A slope can be held back one of two ways: one tall wall, or a series of shorter walls stepping up the hill with flat terraces between them. Where the site allows it, terracing usually wins — it looks better, every terrace becomes plantable or usable ground, and shorter walls often stay under your city's permit and engineering thresholds that one tall wall would blow past.
But terraces are not a loophole. They only behave as independent, simple walls when the geometry is respected — and the geometry comes down to one rule.
If the lower wall is 3 ft tall, the next tier starts at least 6 ft back from its face. Hold that setback and each wall carries only its own ground — the manufacturers' published design guidance (this is Allan Block's standard for segmental walls, and the industry norm) treats the tiers as independent walls, each designed like any other garden-height wall. Hold the setback and you can step a slope in as many tiers as it takes.
Move the tiers closer than that, and something invisible happens: the upper wall's weight and retained soil start pressing on the ground the lower wall is holding. The lower wall is now carrying a load it was never designed for. At that point the walls stop being two simple walls — the whole slope has to be designed as one engineered system, with the combined height treated the way a single tall wall would be.
The failure mode is exactly what you'd expect, on a delay: the lower wall bulges and leans from pressure you can't see, sometimes years later. Fixing it means rebuilding the bottom wall while the top one sits over your head — the most expensive possible order of operations.
Second rule, simpler: each wall going up the slope is the same height or shorter than the one below it. The heaviest lifting happens at the bottom of the hill, so the strongest, tallest wall belongs there. A short wall at the bottom with a tall wall looming above it is a system designed backwards.
The flat ground between your walls reads as garden space, but structurally it's something else: it's the foundation of the wall above it. On our builds that ground gets filled and machine-compacted in thin lifts — the same compaction discipline as the zone behind any single wall — before the upper wall's base trench is even cut.
Skip that and the upper wall is sitting on loose fill. It settles, tips forward, and takes the terrace planting with it. If you read our Allan Block wall guide, you'll recognize the theme: the parts of a wall that fail are almost never the parts you can see.
Free site visit — we look at the grade, the soil, and your city's rules, and tell you straight whether tiers, one wall, or an engineered system is the right answer. Ballpark estimate based on what we see.
Each wall in a terrace gets the full drainage package — its own perforated drain pipe at the base, sloped to daylight, with clean drainage gravel behind the blocks — not just the bottom one. Water that gets into an upper terrace has to have somewhere to go that isn't "behind the lower wall."
Skip the upper drains and the bottom wall becomes the collection point for the entire slope's water. In Lower Mainland clay — which holds water like a bowl — that makes it the highest-pressure spot on the property, and the first place to bulge. Walls here fail from trapped water far more often than from soil.
Most Lower Mainland municipalities set a wall height — commonly around 1.2 m (4 ft), lower in some cities — above which a retaining wall needs a permit and usually an engineer. Terracing legitimately keeps each individual wall under that trigger, but cities know the trick: most bylaws treat closely-spaced tiers as one combined wall. Some go further — Pitt Meadows, for example, applies its engineering requirement when the overall slope across stepped walls is steeper than 2H:1V, a rule many homeowners have never heard of.
The spacing rule and the bylaws point the same direction: generous setbacks make walls independent in the eyes of both physics and the permit desk. Check your city's exact thresholds with our free permit checker — it covers 22 Lower Mainland and Fraser Valley municipalities, including how each one treats terraced walls.
Some slopes can't fit the setback — the yard isn't deep enough, or the grade is too steep for gravity walls at any spacing. Some terraces carry loads: a driveway, a parking pad, a hot tub, a structure. In those cases the system gets designed as one engineered wall — geogrid reinforcement, global stability analysis, and an engineer's stamped drawings — and that's not red tape, that's the correct product for the site.
Our rule on this is simple: we'll tell you which side of the line your slope is on before we put a number on anything, and when an engineer is needed we coordinate the drawings and the permit as part of the project.
Done right, a terraced slope stops being a liability and becomes the best-looking part of the property: planted benches of hydrangeas and grasses instead of a bare bank, steps integrated into the tiers, and flat ground where there was none. The same block families build raised beds and garden walls, so the terraces, stairs, and planters all read as one build.
Tell us about your project and we'll get back to you with a free, no-obligation estimate. We service the entire Lower Mainland.
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