Boulder and Rock Retaining Walls in Christchurch
Top Retaining Walls Christchurch builds boulder and rock retaining walls, where large angular rock is placed by machine, keyed into a prepared trench and battered back into the bank. Each rock is set to bear on the ones below rather than simply stacked on them.
- Machine placed boulders, keyed and battered back
- Free draining, nothing to rot or corrode
- Suits rural and lifestyle settings
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Done well they are one of the best looking retaining options and they last effectively forever, because there is nothing in them to rot or corrode. Done badly they are a pile of rock that moves in the first big rain. MBIE's Canterbury review is blunt about it: many non engineered rock facings collapsed in the 2010 and 2011 earthquakes, exposing near vertical faces of undisturbed loess behind them.
Building a rock retaining wall that stays put
Foundation and key
The base course sits in a trench below finished ground so the wall cannot slide forward. On a slope that trench is benched level rather than following the fall.
Batter
The face leans back into the bank. That batter is what puts the weight of the rock over the material it is holding. A vertical rock wall is a rock wall waiting to fall over.
Bearing, not stacking
Each rock is turned and set so it beds on at least two below it. Placing rock quickly is easy. Placing it so it locks is the skill, and it is most of the labour cost.
Where boulder retaining walls suit a Canterbury property
Rural and lifestyle boundaries, large banks, stream edges and anywhere the aesthetic is meant to be natural. They read correctly on a Prebbleton or West Melton block in a way a block wall does not.
They take a lot of space at the base because of the batter, which rules them out on tight urban boundaries. And they are not the answer under a surcharge unless specifically engineered, which is exactly the mistake the earthquake evidence exposed.
Rock retaining wall cost and sourcing local stone
About $190 to $470 per lineal metre. The variables are rock supply, cartage and machine time, and rock is heavy so cartage distance matters more than for most materials.
Local Canterbury rock reads better than imported stone and usually costs less delivered. We show you the source before it arrives, because colour and fracture pattern make a very visible difference.
Boulder and Rock Walls at a glance
- Method
- Machine placed, keyed into a trench, battered back into the bank
- Cost
- About $190 to $470 per lineal metre
- Drainage
- Free draining through the face, geotextile behind
- Space
- Needs real depth at the base because of the batter
- Not suitable for
- Surcharge loads unless specifically engineered
- Earthquake lesson
- Non engineered rock facings performed badly in 2010 and 2011
Boulder and Rock Walls in Christchurch: common questions
Do rock walls need drainage?
The wall drains itself, but geotextile behind it is still needed so soil cannot wash through the gaps.
How long do they last?
Effectively indefinitely with a proper key and batter. There is nothing in them to rot or corrode.
Can a rock wall hold a driveway?
Not without specific engineering. Surcharge on an unengineered rock wall is exactly the failure mode that showed up across Christchurch after the earthquakes.
Where does the rock come from?
Local Canterbury quarries. We show you the source first, because colour and fracture make a big visual difference.
How big do the boulders need to be?
Big enough that their own weight resists the ground behind, which scales with the retained height. On a low garden wall that can be rock a person could move. On anything structural it is machine placed rock measured in tonnes, and the base course is usually the largest material in the wall.
Can you plant a rock retaining wall?
Yes, and it suits them. Pockets of soil between the rocks take low growing natives and succulents well, and planting softens the face considerably within a couple of seasons. It also helps bind the surface soil behind the wall.
Why did my rock wall collapse in the earthquakes?
Almost certainly because it was a facing rather than an engineered retaining structure. MBIE's Canterbury review records that many non engineered rock facings collapsed in 2010 and 2011, exposing near vertical faces of undisturbed loess behind them. Rebuilt properly, the wall is keyed into a trench and battered back rather than stacked against the face.
Recent Christchurch jobs
Boundary wall between us and the neighbour on a new build. Sorted the levels, the consent question and the fence on top in one job. Turned up when they said and left the site clean every night.
Builder here. I use them on subdivision work because the paperwork comes back complete. PS1 up front, PS4 at the end, no chasing.
Wall failed after the big rain and took part of the bank with it. Made safe within two days and rebuilt a month later with real drainage behind it.
Terraced the back lawn into two levels. Fast, tidy, fair price, and the drainage was done properly.
Get a price for boulder and rock walls in Christchurch
Free site visit, a fixed written quote, and a straight answer on what the wall actually needs.
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Four questions and you are done.