A stone retaining wall performs two distinct functions simultaneously: it resists the lateral earth pressure pushing against its back face, and it presents a visual surface that reads as part of the residential landscape. Getting both right in a Canadian context requires careful attention to frost depth, drainage design, and stone selection — factors that are either absent or marginal in warmer-climate construction guides.
How Stone Retaining Walls Resist Earth Pressure
The simplest and most common residential retaining wall type is the gravity wall. As the name indicates, it resists the horizontal force of retained soil through its own mass. The wall relies on its weight, width, and the friction between its base and the underlying material to remain stable. No reinforcement, no tie-backs, no geosynthetic layers — just mass and geometry.
For a dry-stacked gravity wall to work, its width at the base must typically equal at least 50 to 60 percent of its exposed height. A wall retaining 900 mm of soil therefore needs a base at least 450 to 540 mm wide. This ratio increases as retained height grows, which is why stone gravity walls become impractical much above 1.2 to 1.5 metres without supplementary design measures.
Above that height range, provincial building authorities in most Canadian jurisdictions require either an engineered design or the substitution of a reinforced concrete structure with a stone-veneer facing. The threshold varies: Ontario and British Columbia generally apply engineering requirements at 1.2 m, while some Prairie jurisdictions use 1.0 m as the trigger. Homeowners should verify applicable local requirements before beginning work.
Stacked stone retaining walls creating level planting terraces. The battered face and broad base are characteristic of well-built gravity wall construction.
Frost Depth and Foundation Design
The most consequential Canadian-specific design factor for any retaining wall is frost depth. In most of Southern Ontario, frost penetration reaches 1.0 to 1.2 metres. In Edmonton and Saskatoon, design frost depths exceed 2.0 metres. A wall whose base sits above the frost line will experience upward heave each winter as the saturated soil beneath it freezes and expands, followed by settlement as it thaws — a cycle that progressively destabilizes the wall over years.
For walls retaining less than about 600 mm of soil, many experienced landscape contractors in Canadian markets simply set the base stone below the frost line and accept that this makes the foundation nearly as deep as the wall is tall. For taller walls with engineering requirements, a poured concrete footing keyed into undisturbed soil below the frost line is the standard approach.
Dry-stacked walls below 1.0 m in height in well-drained sandy soils can sometimes function without a below-frost footing if the base course sits on a compacted gravel bed at least 300 mm thick. The gravel dissipates frost heave by preventing moisture accumulation directly beneath the stone. This approach is common in cottage country across the Canadian Shield, where the shallow to bedrock conditions limit how deep a footing can be taken regardless of frost depth.
Drainage: The Critical Detail
Water pressure behind a retaining wall dramatically increases the load the structure must resist. A saturated soil exerts roughly twice the lateral pressure of the same soil in a dry condition. Hydrostatic pressure — water pressure alone — is additive to the soil pressure and can be the dominant force in a poorly drained installation.
Every stone retaining wall in a Canadian context requires a drainage system behind the back face. The standard approach combines a granular drainage layer — typically 200 to 300 mm of crushed stone or washed gravel — running the full height of the wall, with a perforated pipe at the base of the drainage layer that conveys collected water to a daylight outlet or a catch basin.
Filter fabric is placed at the soil-gravel interface to prevent fine particles from migrating into and clogging the drainage stone over time. This precaution is particularly relevant in glacial till soils common across much of Ontario, Quebec, and the Maritimes, where the particle size distribution includes a significant silt and clay fraction that can travel with water movement.
Mortared vs. Dry-Stacked Construction
Whether to mortar a stone retaining wall is one of the more consequential decisions in residential landscape construction. Each approach has specific applications where it performs well and others where it creates problems.
Dry-Stack Walls
In dry-stack construction, stones are laid without mortar, relying on weight, interlocking courses, and a battered (slightly backward-leaning) face to hold together. Dry-stack walls drain freely through their joints, which eliminates hydrostatic pressure almost entirely. They can tolerate minor differential movement from frost heave without cracking or displacing. And they can be dismantled and rebuilt if settlement occurs — a significant practical advantage over mortared work in areas with expansive or unstable soils.
The skill requirement for dry-stack is high. Each stone must be fitted to its neighbours in three dimensions, selecting pieces whose top surfaces bear level and whose face is presented cleanly. Corners and wall ends require particular care, as the interlocking pattern that provides stability in the field course is absent at the terminations.
Regional stone types commonly used for dry-stack retaining walls in Canada include Shield granite in Ontario and Quebec, Rundle quartzite in Alberta, and fieldstone sourced from agricultural land clearing across all Prairie provinces. The rougher the texture, the more face contact between stacked courses — which translates directly to friction resistance and stability.
Mortared Coursed Rubble
Mortared walls use Type S mortar bedded between courses to bind the structure. This approach is appropriate when the wall must meet specific fire ratings, when it is load-bearing in an architectural sense (a garden wall that also anchors a gate post, for example), or when the stone selected is too smooth or irregular to dry-stack reliably.
The disadvantage of mortaring a retaining wall is that the drainage capacity through the face is eliminated. Through-wall weep holes must be built into every mortared retaining wall at intervals of 1.0 to 1.5 metres along the base course to allow accumulated water to escape. Without them, hydrostatic pressure builds rapidly behind the wall and can cause sudden blowout — the entire face of the wall separating from the fill behind it under one heavy rainfall event.
Stone Selection for Retaining Wall Construction
The physical requirements for retaining wall stone differ from those for decorative cladding. Mass matters more than appearance, and durability in contact with soil and moisture is the primary criterion. Porous stones that absorb water and freeze — certain soft sandstones among them — degrade quickly in direct soil contact, where they remain saturated for long periods through spring thaw.
Granite, quartzite, and dense limestone are the three most commonly specified natural stone types for Canadian residential retaining walls. Each is widely available from Canadian quarries or regional stone yards, carries a good freeze-thaw durability record in the field, and can be supplied in the angular, roughly flat forms that stack reliably without excessive selection or cutting.
Updated: June 2026. For structural guidelines, see the Canadian Masonry Design Centre and the applicable edition of the National Building Code of Canada.