Wooden Retaining Wall

Ontario winters stress retaining walls hard. Frost heave, hydrostatic pressure from snowmelt, and saturated soil in spring all push against a wall's structural capacity. A timber wall that's simply stacked in a trench without deadmen anchors, proper batter, drainage aggregate, and perforated drain pipe behind it will move within two to three seasons. Every wall we build is engineered for these conditions from the ground up.

The foundation is an excavated trench levelled to a compacted gravel base — the first course of timber is never laid on raw soil. We use No. 2 or better pressure-treated timber at CCA or ACQ ground-contact retention levels. Each course is spiked with rebar or timber screws, and deadmen anchors — horizontal members driven back into the hillside — are installed at intervals as the wall rises. Deadmen are the single most important element in a timber wall's long-term stability under lateral load.

Drainage is the other critical system. Behind every wall we lay crushed stone or drainage aggregate from the footing to near the top, and run slotted drain pipe at the base that daylights to either side of the wall or into a catch basin. This relieves hydrostatic pressure that builds behind walls during snowmelt and spring rain. Skipping drainage is why most DIY timber walls fail within five years. We don't skip it.

Residential timber walls are most commonly built with 6×6 or 8×8 pressure-treated posts or landscape timbers. Larger dimensions carry more lateral load and are used on taller or more heavily loaded walls. We specify ground-contact rated material throughout — UC4A or UC4B treatment depending on burial depth and local soil chemistry. Untreated or above-ground-rated lumber in a buried retaining wall application simply does not last, and we won't install it regardless of what a client may have seen at a big-box store.

Wall height is a key planning consideration. Timber walls under approximately 900 mm can typically be built without an engineer's letter, though local bylaws vary. Walls above 1.2 metres in many Ontario municipalities require either an engineer's stamp or a building permit. We'll confirm what's required in your municipality at the estimate stage and factor any permit requirements into the project plan so there are no surprises with the city after work is complete.

A retaining wall is only part of a grade-change solution. The usable space created above or below the wall is what drives the value. We look at how the grade change affects drainage away from the house foundation, whether terracing makes sense for multiple level changes, and how the wall integrates with adjacent patios, stairs, or fencing. We often combine timber retaining walls with pressure-treated stair runs and wood fencing to create a fully resolved backyard structure.

Planting can also play a role. Large shrubs or trees planted immediately uphill of a retaining wall add root-driven lateral pressure over time — a factor worth accounting for in the wall's design if your landscaping plans are ambitious. We'll talk through what you want the finished yard to look like so the wall is sized and positioned for the full picture, not just for the immediate grade change.