How to scope retaining wall drainage & subsoil systems before pricing
Drainage work starts with diagnosis. Note whether water appears during short storms or only after prolonged rain, whether it emerges through joints or at the toe, and whether the ground above directs roof or surface runoff toward the wall.
A subsoil pipe is only one part of the response. Filter aggregate, geotextile, inlet protection, outlet level and lawful discharge all affect whether water can leave the retained zone without washing fine soil away.
Start with a wet-weather sketch showing high points, low points, roof outlets and every place water becomes visible. Timing matters: a wall that wets immediately may face surface inflow, while delayed seepage can point to saturated retained soil or an upstream source.
Inspect the outlet before designing the inlet. The available fall, connection point and maintenance access determine whether a gravity system is practical. An outlet that is buried, undersized or discharges onto unstable ground can transfer rather than solve the problem.
Fine soil and tree roots can shorten drain life. Ask how geotextile is wrapped, how aggregate is kept clean during installation and where inspection or flushing access remains. Avoid a detail that becomes impossible to service once paving or planting is reinstated.
Existing wall movement should be assessed separately from the drainage trench. Relieving water may reduce pressure, but it does not automatically restore rotated posts, cracked masonry or a displaced footing. The quote should state whether structural repair is included or excluded.
Near a stormwater easement, obtain the current asset information and follow City Services requirements before excavating. Footings and new loads may need clearance from buried pipes even when the proposed drain itself seems shallow.
Close-out evidence should show the aggregate zone, fabric, pipe grade, connections and outlet before they are concealed. Keep a simple maintenance note with the property and inspect pits or visible discharge points after heavy rain.