Excavate to firm ground, build a compacted Granular A pad, set the first course partly below grade, step each course back into the slope, and drain the wall with clear stone, non-woven fabric and a perforated pipe to daylight. In Ontario, walls over 1 m of exposed height next to public property or building access need a permit and an engineered design.
Key takeaways
Installing an armour stone retaining wall comes down to six steps: plan the wall and check whether it needs a permit, excavate to firm ground, build a compacted Granular A pad, set the first course partly below grade, stack each course stepped back into the slope, and drain the wall with clear stone, filter fabric and a perforated pipe that outlets to daylight. Most of the strength comes from the weight of the stone and that backward lean, but drainage decides how long it lasts.
Armour stone retaining walls are a popular choice in Midland, Penetanguishene and cottage country because the stone suits the Georgian Bay landscape and holds up to freeze-thaw. This guide walks through each step, what the Ontario Building Code says about taller walls, and where homeowners usually go wrong.
Benefits of Armour Stone Retaining Walls
Durability
Armour stone is known for its strength and longevity. These stones can withstand harsh weather conditions and heavy loads, making them ideal for retaining walls.
Aesthetic Appeal
The natural look of armour stone adds a timeless beauty to landscapes. Each stone is unique, providing a rustic and elegant appearance.
Erosion Control
Armour stone retaining walls effectively prevent soil erosion, especially on slopes, protecting your property and maintaining the integrity of your landscape.
Low Maintenance
Once installed, armour stone retaining walls require minimal maintenance. They are resistant to pests, rot, and do not need frequent repairs.
Planning Your Armour Stone Retaining Wall
Site Assessment
Evaluate the site where you plan to install the retaining wall. Consider factors like soil type, slope, drainage, and the height of the wall.
Design and Layout
Create a design plan for your retaining wall. Determine the length, height, and curvature of the wall. Mark the area using stakes and string to visualize the layout.
Obtaining Permits
Check local building codes and regulations before you start. Under the Ontario Building Code (Div. A, 1.3.1.1), a retaining wall with more than 1 m of exposed height that is next to public property, next to access to a building, or on private property where the public is admitted is a designated structure: it needs a building permit and an engineered design. Lower walls and walls in a private backyard may not need a building permit, but your municipality can still have zoning, site alteration or lot grading rules, and work near a shoreline can need conservation authority or provincial approval. Our guide to retaining wall permits in Ontario covers this in more detail.
Materials and Tools Needed
- Armour stone
- Granular A for the base pad
- Clear (washed) stone for drainage behind the wall
- Non-woven geotextile filter fabric
- Perforated drainage pipe
- Excavator or loader sized for the stone
- Shovel
- Wheelbarrow
- Level
- Mason's line
- Measuring tape
- Compactor (hand tamper or plate compactor)
Step-by-Step Installation Process
1. Preparing the Site
Excavation
Excavate the area where the retaining wall will be built. Dig a trench roughly twice as wide as the base stones and deep enough to hold the granular pad plus part of the first stone, typically 6–12 inches (150–300 mm) or more for taller walls. Remove topsoil, organic material and soft ground until you reach firm subsoil.
Levelling
Level the bottom of the trench using a hand tamper or plate compactor. Ensure the base is firm and even to provide a stable foundation for the wall.
Adding Base Material
Fill the trench with at least 4–6 inches (100–150 mm) of Granular A, more on soft ground or under taller walls, and compact it in lifts with a plate compactor. The pad should be wider than the base stone. Granular A is a crushed stone with fines (OPSS 1010) that compacts into a firm, level bed.
2. Laying the First Course
Positioning the First Stones
Place the first course of armour stones in the trench so each stone sits partly below finished grade. That embedment stops the toe of the wall from kicking out. Set each stone on its flattest face, level front to back or tipped slightly into the slope, and check alignment with a mason's line.
Backfilling
Line the excavation behind the wall with non-woven filter fabric against the native soil, then backfill directly behind the first course with clear stone. The fabric keeps soil from migrating into the stone; the clear stone lets water drain instead of building pressure.
Installing Drainage Pipe
Lay a perforated drainage pipe in the clear stone behind the base of the wall, with continuous fall to an outlet where water can daylight without undercutting the wall. This pipe prevents water buildup and reduces pressure on the wall.
3. Building Up the Wall
Staggering the Joints
As you lay additional courses of stones, stagger the joints between rows so no vertical joint runs through two courses. Step each course back slightly from the one below. That backward lean, called the batter, puts each stone's weight behind the stone beneath it and is what lets a dry-stacked wall hold the slope.
Field drawing 10 · Armour stone
Armour stone walls hold by weight and setback
Each course leans back into the slope and sits on the one below. Drainage still matters.
Swipe to see the full drawing →
- Compacted granular pad. Granular A, compacted, wider than the base stone. Soft ground gets dug out first.
- Embed the base stone. The first course sits partly below grade so it can't kick out at the toe.
- Step each course back. The batter puts each stone's weight behind the one below. Set stones on their flattest faces.
- Clear stone behind. Free-draining stone in the joints and behind the wall relieves water pressure.
- Drain to daylight. A perforated pipe at the base, outletting where water can't undercut the wall.
- Fabric against the soil. Non-woven fabric between drainage stone and native soil. Walls over 1 m next to public areas need a permit and an engineer.
The drawing shows how the pieces work together: a compacted pad, an embedded base stone, each course stepped back, clear stone and a drain behind, and fabric between the drainage stone and the native soil. Stone sizes vary by quarry and wall height, so the exact setback and base depth are set on site or, for walls over 1 m in the situations the Building Code covers, by the engineer.
Maintaining Level and Alignment
Continuously check that each stone is level and aligned with the previous course. Use small pieces of gravel to adjust and level stones if necessary.
Backfilling
Backfill with clear stone behind each course as it goes up, keeping the filter fabric between the stone and the native soil. Fill gaps between stones with smaller stone so the courses lock together.
4. Closing the Filter Fabric
Wrapping the Drainage Stone
Once the wall is near full height, fold the non-woven filter fabric over the top of the clear stone so the drainage zone is wrapped on the soil side and the top. This keeps soil from clogging the drainage stone while letting water through.
Securing the Fabric
Secure the fabric in place with stakes or by tucking it behind the stones. Make sure it separates the drainage stone from soil everywhere.
5. Finalizing the Wall
Capping Stones
If desired, add a final course of capping stones for a finished look. These stones should be larger and flatter, providing a smooth top surface.
Backfilling with Soil
Finish the top 150–300 mm behind the wall with topsoil over the fabric, graded to shed surface water away from the top of the wall rather than toward it. Compact lightly to reduce settling.
Finishing Touches
Inspect the wall for any gaps or uneven stones. Make final adjustments to ensure the wall is stable and visually appealing.
Maintenance Tips
Regular Inspections
Inspect the wall periodically for signs of movement, erosion, or damage. Address any issues promptly to maintain the wall's integrity.
Weed Control
Keep the area around the wall free from weeds. Use mulch or ground cover to reduce weed growth and maintain a clean appearance.
Drainage Maintenance
Ensure the drainage system remains clear and functional. Check for blockages in the drainage pipe and remove any debris.
Soil and Plant Management
Manage the soil and plants around the wall to prevent excessive moisture buildup. Avoid planting large trees or shrubs close to the wall as their roots can cause damage.
Planning a 2027 armour stone retaining wall
If you want an armour stone retaining wall built in 2027, use the winter to settle the design and the paperwork. Decide on the wall's height, length and location, and find out early whether it will be over 1 m of exposed height in a spot where the Building Code requires a permit and an engineered design; engineering and permit review both take time. If the wall is near a shoreline or in a regulated area, ask your municipality and conservation authority what approvals apply.
Stone selection is the other winter job. Quarries and stone yards have different colours, sizes and finishes, and choosing early lets you match stone to the house and confirm delivery access for heavy trucks. Around Midland and Penetanguishene, excavation usually starts once the ground thaws and firms up in late April or May, and spring slots for machine work fill first.
- Measure the slope and the height the wall needs to retain.
- Confirm permit and engineering needs for walls over 1 m.
- Choose stone and confirm truck and machine access.
- Plan drainage and where the pipe will outlet.
FAQs
What is the best base material for an armour stone retaining wall?
Compacted Granular A is the usual base for an armour stone wall in Ontario. It compacts into a firm, level pad. Clear stone is used behind the wall for drainage, not under it.
How do I ensure my armour stone retaining wall is level?
Use a level and adjust each stone as you lay it. You can also use small pieces of gravel to shim and level stones.
Do I need a permit to build an armour stone retaining wall?
Under the Ontario Building Code, a retaining wall over 1 m of exposed height next to public property, next to access to a building, or on private property where the public is admitted needs a building permit and an engineered design. Lower walls may still fall under municipal or shoreline rules, so check with your local building department.
What is the purpose of landscape fabric in a retaining wall?
Landscape fabric prevents soil from clogging the drainage system while allowing water to pass through, reducing pressure on the wall.
How do I maintain the drainage system in my retaining wall?
Regularly inspect the drainage pipe for blockages and remove any debris. Ensure the landscape fabric is intact and not clogged with soil.
Can I build an armour stone retaining wall myself?
Only small walls. Armour stone is cut from quarried blocks, and typical wall stones weigh hundreds of kilograms to well over a tonne, so even a short wall needs an excavator or loader and an operator who can set stone precisely. Most homeowners hire an installer for anything beyond a single course of small stones.
How long does an armour stone retaining wall last?
A well-built armour stone wall on a compacted base with working drainage can last for decades. Failures usually trace back to a soft base, no batter, or water trapped behind the wall.
How much does an armour stone retaining wall cost?
Cost depends on stone size, wall height and length, site access and whether engineering is needed. See our guide to armour stone landscaping costs for typical ranges.
Building a wall that lasts
A good armour stone wall depends on a firm base, an embedded first course, a steady batter and drainage that keeps water from building up behind it. Get those right and the wall will hold its slope and its looks for a long time. For walls near water, see our waterfront retaining wall installation service.
Curious about the full range of ways to use armour stone on your property? Explore our armour stone landscaping ideas for creative inspiration beyond retaining walls.
We coordinate the P.Eng. stamp and the permit.
One team draws the site plan, commissions the engineering and builds the wall.
Forty-Five Scapes did a fantastic job replacing the broken concrete retaining wall at the end of our driveway with beautiful armour stone. They were punctual, worked long/hard days and finished the job extremely quickly. We couldn't have asked for better service!
Frequently asked questions
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