Block Retaining Wall

Our walls range from simple garden-bed borders under 600 mm that require only a well-compacted gravel base, up to engineered multi-tiered systems over 1.2 metres requiring geogrid soil reinforcement and engineered drainage schemes. Ontario's Building Code requires a building permit for retaining walls exceeding certain heights, and structural walls over 1.2 metres should be designed with input from a geotechnical or structural engineer. We work with a network of local engineers in our service area and can coordinate the engineering review as part of our installation process, so you're not chasing separate contractors.

A segmental retaining wall is only as stable as its base course, and the base course is only as stable as the material beneath it. Master Decker excavates a minimum of 150 mm below the finished grade for the base course, places a 150-mm layer of compacted clear stone, and verifies level across the full run before the first block is set. On clay-heavy soils — common across much of SW Ontario's agricultural belt — we excavate deeper and replace more of the native material with free-draining aggregate to reduce the seasonal moisture fluctuation beneath the base.

Drainage behind the wall is non-negotiable. We install a continuous 100-mm perforated drainage pipe at the base of the retained face, wrapped in filter fabric to prevent fines migration, connected to daylight at both ends of the wall. The drain core immediately behind the wall is backfilled with clear stone — not the native soil that retains water. This system routes hydrostatic pressure out of the wall rather than letting it build. It's not a complicated detail, but it's the detail that separates walls that last from walls that tip forward in year five.

Walls over 900 mm (approximately three standard block courses above grade, depending on the block system) require geogrid reinforcement to distribute retained-soil load across a larger mass rather than relying solely on the block weight and batter. Geogrid is a polymer mesh embedded horizontally into the retained soil at intervals specified by the block manufacturer's engineering tables — typically every three to four courses for walls in the 1.2- to 2.4-metre range. Master Decker follows Allan Block and Versa-Lok engineering guidelines precisely; grid length, vertical spacing, and connection method are not places to improvise.

Multi-tiered wall systems — stepped terraces on hillside lots or sloped rear yards — divide the total wall height into independent shorter walls offset by a minimum horizontal distance, reducing the engineering requirement per individual tier. These systems are visually striking and serve as integrated landscaping elements when planted between tiers. We design multi-tier layouts during the estimate phase, providing a sketch that shows finished grades, planting bed widths, and the step relationships between tiers before any excavation begins.

Not all segmental retaining block is equivalent. Big-box garden wall block is designed for low garden borders and lacks the batter angle, unit weight, and geogrid connection features needed for structural walls. Allan Block's Classic and AB Fieldstone series and Versa-Lok's Mosaic and Cobblestone systems are engineered products with documented bearing capacities, manufacturer engineering tables, and certifications that support permit applications. The visual range is substantial — rough-faced tumbled finishes for naturalistic settings, cut-face contemporary profiles for modern properties — and both manufacturers produce matching cap units that finish the top course cleanly.

Colour selection matters in Ontario's climate too. Darker block absorbs more heat and can accelerate ice formation at the cap course during freeze-thaw cycling. We advise clients on colour choices that balance aesthetic preference against long-term performance, and we source product that matches manufacturer specifications rather than substituting equivalent-looking block from a different supplier. Warranty coverage from Allan Block and Versa-Lok applies only when installation follows their documented procedures — another reason why cutting corners on base prep or geogrid placement voids more than just the workmanship guarantee.