Most retaining walls going into yards around Coquitlam and the rest of the Lower Mainland are block walls. If you have been quoted for one and want to know what you are actually buying, this is the short version.
What a block wall is
A block retaining wall, sometimes called a segmental wall, is built from manufactured concrete units stacked without mortar. Allan Block is one brand of these units. There are several others and they work on the same principle.
The blocks lock together with a lip or a pin at the back of each course, so every row sits slightly behind the one below it. That backward step is called setback or batter, and it is doing real work: it leans the wall into the slope so the weight of the soil helps hold the wall rather than only pushing on it.
For a low wall, that mass and setback is enough on its own. For a taller one, the wall gets tied back into the hillside with geogrid, which is a structural mesh laid between courses and running back into the compacted fill. At that point the wall and the soil behind it are acting as one block of weight instead of a facing holding back a slope.
Why block is the common choice here
It handles ground movement. Dry-stacked block flexes slightly. Coastal clay swells when it is wet and shrinks when it dries, and a wall with no mortar joints tolerates that better than one rigid pour.
It drains. The open joints between blocks let water escape through the face rather than build up behind it. That is a real advantage in a climate that rains for five months.
It can be repaired in sections. If part of a block wall settles, that section can often be taken apart and reset. A cracked concrete wall is usually a full replacement.
It curves. Block follows a curve or steps down a slope without formwork, which matters when the wall is also a garden edge or a seating height.
How it compares
Poured concrete. Stronger per square foot and the right answer where a wall is structural or space is tight. It costs more, needs forms and cure time, and when it cracks it stays cracked. Rigid walls also need drainage designed in deliberately, because nothing escapes through the face.
Natural rock or boulder walls. Good where the look suits the property and there is room, since a rock wall needs more depth front to back. Placement is machine work and the result depends heavily on who is running the machine. Not usually cheaper than block once the rock is delivered.
Timber. The shortest life of the three, and the cheapest to put in. Pressure-treated ties suit a low wall, a garden terrace or a planter, and they look right against an older house or an existing timber yard. The limit is what wet ground does to buried wood: rot starts on the back face where nobody can see it, and the tiebacks holding the wall into the slope usually go before the front of it moves. On a tall wall, or a slope that stays wet through the winter, that trade is not worth making. On a low one it often is. We build timber tie walls alongside block and rock, so the answer you get is about your yard rather than what we happen to stock.
The part that decides whether it lasts
The block is not what fails. We wrote about that in more detail in why retaining walls lean, bulge and fail, and it holds true whatever the wall is made of.
What matters is underneath and behind:
The base. A compacted gravel base, dug below the frost and topsoil layer, level across its length. The first course sets the geometry for every course above it. If the base settles unevenly, the wall goes out of level and the courses separate.
The drainage. Clear crush behind the blocks, filter fabric to stop soil migrating into it, and a perforated pipe at the bottom that actually runs somewhere. Water is the load that pushes walls over, so the job is giving it a way out.
The backfill. Free-draining material behind the wall, not the clay that came out of the hole.
A wall built with those three done properly will outlast the people who bought it. Skip any one of them and it will move within a few winters, no matter which block was used.
Heights and engineering
In BC, retaining walls over roughly 1.2 metres generally require engineering, and many municipalities require a permit at that height. Taller walls usually need geogrid. Tiering two shorter walls instead of building one tall one is sometimes an option, though the spacing between tiers matters structurally and is not a way to dodge the engineering.
Worth checking with your municipality early, because it affects both the design and the budget.
Which one is right for your yard
It usually comes down to how tall the wall needs to be, what is above and below it, how the water moves across the site, and what you want it to look like. On most residential slopes here, a block wall with proper drainage is the sensible answer.
We build retaining walls across the Lower Mainland and the Fraser Valley, in block and in natural rock, and we dig the drainage side of the job ourselves. You can see walls we have built, including a before and after of a slope rebuilt from bare dirt.
Send a photo of the slope and rough measurements and we will come look. The quote is free.