French drain: how do you know whether it still works?

The French drain is the perforated pipe laid at the foot of the foundation, which collects groundwater and carries it to the sewer or a sump. It is buried, hence invisible: the inspector cannot judge its condition.

The signs are indirect (dampness, efflorescence, a busy pump, ochre deposits), and the only reliable examination is a camera inspection, done by a specialist from a cleanout port. Without a port, one must be created.

Fine sediment entering through the perforations, iron ochre in soils prone to it, roots, crushing, and for older houses, clay tiles that have shifted apart. A clogged drain goes unseen until water rises against the walls.

Cleanout ports, required by several municipalities for recent construction, change everything: they allow inspection and cleaning without excavation.

For a house over 25 to 30 years old with no port and no history, the drain’s condition is a major unknown, especially if the basement is finished. A camera inspection during the inspection condition is worth its price.

A working drain with ports and documented maintenance is a point in the house’s favour. An unknown drain is negotiated or provisioned for.

A camera inspection runs in the hundreds of dollars. Adding cleanout ports, a few thousand. Pressure cleaning, hundreds. Full replacement with excavation around the foundation, tens of thousands, plus landscaping to redo.

These are orders of magnitude. Confirm them with quotes.

Before you buy, here is what I would do.

1. Look for cleanout ports (often round covers in the basement floor or outside) and ask for the maintenance history.
2. Have the drain camera-inspected if the house is over 25 years old, if the basement is finished, or if the report notes signs of dampness.
3. Fix the grading and gutters first: a drain is not meant to take roof water.

I pick up every drain-related sign in your report, I separate finding from sign, and when the house profile warrants it, I put the camera inspection among the checks to do before lifting the condition.

Does your report mention this? Send it to me. In five minutes, I tell you what is priority, what to have checked and what to ask the seller.

Most houses built since the 1950s have one. Older ones may not, or may have a drain no longer in service.

No. The pump evacuates what the drain brings it. A pump that runs a lot indicates a drain at work, or a high water table.

Pressure cleaning and sometimes relining are possible depending on condition. A crushed or separated drain requires excavation.