Retaining Walls in Dunedin and Mosgiel

Nearly every retaining wall that fails, fails at the drainage

A retaining wall is not really holding back soil. It is holding back soil plus whatever water is in it, and wet soil is enormously heavier and pushes far harder than dry soil. Which is why the walls that bulge, lean and eventually come out are almost never the ones with too few posts - they are the ones with nowhere for the water to go.

So the parts of our retaining walls you cannot see are the parts that matter: drainage metal behind the wall, a drainage coil at the base taking water somewhere sensible, and geotextile keeping the soil out of the drainage. It costs more on the quote than a wall without them, and it is the difference between a wall that lasts and a wall you pay for twice.

This is Dunedin, so it matters more here. City sections are steep, the rain is real, and a lot of the older walls around the place were built as timber-and-hope.

What we build

Timber retaining walls

Treated timber posts with sleeper or plank facing is the most common retaining wall on a Dunedin section, and for good reason - it suits the ground, it can follow a curve or a contour, it goes in without heavy plant on a tight site, and it can be built to match the fence going on top of it. Post size, spacing and embedment depth all get set by the height of the wall and what is behind it.

Terracing and garden walls

A steep back section is a lot more useful as two or three flat terraces than as one slope you cannot mow. Low garden walls, terraced beds and stepped walls turn dead ground into lawn, vegetable garden or somewhere to put a table. Often the cheapest way to make a Dunedin section feel bigger.

Repairs to existing walls

If a wall has started to lean, bulge, or push a fence out of line above it, get it looked at before it moves further. Sometimes the fix is retrofitting drainage and replacing the failed section. Sometimes the wall is done and honesty is cheaper than optimism. We will tell you which, and if it is beyond us or needs an engineer's design we will say so rather than have a go.

Retaining and fencing, at the same time

On a sloping section the fence and the retaining wall are one job. The wall sets the level, the fence goes on top, and the two have to be designed together - posts sized and positioned for both loads, and the fence height measured from the right side of the wall. Getting one contractor to do both means nobody is waiting on anybody, and there is no argument later about whose post moved.

We do the fencing and the deck as well, so a job that involves levelling a bank, retaining it, fencing the boundary and putting a deck off the back of the house is one quote and one crew.

Consents and engineering

Retaining walls are one of the areas where the rules genuinely bite. Height, what the wall is supporting, whether there is a building or a driveway above it, and how close it is to a boundary all affect whether you need a building consent and whether it needs a specific engineering design. We will tell you at quote time what we think your wall needs, and the Dunedin City Council or your local council will confirm it. We will not build you a wall that cannot be signed off, and if your job needs an engineer we will say so up front.