A dry stone retaining wall — built without mortar — relies on gravity, the friction between stone faces, and careful batter to hold back soil. In Canadian conditions, where frost penetrates between 0.8 and 1.5 metres depending on the province, correct base depth and drainage behind the wall determine whether it survives five winters or fifty.

This article covers the construction sequence from trench preparation through to the coping course, with specific attention to the details that most often cause failure in Canadian climates.

Note: Retaining walls over 1.0 metre in height typically require a building permit in most Canadian municipalities. Confirm requirements with your local building authority before construction.

Understanding Batter and Why It Matters

Batter is the backward lean of the wall face — the degree to which the face tilts into the hillside rather than standing perfectly vertical. A wall with no batter is fighting gravity with only friction; a wall with 1:6 batter (roughly 10 degrees from vertical) transfers soil pressure downward through the stone mass rather than outward through the face.

For walls up to 1.0 metre, a batter of 25 to 50 mm per 300 mm of height is a commonly cited starting point. Taller walls, or walls retaining saturated clay soils, generally require more batter. A simple batter gauge — a length of lumber with a plumb bob hung from the top at a calculated offset — keeps each course consistently angled during construction.

Site Assessment and Soil Conditions

Before any stones are moved, the retained soil type matters. Sandy or gravelly soils drain freely, reduce hydrostatic pressure, and are the most forgiving behind a stone wall. Clay soils hold water and expand during freeze-thaw cycles, which generates the lateral force that most commonly causes wall failure.

If the retained area is predominantly clay, plan for a more generous drainage aggregate layer (see below) and consider whether a mortar wall or a geogrid-reinforced block system might be more appropriate for the load. Dry stone walls are excellent for many applications, but they have limits when clay soil and water combine.

Trench Preparation and Base Course

The trench should extend below the local frost depth — at minimum 0.9 metres in most of Ontario, deeper in northern regions. A 150 mm layer of compacted crushed stone at the trench bottom creates a stable, draining base that resists frost heave beneath the wall.

The base course stones are the heaviest and widest in the wall. They are set to span the full wall width, buried below grade, with their flattest faces down. A level base course is the most important part of the build; any misalignment here compounds in every subsequent course.

Base Course Checklist

  • Trench depth to or below local frost line
  • 150 mm compacted crushed stone base
  • Largest available stones placed first
  • Flattest face down, widest face spanning full wall width
  • Top of base course checked for level across the run

Drainage Aggregate Behind the Wall

A 300 mm layer of 19 mm clear crushed stone — placed between the back face of the wall and the retained soil — intercepts groundwater before it can build pressure against the wall. The aggregate should extend from the base course to within 300 mm of the top of the wall, where a geotextile fabric layer separates it from the finish soil.

Without this drainage berm, water saturates the soil behind the wall during spring snowmelt and rain events. The resulting pressure is the most common cause of outward wall movement in the Canadian spring thaw period.

Building Courses

Each course above the base follows the same principle: no two vertical joints should align between adjacent courses. This bond — where each stone bridges the joint below it — is what gives the wall structural integrity. A wall built with running vertical joints (where joints line up course to course) will split apart along those lines under lateral pressure.

Throughstones — long flat stones that extend from the face into the fill — should be placed every 0.5 to 1.0 metres of length, at approximately every third course. They tie the face to the body of the wall and significantly increase stability.

Course Building Principles

  • Stagger all vertical joints — no two should align
  • Set each stone so it rocks as little as possible (use stone chips to stabilize if needed)
  • Place throughstones every 0.5 to 1.0 m along the run
  • Maintain consistent batter using a batter gauge on each course
  • Tighten larger gaps in the fill side with small stone fragments

Coping Course

The top course — called the coping — covers the wall's full width, ties the final course together, and sheds water away from the wall core. Coping stones are typically the flattest available, set slightly forward of the wall face to direct runoff outward rather than into the fill.

A well-fitted coping adds visual finish to the wall and reduces the amount of water entering the fill from above. In areas with significant soil above the wall top, a clay cap behind the coping can further deflect surface water.

Common Failure Patterns

Most dry stone wall failures in Canada follow one of three patterns: frost heave from an insufficiently deep base; outward bulging from hydrostatic pressure behind the wall due to absent or blocked drainage; or face delamination where the outer stones separate from the wall body because throughstones were omitted or spaced too far apart.

All three are preventable at the construction stage. Remediation after failure — which typically means dismantling the wall, correcting the underlying issue, and rebuilding — costs substantially more than getting those details right the first time.

References

Last updated: May 2, 2026