Visible indicators compatible with ventilation problems documented during inspection (window condensation, attic frost, deficient hoods and fans, poorly maintained air exchanger, chronic humidity), limitations of visual inspection regarding ventilation performance and indoor air quality, and conditions favourable to mold development. Educational page — not a performance certification, not medical advice, not an indoor air quality diagnosis.
Buildings constructed since the 2000s are designed to be highly airtight — good for energy efficiency, but creating an active need for mechanical ventilation to remove humidity, CO₂, volatile organic compounds, and odours. When ventilation is insufficient, deficient, or poorly maintained, humidity accumulates, condensation appears on cold surfaces (windows, ducts, frame perimeters, basement floors, exterior attic ceilings), and conditions become favourable to mold development and material degradation. Older homes (pre-1980) are conversely often less airtight but with inadequate original ventilation (no bathroom fan, no air exchanger, unvented kitchen hood). During a visual inspection, we document visible indicators and risk conditions, without certifying system performance or diagnosing indoor air quality.
Here are the visible indicators we systematically document when ventilation or condensation problems are suspected. These indicators confirm neither definitive system failure nor indoor air quality — they guide toward complementary verification by a qualified specialist.
Beading, running, or frame icing on windows in winter, particularly in bedrooms and less-ventilated rooms. Indicator of high humidity and insufficient ventilation in the room — not a defect of the glazing itself.
Nail-head frost, humidity stains on insulation, visible condensation on roof sheathing in winter. Often due to deficient attic ventilation (blocked soffits, obstructed vents) or warm moist air leaking from the home into the attic.
Bathroom fan absent, present but non-operational, or vented into the attic rather than outside. Range hood recirculating (charcoal filter) instead of exhausting outdoors. These conditions concentrate humidity in the building envelope and promote condensation.
Dryer venting into the basement, attic, interior wall, or connected with a damaged duct. The dryer generates a large volume of water vapour and heat — its poor venting is a major source of humidity in the envelope.
No air exchanger in a recent airtight home, exchanger disconnected or broken, visibly clogged filters, blocked intakes and grilles. We note presence and apparent condition, without measuring performance.
Hygrometer reading >55-60% relative humidity on multiple occasions, humidity traces on cold surfaces (exterior walls, corners, window perimeters), finish warping, stains in less-ventilated zones. Conditions favourable to concealed mold development.
Important: these visible indicators document conditions observed at the time of inspection. A visual inspection does not certify ventilation performance, does not measure airflow rates, does not validate building-code compliance, and does not diagnose indoor air quality. Observed condensation is not synonymous with mold — it is a favourable condition. The absence of visible indicators does not guarantee adequate ventilation. Ventilation performance characterization is the responsibility of an HVAC specialist. Mold characterization is the responsibility of an industrial hygienist. We do not provide medical advice or remediation instructions.
Our visual inspection follows the InterNACHI standard. For ventilation and condensation, the limitations are important: the inspection documents visible indicators and risk conditions, not a performance measurement.
Our report documents visible indicators and risk conditions, and recommends, on a case-by-case basis, intervention by an HVAC specialist, certified energy evaluator, industrial hygienist, or healthcare professional based on the nature of observations.
Ventilation and condensation problems are found in all Greater Montreal regions — no area is exempt. Each region presents particular contexts that guide evaluation.
If the pre-purchase inspection reveals visible indicators compatible with a ventilation problem and the condition-removal deadline is short, several options are available depending on your risk tolerance and the seller's cooperation.
What is documented during an inspection, what is not, and when to consult an HVAC specialist or industrial hygienist.
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