Visible drainage indicators, visual-inspection limitations since the drain is buried, and when a camera inspection or qualified drainage contractor becomes necessary. Educational page — not engineering expertise or legal advice.
A French drain is a perforated pipe installed around the foundation, below grade, generally wrapped in crushed stone and geotextile membrane. Its role is to collect groundwater before it exerts hydrostatic pressure against foundation walls, and to direct it toward a sump pit, ditch or storm sewer. In Quebec, a French drain typically has a service life of 30 to 50 years, depending on original materials (fibre, plastic, corrugated steel pipes), soil type, and environment (mature tree roots, iron ochre, sediment). A drain at end of life may be clogged by roots, cracked or crushed, or simply overwhelmed by an inflow of water exceeding its capacity. During a pre-purchase inspection, the drain itself is not visible — we document the visible drainage indicators and the exterior conditions that influence its performance.
Here are the visible indicators we systematically document during a pre-purchase inspection. Each is a sign to investigate, not a confirmation that the French drain is failing. Precise diagnosis requires specialist verification.
Moisture halos on foundation walls, elevated ambient humidity measured with a moisture meter, persistent musty odour. Several possible causes — the drain is one of them.
Whitish or crystalline deposits on interior or exterior foundation walls. Indicates water passing through concrete; suggests persistent hydrostatic pressure against the foundation.
Paint flaking, water marks, baseboard lifting along the junction between the foundation wall and basement slab. A common sign of water bypassing or overflowing the drain.
Lot sloped toward the foundation instead of away from it, standing water near the exterior wall after rain, sunken soil along foundations.
Downspouts discharging directly against the wall, disconnected or blocked gutters, missing splash blocks. Direct overload of perimeter drainage.
Window wells absent at basement windows, or window wells filled with soil, leaves, debris. A frequent entry point for rainwater that overloads local drainage.
Recent fill marks in the sump pit, undersized or old pump, absence of backup pump, absence of backwater valve. When the sump runs often, it is a sign that water is reaching the drain.
Gelatinous orange-reddish deposit visible at the accessible end of the drain, around the sump pit, or on exterior drain outlets. Particularly common on the South Shore and Île-Perrot. Iron ochre progressively clogs the drain.
Visible flood marks in the basement, repair remnants around the floor drain, waterline on boxes or items stored in the basement. A sign that drainage has been overwhelmed before.
Important: these visible indicators document conditions at the time of inspection. They do not confirm the actual state of the buried drain, which can only be evaluated by a camera inspection performed by a qualified drainage contractor. Several indicators may also have causes unrelated to the drain (condensation, internal leak, plumbing, gutters only).
Our visual inspection follows the InterNACHI standard. For the French drain specifically, the limitations are significant because the drain is buried.
We recommend a camera inspection by a qualified drainage contractor in the following situations, ideally before removing the conditions on the purchase offer.
The French drain exists in all regions, but the dominant issues vary by soil, construction period, and environment.
If the pre-purchase inspection reveals concerning visible 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 how to confirm the drain's actual condition.
Pre-purchase inspection in Greater Montreal. Report within 24h*. InterNACHI certified · IBC Network. Thousands of inspections.