Visible indicators documented during inspection, access and visibility limitations, and when detailed evaluation by a qualified roofer is recommended. Particularly relevant for Montreal urban plexes and commercial buildings. Educational page — not a watertightness certification or legal advice.
The flat roof — technically a very-low-slope roof — is a typical feature of Montreal's urban housing stock. Pre-1960 duplexes, triplexes and plexes in the Plateau, Rosemont, Villeray, Verdun, Le Sud-Ouest, NDG, Hochelaga-Maisonneuve and Ville-Marie almost all have flat roofs with bituminous, elastomer, EPDM or TPO membranes. Commercial and mixed-use buildings — in Montreal and elsewhere (Laval, South Shore commercial areas) — also use this roof type. Unlike pitched roofs, a flat roof depends entirely on the watertightness of its membrane and the quality of its drainage to evacuate rainwater and snowmelt. An aging membrane, a clogged drain, or prolonged water accumulation can quickly lead to interior infiltration. During a visual inspection, we document observable indicators — within the limits of what is safely accessible.
Here are the indicators we document during a visual inspection. Each is a sign to investigate, not a guarantee of infiltration or imminent failure. Detailed evaluation of watertightness is the responsibility of a qualified roofer.
Water that does not drain and remains on the roof for more than 48 hours after rain. Indicates insufficient slope, undersized drains, or local settling. Accelerates membrane wear and increases infiltration risk.
Drains clogged by leaves, debris or ice, missing drain baskets, misaligned or rusted scuppers. Deficient drainage is one of the main causes of overload and infiltration.
Blisters (bubbles) on the membrane, surface or deep cracks, open seams between sheets, loss of granules on bituminous membranes, multiple cumulative patches or repairs. Visible indicators of covering age and wear.
Cracked or leaning parapets, displaced or rusted metal cap, failed flashings around chimneys, ventilation ducts or plumbing vents. Frequent vulnerability points for infiltration.
Brick spalling from freeze-thaw on parapets, eroded or missing mortar joints, efflorescence on the interior parapet face. On Montreal plexes, these points are frequently associated with top-floor infiltration.
Water rings, halos, peeling or discoloured paint on the top-floor ceiling, particularly around chimneys, ducts or corners. Consistent with recent or past infiltration — the exact cause often requires further investigation.
Important: these indicators document conditions observed at the time of inspection. A roof that appears in good visual condition may still have hidden defects under the membrane or within the insulation layers. A visual inspection does not confirm watertightness or remaining service life — detailed evaluation is the responsibility of a qualified roofer.
Our visual inspection follows the InterNACHI standard. For flat roofs specifically, access and visibility limitations are important to understand.
We recommend evaluation by a qualified roofer in the following situations, ideally before removing the conditions on the purchase offer.
Unlike many defects that affect all regions, flat roofs are concentrated in the urban housing stock — particularly Montreal plexes and commercial/mixed-use buildings. Single-family suburbs with pitched roofs are less concerned by the specific issues covered here.
The other regions we serve (North Shore, West Island, Laurentides, Lanaudière, Estrie/Mauricie) consist mainly of single-family properties with pitched roofs. Flat-roof issues there primarily concern commercial buildings or exceptional cases — case-by-case verification if relevant.
If the pre-purchase inspection reveals visible wear indicators 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 a roofer.
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