Retaining walls
Retaining walls that hold their line
Retaining and garden walls in block and natural stone, drained behind every course and founded below the ground that heaves.
Retaining wall installation starts behind the face
Good retaining wall installation is mostly invisible. The face you select and photograph does far less work than the clean stone packed behind it. When a wall leans, the cause is nearly always back there.
Wet soil is heavy, and it presses hard on anything in front of it. Frost adds more pressure on top of that. A lasting wall therefore depends on one discipline: keeping the retained ground from ever staying saturated.
How a wall is built properly
- Base course below grade. Set level on compacted granular, below finished grade. Any error here repeats up every course.
- Drainage stone to full height. Clean angular aggregate behind the units, never the excavated soil returned.
- Filter fabric. Placed between native soil and stone so fines cannot clog the voids.
- Perforated drain at the base. Run to a daylight outlet, so collected water leaves instead of pooling.
- Compacted lifts. Backfill placed and compacted as each course goes up, never dumped at the end.
- Batter and geogrid as required. Setback into the slope, with reinforcement tied back where height and surcharge call for it.
Reading a slope
What a difficult grade can give back
Most owners treat a slope as something to live with. Usually it is floor area that has not been levelled yet.
Level ground from a bank
A single wall in the right spot creates a terrace wide enough for a table and chairs.
Two short walls, not one tall
Splitting the height keeps each wall smaller, softer to look at, and clear of heavier design requirements. The step between becomes a planting bed.
Seating in the structure
Set at seat height with a deep cap, a wall around a patio replaces loose chairs.
Beds that stay put
Terraced planting keeps topsoil in place through spring runoff instead of losing it downhill.
One wall, several jobs
At a boundary with a grade change, the same wall can hold soil, carry a fence and mark the edge.
Water directed on purpose
Building the wall is the time to decide where runoff goes, and to send it away from the foundation.
Where it goes
Front courts, terraces and property lines
Residential retaining work is rarely a towering engineered structure. More often it lets a front court meet the door at one level. Sometimes it stops a neighbour's higher grade from spilling onto a driveway. Elsewhere it divides a rear slope into two flat garden rooms.
Each of those follows identical rules, since short walls retain wet clay too. Height does not decide whether a wall survives. Drainage behind it does.
Low walls around patios and beds have their own guide: garden and seat walls →
Go deeper
Retaining wall guides
Questions
Retaining walls, answered
What actually makes a retaining wall fail?
Water held behind it. Saturated soil weighs far more than drained soil and pushes harder on the wall face, and freezing raises that pressure again. A wall with no clean stone, no filter fabric and no outlet at the base carries a load it was never sized for. The usual sequence is a bulge, then a lean, then a collapse.
How high can a wall be before it needs an engineer?
That threshold is set by the municipality, so check the by-law that covers your lot before design starts. It tends to be lower than owners expect. A driveway, a slope or a building near the top of the wall adds load and can bring the requirement into play sooner. Where a wall is close to that line, it should be built to an engineered design and permitted accordingly.
Segmental block or natural stone?
Choose segmental block where the wall carries real structural load, and natural stone where appearance leads. Block units are uniform, set back automatically and lock course to course, which suits taller or loaded walls. Coursed stone and armour stone give a depth and irregularity no manufactured unit matches, and they suit low walls and garden work. Many properties use both: block where the load is, stone where people look.
Do I need a railing or fence along the top of a wall?
Often, once the drop beside a walkway or patio passes a height the local by-law sets. Confirm the requirement with the municipality during design. Settling it early matters, because a guard needs anchorage planned into the cap or footing. Retrofitting one into a finished wall is awkward and rarely as clean.
Can a wall be built on or near the property line?
It can, but location affects both the structure and the legal picture. The wall bears on soil on both sides, and its drainage and backfill extend behind the face. Where the grade change sits at the boundary, agree the approach with the neighbour first and check municipal requirements before design begins.