Stone Retaining Walls in Canadian Landscapes

A stone retaining wall holds back soil on a sloped site while providing a structured edge to a garden or yard. In Canada, retaining walls serve an additional function: they define planting terraces that allow gardeners to grow plants in well-drained raised beds above native soil that may be heavy clay or rocky. The combination of structural need and aesthetic opportunity makes them one of the most common stone landscaping projects.

Natural stone retaining wall. Photo: Wikimedia Commons (CC BY-SA 3.0)

When a Permit Is Required

In most Canadian jurisdictions, a retaining wall over a certain height requires a building permit. The threshold varies by municipality, but a common rule is that walls retaining more than 600–1000 mm (roughly 24–40 inches) of soil require engineering review and a permit.

Examples of current thresholds:

• City of Vancouver: Retaining walls over 1.2 m (approximately 4 feet) in height require a permit and structural drawings from an engineer. Source: City of Vancouver — Retaining Walls
• City of Toronto: Walls over 1 m that are adjacent to a property line typically require a permit. Always confirm with Toronto Building at toronto.ca
• Calgary: Development permits are generally required for walls over 1.2 m. Check calgary.ca/planning for current rules

For walls under the permit threshold — typically low decorative walls of 300–600 mm used to edge a garden bed — no formal approval is needed in most Canadian municipalities, though setback requirements from property lines still apply.

Dry-Stacked vs. Mortared Walls

The choice between a dry-stacked and a mortared wall has significant implications for drainage, maintenance, and structural behaviour in Canadian freeze-thaw conditions.

Dry-Stacked Stone

Dry-stacked walls use no mortar — stones are fitted tightly together and rely on gravity, weight, and interlocking placement for stability. Water passes freely through the gaps, which is a substantial advantage in Canada because hydrostatic pressure from saturated soil is a primary cause of wall failure.

Key characteristics of dry-stacked construction:

• Self-draining — water does not accumulate behind the wall
• Can accommodate minor frost movement without cracking
• Requires careful fitting and a slight backward lean (batter) into the slope — typically 25–50 mm of setback per 300 mm of height
• Individual stones can be replaced or re-fitted without demolishing the wall
• Practical height limit is roughly 600–900 mm without engineering input

Mortared Stone

Mortared walls use a cement-based mortar between courses. They present a cleaner face and can be built taller, but they require a poured concrete footing below the frost line — in most of Canada, this is 1.2–1.8 m depth depending on location.

• Requires concrete footing to prevent frost heave
• Must include weep holes every 1.2–1.5 m to drain water from behind the wall
• Mortar joints crack over time and require periodic repointing
• More suitable for higher walls or walls adjacent to structures

Layered stone retaining walls creating garden bed terraces. Photo: Wikimedia Commons (CC BY-SA 2.0)

Drainage: The Most Important Detail

Inadequate drainage is the leading cause of retaining wall failure in Canadian gardens. Saturated soil behind a wall increases lateral pressure significantly — particularly when that water freezes and expands. A properly drained wall installation includes:

• Drainage aggregate: A 300–500 mm layer of clean crushed stone or washed gravel placed directly behind the wall in the excavation zone
• Filter fabric: Geotextile fabric between the drainage gravel and native soil to prevent fine particles from migrating into and clogging the gravel over time
• Outlet: A path for water to exit — either through the base of the wall (dry-stacked), through weep holes (mortared), or via a perforated drain pipe at the base of the gravel layer running to daylight

Stone Selection for Retaining Walls

Flat-bedded stones — those with at least two roughly parallel faces — stack and interlock more effectively than rounded boulders. Common choices for Canadian retaining wall construction:

Construction Sequence

For a standard low dry-stacked wall (under 600 mm) in a residential garden:

1. Mark the wall line and excavate to a base depth of 150–200 mm below grade
2. Level the base and compact it; add a 100 mm layer of crushed gravel and compact again
3. Place the first course of your largest, flattest stones into the gravel; check level front-to-back and side-to-side
4. Backfill behind the first course with drainage gravel as you build up
5. Set each course with a slight backward lean (batter) and stagger vertical joints — no joint should run continuously through two courses (this is called a "running joint" and weakens the wall)
6. Use smaller stones as shims where needed to keep courses level
7. Cap the wall with your flattest stones, bedded in a thin layer of mortar if desired for stability

Seasonal Inspection and Maintenance

• Inspect the wall each spring after the ground thaws; note any bulging or leaning sections
• A wall that leans more than 25 mm out of plumb should be rebuilt — progressive leaning accelerates
• Clear weep holes in mortared walls each fall before freeze-up
• Repoint cracked mortar joints with a flexible, frost-resistant mortar (Type S or Type N)
• For dry-stacked walls, reset individual stones that have shifted outward; this is usually a straightforward repair

Further References

• City of Vancouver — Retaining Walls
• City of Toronto — Building Permits
• City of Calgary — Planning and Permits