Top Retaining Walls Christchurch builds concrete block retaining walls across Christchurch. A reinforced masonry wall sits on a concrete footing with steel running up through the cores, and once the cores are grout filled the whole thing works as one structure. It is the wall you build when something above it matters.
We excavate down to firm bearing and pour a reinforced concrete footing with starter bars standing up out of it. The blocks thread down over those bars course by course, we tie in horizontal steel as the wall rises, then fill the cores with grout so the steel, block and footing act together.
The drainage layer goes in behind before any backfill, because once the wall is up you cannot get back there. Clean metal, drain coil at the base, geotextile over the top.
| Footing | Reinforced concrete, excavated to firm bearing |
|---|---|
| Blocks | Standard masonry units, grout filled cores |
| Steel | Vertical starters from the footing, horizontal bars as it rises |
| Drainage | Free draining metal, drain coil, geotextile, weep holes where used |
| Height | Engineered design and consent above 1.5m or with any surcharge |
| Finish | Bare, plastered and painted, or sealed |
| Best for | Driveways, buildings or pools above the wall |
MBIE reviewed how retaining walls behaved after the 2010 and 2011 earthquakes. Engineered concrete block walls generally came through well, and walls that were propped or buttressed showed less damage than pure cantilever walls. Block basement walls built into the house did particularly well.
That is a real reason people in Christchurch pay more for block. The performance data is local and it is recent.
Any wall retaining more than 1.5m of ground needs a building consent and a chartered engineer's design. So does a shorter wall with a surcharge, which means a driveway, a building, a pool or sloping fill above it.
Reinforced block is the type we most often build to an engineer's drawings, because it takes reinforcing easily and the inspector can see the steel before the grout goes in.
Bare grey block is honest and cheap. Plaster and paint gives you a clean modern face, and it hides the joints. Either way we recommend sealing masonry, because persistent moisture brings efflorescence and staining out through the face.
We cap the top course, which stops water getting straight down into the cores and keeps the top line looking deliberate.
Every wall we build gets drainage. At least 300mm of clean free draining metal, a perforated coil at the base running to a real outlet, and geotextile over the top so silt cannot block it. It is not an optional line on our quotes.
For the same height, yes, and by a wide margin once it is reinforced and grout filled. It also carries surcharge load that timber cannot, which is why driveway walls are usually block or poured concrete.
Some designs use them and some rely on the drain coil at the base. Either way the point is the same, which is giving water a way out so it never pushes on the back of the wall.
Yes, and it is often the right call there. Loess soil and slope mean most Port Hills walls need engineering anyway, and block takes an engineered design well.
Our old wall was rotten right through and leaning into the neighbour's place. They pulled the lot out, put proper drainage behind the new one and had it finished in three days. Swept the site clean every afternoon before they left too. Tidiest crew we have ever had here by a long way.
They sorted the consent, which was the bit I was dreading. Dealt with the council so I never had to, and kept me in the loop the whole way through. The driveway sits right above it and has not shifted a millimetre.
Steep section, shocking access, and they still made it look easy. They suggested two smaller walls instead of one big one, which saved us thousands in engineering fees. The terrace in between is now my favourite part of the whole garden.
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