A stone retaining wall holds back soil on a sloped site while allowing water to pass through its structure. Unlike poured concrete walls, stone construction — whether dry-stack or mortared — relies on mass and precise stone selection to resist the lateral pressure of retained earth. This article covers the principal steps involved in building a gravity-type stone retaining wall on a residential or small commercial site.
The guidance below is written for walls up to approximately 1.0 m (about 3.3 ft) in retained height. Walls taller than 1.0 m in most Canadian provinces require a stamped engineering drawing and may fall under municipal building permit requirements. Always confirm local regulations before breaking ground.
A gravity retaining wall assembled from cut stone blocks. Photo: Emadrazo, public domain via Wikimedia Commons.
Step 1 — Site Assessment and Layout
Before excavation begins, determine the wall's location, length, and the height of soil being retained. Drive stakes at each end and run a string line to mark the face of the wall. Note the existing grade on both sides; this determines how deep the base trench must go.
Check for underground utilities. In Canada, call Ontario One Call (if in Ontario) or the relevant provincial locate service before any digging. Most provinces have a free locate service that identifies buried gas, electrical, and telecommunications infrastructure within a few business days.
Rule of thumb for batter: A dry-stack stone wall typically leans into the slope at a rate of roughly 25 mm per 300 mm of height (about 1 inch for every foot). This backward lean — called batter — counteracts the tendency of retained soil to push the wall outward.
Step 2 — Excavation and Trench Preparation
Dig a trench along the layout line. The trench depth depends on frost penetration depth for your location:
| Region | Approximate Frost Depth | Typical Base Trench Depth |
|---|---|---|
| Southern Ontario / Lower BC | 600–900 mm | 300–450 mm below grade |
| Prairie provinces | 1,200–1,800 mm | 450–600 mm below grade |
| Northern regions | 1,800 mm+ | Requires engineering review |
For walls under 0.6 m retained height in temperate zones (e.g., coastal British Columbia), a 150–200 mm base trench with compacted aggregate is often sufficient. Colder inland locations warrant deeper preparation.
Step 3 — Drainage Layer
Poor drainage is the leading cause of retaining wall failure. Water that cannot escape accumulates behind the wall, increasing hydrostatic pressure to levels the stone mass cannot resist.
Place a minimum 150 mm layer of 19 mm clear crushed stone (sometimes called "clear stone" or "drainage stone") directly behind where the wall will sit. For walls over 600 mm in retained height, install a perforated pipe at the base of the drainage layer and daylight it at each end of the wall. Wrap the pipe in filter fabric to prevent fines from migrating into the aggregate.
Filter Fabric Placement
Geotextile filter fabric separates the native soil from the drainage aggregate. Lay it against the soil face of the excavation, drape it into the trench, and fold it back over the top of the drainage stone before backfilling. This prevents clay and silt particles from clogging the drainage layer over time.
Step 4 — Base Course
The base course is the most critical row of stone. It sits on the compacted aggregate bed and determines the alignment and level of the entire wall. Select the largest, flattest stones for this course. Dig each stone slightly into the aggregate so it sits firm with no rocking.
Check level along the run of the wall using a spirit level or laser level. The base course should be level side-to-side or slope very gently (no more than 25 mm per 3 m) toward one end to allow drainage water to exit. Any tilt in the base course is amplified by each subsequent layer.
A dry stone wall showing multi-course construction typical of traditional stone masonry. Photo: Kevin Rothwell via Geograph / Wikimedia Commons, CC BY-SA 2.0.
Step 5 — Building Courses
Work upward from the base course, staggering vertical joints between rows (running bond pattern). Each stone should bridge the joint below it — no vertical joint should align with the one in the course beneath. This interlocking is what gives dry-stack walls their lateral strength.
Tie Stones
At intervals of roughly 1.0 to 1.5 m along the wall, place a long "tie stone" that runs perpendicular to the face and extends well into the fill. These stones anchor the wall to the retained soil mass and are particularly important in walls over 600 mm tall.
Maintaining Batter
Use a batter gauge (a simple angled board or plumb bob offset) to maintain consistent backward lean as you build. Each course should set slightly further back than the one below it.
Step 6 — Capstones and Finishing
The top course, known as capstones, should be the flattest and heaviest available. They lock the wall together and shed water away from the wall core. Some builders set capstones in a small amount of mortar even on otherwise dry-stack walls, particularly in high-traffic areas where capstones might be dislodged.
Step 7 — Backfill
Backfill in lifts of 150–200 mm, tamping each layer before adding the next. Avoid using heavy plate compactors directly against the wall — the vibration can dislodge unfilled voids. Hand tamping or a light jumping jack compactor positioned at least 600 mm from the wall face is more appropriate.
Regarding permits: The National Building Code of Canada (NBC) does not itself issue permits — that responsibility falls to municipalities. A wall under 1.0 m retained height on private property in most municipalities does not require a permit, but rules vary. The City of Toronto, for instance, requires permits for certain retaining structures regardless of height when they adjoin a property line. Check with your local building department.
Common Errors to Avoid
- Skipping drainage — the most frequent cause of premature wall failure
- Using rounded river rock as primary structural material (poor surface contact between stones)
- Building too fast without allowing the fill to settle
- Placing the base course on undisturbed topsoil instead of compacted aggregate
- Ignoring frost depth requirements in the base trench
References: National Research Council Canada — National Building Code of Canada 2020; Ontario One Call (ontarioonecall.ca).