Retaining Walls in Ottawa — Built to Hold Through Every Frost Cycle
A retaining wall has one job: to hold back soil and manage grade change without shifting, cracking, or leaning over time. In Ottawa, where the ground freezes deep, and clay soil holds moisture through the thaw, that job is harder than it sounds. A wall that isn’t built with proper drainage behind it and proper footing depth below it will move. Maybe not the first year — but give it three or four freeze-thaw cycles, and it’ll tell you everything you need to know about how it was built.
Bennett Lawn & Landscape installs retaining walls in Ottawa and the surrounding area. We work in armourstone, interlocking concrete retaining systems, and natural stone, and every wall we build starts with the same foundation: proper drainage, proper depth, and the right material for the load it’s carrying.
What Kind of Retaining Wall Do You Need?
That depends on the grade change, the soil conditions, and what you want the finished space to look like. Here’s how we approach the main options:
Armourstone retaining walls
Armourstone, large natural granite or limestone boulders, is what we use for serious grade changes. It’s heavy, it interlocks naturally, and it handles lateral soil pressure better than most manufactured systems. You’ll see armourstone walls along roadsides and commercial properties because it’s genuinely the most robust option for high retaining applications. In residential settings, it also has a natural, rugged look that works well with gardens and sloped properties.
Interlocking concrete retaining wall systems
Products like Unilock Pisa2, Oaks Classic, and similar interlocking systems work well for medium-height retaining walls, typically under four feet, and allow for more precise shaping, curves, and finished aesthetics. They pair naturally with interlock patios and walkways and are a popular choice for front yard grade changes and tiered garden areas.
One thing worth knowing: most manufactured retaining systems have a specified maximum height before engineering is required. We follow those specs, and if your wall needs to be higher, we’ll tell you what’s required.
Natural flagstone and fieldstone
For lower decorative walls, garden borders, raised bed edges, and low terrace features, natural stone has a warmth and character you don’t get with manufactured products. These aren’t load-bearing in the same way, but they’re built with the same attention to base prep and drainage that everything else gets.
Why Retaining Walls in Ottawa Fail — and How We Prevent It
- No drainage behind the wall. Water that can’t escape builds up pressure behind the wall face. In freeze-thaw conditions, the trapped moisture expands and contracts repeatedly. Eventually, something gives. The fix is gravel backfill and, for taller walls, weeping tile at the base that directs water away from the structure.
- Footing too shallow. Ottawa’s frost depth is roughly 1.5 to 2 metres in a cold year. A wall base that doesn’t get below the frost level will heave. It doesn’t matter how well the face is built; if the base moves, the wall moves. We excavate to the proper depth every time, which takes longer and costs more in materials, but it is not optional.
We’ve repaired walls, some done by other contractors, some DIY, where neither of these things was addressed. The repairs are usually more expensive than building it right the first time.
Retaining Walls Combined with Other Landscaping
Retaining walls rarely stand alone in a project. Most of the wall installations we do are part of a larger yard redesign that includes:
- Tiered patios where the wall defines the change in level between two usable spaces
- Garden beds installed directly above or against the wall face
- Grading and drainage work to address the water movement that often causes grade issues in the first place
- Interlock steps connecting different levels
- Armourstone combined with decorative planting for a naturalized look
If your yard has a slope that makes it hard to use, a well-placed retaining wall, or a series of smaller walls, is usually the most durable way to solve it.
WHAT OUR CLIENTS SAY
Get a Quote for Your Retaining Wall Project
If you have a sloped yard, a failing wall, or just want to understand what’s possible with your outdoor space, call or text 613-795-2017 or use the contact form. We work throughout Ottawa and surrounding communities, including Kanata, Barrhaven, Nepean, Stittsville, Manotick, Richmond, Carleton Place, and Almonte.
Frequently Asked Questions
How tall can a retaining wall be without a permit in Ottawa?
The City of Ottawa generally requires a permit for retaining walls over one metre in height, particularly when they’re near property lines or affect drainage patterns. For walls over certain heights or with surcharge loading (a driveway or structure above the wall), engineering drawings may be required. We flag these situations during the quote visit and can help you understand what applies to your property.
My existing retaining wall is leaning. Can it be repaired or does it need to come down?
It depends how far it’s moved and what’s behind it. A wall that’s leaning slightly and caught early can sometimes be dismantled, the drainage issue corrected, and rebuilt. A wall that’s moved significantly or has structural damage usually needs to come down and start fresh. We assess case by case — there’s no single answer without seeing it.
What's the difference between armourstone and interlock retaining wall systems in terms of cost?
Armourstone is typically less expensive for large, high walls because the installation is faster. Interlocking systems take more labour per square foot but offer more design flexibility at lower heights. For most residential retaining walls under three feet, an interlocking system is a very practical choice. For anything taller or with significant soil load behind it, armourstone is usually the better call.
How long does a retaining wall installation take?
A single residential retaining wall — say, 30 to 50 feet long at moderate height — typically takes two to four days, depending on site access, material type, and whether we’re doing drainage work at the same time. Larger projects or walls combined with patios and grading take longer. We give you a timeline in the quote and stick to it.
