Retaining walls and steps

A retaining wall is a structure pretending to be landscaping, holding back many tonnes of wet soil that on Barrhaven clay gets heavier every spring. Walls built as decoration fail by leaning outward at the top, and by then the repair is a rebuild.

Step one: establish whether this is regulated work. In Ontario a retaining wall over 1,000 mm in exposed height is treated as a designated structure and generally requires a building permit and a design from a licensed professional engineer confirming compliance with Part 4 of the Building Code, as municipal building departments set out (City of Barrie building services information sheet). Confirm the threshold and the process with City of Ottawa building services for your specific wall, because siting near a property line, a road or a building can change the answer. You can verify an engineer's licence in the PEO directory.

Step two: locates and layout. A locate request to Ontario One Call is legally required, free, and goes in at least five business days before digging (Ontario One Call). The excavation behind the wall line is always wider than homeowners expect, because the reinforced zone behind the blocks has to be built too.

Step three: the base trench. This is where a wall is won. The trench is excavated deep enough that the first course of block sits buried, a common rule of thumb being about one tenth of the wall height plus the block depth. Compacted granular base goes in, levelled precisely, because every error in the first course multiplies up the wall.

Step four: courses, backfill and drainage. Blocks are laid course by course with the specified setback. Behind them goes clear stone and a perforated drain pipe at the base that daylights somewhere sensible. That drain is not optional: water building up behind a wall creates hydrostatic pressure, and on clay that pressure is the usual cause of failure.

Step five: geogrid, where the design calls for it. Geogrid is layered horizontally back into the retained soil, tying wall and soil mass together so they act as one. Taller walls, and walls with a driveway, slope or structure above them, need it. Spacing and length come from the engineer's design rather than from experience.

Step six: capping and finishing. Cap units are adhered, the top is drained so surface water does not run over the face, and the area above is graded away from the backfill.

How long it takes. A low garden wall of ten or fifteen metres is typically two to four days. A taller engineered wall with geogrid runs one to three weeks. Add the locate week, plus permit and engineering lead time, which can be several weeks on its own.

Steps, which fail for the same reasons. Interlock and block steps sit on the same principles as a wall, and they go wrong in the same way. A set of steps built on backfill that was never compacted, or on a base that stops short of frost-resistant depth, will rock, separate and tilt away from the house within a few winters. Rebuilding means excavating to a proper compacted base, building up with solid units bedded and adhered rather than dry-stacked, draining behind and beneath them so water is not trapped, and tying the top landing to the house without relying on the house to hold the steps up. Loose steps at a front door are also a trip hazard on a February morning, which is a reason to treat them as a repair rather than a cosmetic job.

What it costs in Ottawa in 2026. Indicative ranges only, and note that this site's price guide does not yet carry a wall or step row, so treat these as planning figures rather than quotes. Segmental block walls are usually priced by the square foot of exposed face, commonly around $40 to $90 per square foot installed, with armour stone and natural stone higher. A set of rebuilt interlock or block steps is often $1,500 to $5,000 depending on the number of risers, the landing and whether a railing is involved. Engineering fees for a designed wall are separate, commonly several hundred to a few thousand dollars. What moves the price: height, length, block choice, excavation, geogrid and machine access.

What makes a Barrhaven wall different. Champlain Sea clay is why drainage dominates the design here. It drains slowly and loses much of its strength when disturbed (NRC), so soil behind a wall stays saturated far longer than it would on sand. Frost is the second force: the Building Code requires foundations as deep as 1.2 m in clay (OBC 9.12.2.2), and a wall with poor drainage gets lifted and pushed by ice each winter. Barrhaven's newer subdivisions, Half Moon Bay and Stonebridge among them, were graded with engineered slopes and swales, and a wall that interrupts a swale can cause a water problem for a neighbour, which is a legal issue as well as a practical one.

Who should do the work. For anything over about a metre, a licensed professional engineer designs it and the City permits it. The wall builder itself is unlicensed work, so check insurance, WSIB coverage and examples of walls they built years ago rather than last month. Look along the top course of an older wall: a straight line means the drainage worked.

What to ask before you hire. How tall is the exposed face, and does that need a permit and an engineer. What is going behind the wall, how much clear stone and is there a drain pipe. Where does that drain discharge. Is geogrid in the design, at what spacing. How deep is the base trench and is the first course buried. What are you backfilling with. Who is handling the permit. What is the warranty on movement, and what does it exclude.