated page →Eroded mortar joints, brick spalling from freeze-thaw, rusted or sagging steel lintels over openings, vertical course displacement. Very common in pre-1950 Montreal triplexes and duplexes.
Dedicated page →Gold-brown granular insulation in pre-1990 attics, possibly contaminated with asbestos (Libby mine vermiculite, marketed under the Zonolite name). Visual identification by a trained inspector — confirmation requires sampling and laboratory analysis by a qualified specialist.
Dedicated page →Black, green, white, brown or pink staining on porous surfaces, persistent musty odour, chronic condensation, infiltration traces. Visual documentation only — species identification and health-effects assessment fall under the responsibility of an industrial hygienist or qualified healthcare professional.
Dedicated page →Modern airtight homes that are poorly ventilated, HRV/ERV units absent or unmaintained, excessive window condensation in winter, attic frost, chronic indoor humidity above 55-60%. Visible indicators and risk conditions documented; ventilation performance evaluated by HVAC specialist when required.
Dedicated page →Legacy-brand panels (Federal Pioneer Stab-Lok, Federal Pacific FPE, Commander, Sylvania/Zinsco, obsolete fuse panels), aluminum branch wiring (1965-1975) with concerns at terminations, visible signs of overheating or amateur modifications. Indicators visually documented; evaluation by a licensed electrician recommended — insurability may be affected depending on the case.
Dedicated page →Galvanized steel supply piping (internal corrosion, reduced flow) and cast-iron main drains (rust, flaking, localized perforations) in pre-1970 homes. Visible indicators documented at accessible points; internal condition assessed by camera inspection (separate service) or licensed plumber.
Dedicated page →A residential building inspection follows the InterNACHI standard and is limited to the visible and accessible condition of building components at the time of the visit. For each defect in the guide, we apply the same structure.
What we can observe, measure or photograph on site — cracks, stains, condensation, flow, humidity signs, protective devices present or absent.
What is not accessible (wall cavities, under-slab, internal drain, sealed ducts), what requires time (wet-season follow-up), or what exceeds our training (medical diagnosis, code compliance certification).
When a visual finding suggests a significant defect, we refer to a qualified specialist: engineer, certified technologist, industrial hygienist, drainage contractor, master electrician, real estate lawyer.
The report ranks findings by priority — to monitor, to verify, to correct before purchase, or to budget post-purchase. The goal is to inform your decision, not to make it for you.
The guide is a reference tool. An on-site inspection is the only way to document the actual condition of a specific property.
Some defects are more common in certain regions. Consult your area page for local particularities.
What this guide is, what it isn't, and how to use it.
Available 7 days a week in Greater Montreal. Report delivered within 24h*. InterNACHI certified · IBC Network. Thousands of inspections.