Perimeter drainage is the one part of a house that is judged entirely on what happens in November. A system that looks fine on a dry site can leave a basement wet the first week the Lower Mainland rains settle in, and the reason is almost never the pipe itself. It is grading, discharge and the details around them.
Start With Where The Water Goes
Before any pipe is laid, the question is where the collected water will end up. The options are a municipal storm connection, a sump with a pump, a rock pit, or a discharge to grade well away from the foundation. Each has rules attached to it, and each fails in a particular way if it is undersized. A rock pit in clay soil fills and stops draining. A sump without a backup fails with the power. A storm connection that was never camera-inspected may already be crushed at the property line.
Slope Is Not Optional
Perforated drain pipe has to fall continuously toward the discharge point. A flat run holds water, silts up, and eventually stops working altogether. On a sloped lot the pipe follows the footing around the house and everything has to be worked out so the low point lands where the discharge actually is, which is not always where it is convenient to dig.
What Goes In The Trench
- Pipe bedded on clean drain rock, not on native soil or backfill.
- Rock carried up and around the pipe so water can reach it from every side.
- Filter fabric between the rock and the soil, so fines do not migrate in and clog the system over the years.
- Cleanouts at the corners, so the line can be flushed and camera-inspected later without digging.
- Foundation waterproofing checked and repaired while the wall is exposed, because it will not be exposed again for decades.
Then Grade The Yard
The ground around the house should fall away from the foundation, and downspouts should be tied into the storm system or carried well clear of the wall. A great deal of “perimeter drain failure” is simply roof water being delivered straight to the footing by a disconnected downspout.
When To Look At Yours
Damp basement corners, efflorescence on the concrete, a sump that runs constantly, or a house from before the 1980s that still has the original clay tile. A camera inspection through the cleanouts is the quickest way to know whether the system needs cleaning, repair or replacement.
Related: drainage and excavation · camera inspections
Related guides
- HD Camera Inspections: Seeing Inside Your Pipes
- Installation: Setting a 150lb Fireclay Sink
- Fall Checklist: Preventing Burst Hose Bibs
- Top 5 Mechanical Red Flags for Langley Buyers
