Retaining Wall Design in Burlington: Geotechnical Factors That Shape Every Project

Under the Ontario Building Code, any retaining wall exceeding 1.0 metre in height, measured from the bottom of the footing to the top of the stem, requires a building permit and must be designed by a professional engineer. Walls supporting a surcharge—such as a driveway, parking area, or adjacent foundation—require engineering regardless of height. Burlington's Building Services division enforces this threshold consistently, and a geotechnical investigation is typically required as part of the permit submission package.

The engineering design fee for a retaining wall in Burlington generally falls between CA$1,390 and CA$5,740, depending on the wall height, complexity of the ground conditions, and whether the scope includes just the design or also the construction review and field inspection during backfill placement. A simple cantilever wall under 2 metres on a single-family lot sits at the lower end, while a tied-back soldier pile wall with staged excavation monitoring moves toward the upper end of the range.

Drainage design for escarpment lots starts with the assumption that groundwater will perch on the Queenston shale contact. We specify a continuous 150 mm diameter perforated weeping tile at the base of the wall, bedded in 19 mm clear stone and wrapped in a non-woven geotextile filter fabric. The clear stone chimney drain extends to within 300 mm of the finished grade at the top of the wall. The outlet is daylighted at the low end of the wall or connected to a sump with a pump if positive drainage to the street is not achievable. This detail prevents the hydrostatic pressure that causes most residential wall failures in Burlington.

Yes, although Burlington falls into Seismic Category 1 under NBCC 2020—the lowest category—the code still requires a seismic check for walls classified as post-disaster structures or those with a high consequence of failure. The design ground motion is derived from the National Building Code seismic hazard tool for the specific postal code, typically resulting in a peak ground acceleration below 0.05g on firm ground. For most residential and commercial walls, the seismic earth pressure increment calculated using the Mononobe-Okabe method is small enough that the static design with adequate factors of safety governs. We include the seismic check in every design package for completeness and NBCC compliance.