About Top Retaining Walls Christchurch

We do the earthworks, the drainage, the wall and the backfill as one job. That is deliberate, because the most common way a retaining wall goes wrong is that three trades each did their part and nobody owned the bit in between.

Two things decide whether a wall lasts thirty years or leans in five, and neither of them is the timber or the block. The first is drainage. Water building up behind a wall is what actually pushes it over, and saturated backfill can roughly double the load a wall was designed for. Slotted pipe on a fall, free draining metal, geotextile so silt cannot choke it, and an outlet that goes somewhere real are part of every quote we write rather than a line that gets cut when the price looks high.

The second is whether anyone worked out what the wall is actually holding before they priced it. On a Port Hills section that means treating loess as what it is. Undisturbed and dry it stands at a near vertical face with high apparent cohesion, which is exactly what convinces people the ground is stable and the wall can be modest. Wet, that strength is gone, and residential design here commonly assumes zero cohesion and a thirty degree friction angle.

How we quote

A free site visit first, with levels taken, so everyone is talking about the same wall. Then a fixed written price that separates construction from the third party costs. Engineering, geotechnical investigation and council fees are quoted at cost and shown as their own lines, because they are not our money and we would rather you see exactly what they are.

Where a repair and a rebuild are both real options, both go on the same quote with the difference in front of you. Plenty of leaning walls have sound posts and a blocked drain, and on those a repair at roughly $105 to $365 per lineal metre holds where a rebuild would be several times that. Where the posts have rotted along the whole run we say so, because patching that buys a season and costs the money twice.

Consent, and why we raise it first

Under Schedule 1 of the Building Act a retaining wall is exempt if it retains no more than 1.5 metres of ground and supports no surcharge. Both conditions, not either, and the surcharge test catches far more Christchurch walls than the height rule does. A driveway, a parked car, a deck, a building footing or ground that keeps rising behind the wall all count.

We work that out at the site visit rather than after you have committed to a budget, because building without a consent you needed is an offence under section 40 carrying a maximum fine of $200,000, and it surfaces the moment you try to sell. Where a wall is consented work we bring in the engineer, get the PS1, lodge the application, manage the inspections and hand over the PS4.

What the Canterbury earthquakes taught us

MBIE's guidance on the seismic design of retaining structures for Canterbury is unusually specific about what happened. Engineered concrete block walls generally performed well, and walls that were propped or buttressed damaged less than pure cantilevers. Retained fill settled significantly behind flexible timber pole walls. Many non engineered rock facings collapsed outright. And several failures were initiated by slope instability above or below the wall rather than by the wall itself.

That last point changes how we assess a failing wall. Where there are fresh tension cracks in the ground above or bulging at the toe below, the slope is moving and the wall is a passenger. We say so and recommend a geotechnical engineer rather than quoting a structure that will move again.

Where we work

All of Christchurch city, the Port Hills from Cashmere round through Huntsbury, Mount Pleasant and Sumner to Lyttelton, and across the flat through Riccarton, Fendalton, Halswell, Wigram and Papanui. Out through Selwyn to Rolleston, Lincoln and Prebbleton, and north through Waimakariri to Kaiapoi and Rangiora, all with no travel loading on the quote.

Our main services

• Retaining Wall Builders in Christchurch, free site visit and a fixed written quote.
• Retaining Wall Repair in Christchurch, we find out why it moved before quoting anything.
• Timber Retaining Walls in Christchurch, h5 treated posts set in concrete, H4 sleepers.
• Concrete Block Walls in Christchurch, reinforced and grout filled on a designed footing.
• Poured Concrete Walls in Christchurch, monolithic cantilever walls on an engineered footing.
• Gabion Retaining Walls in Christchurch, drain freely, so no water builds up behind them.
• Retaining Wall Replacement in Christchurch, old wall removed and disposed of.
• Engineered Retaining Walls in Christchurch, for walls over 1.5m or carrying any surcharge.
• Retaining Wall Drainage in Christchurch, the single most common cause of wall failure.
• Consent and Design in Christchurch, a straight answer on whether you need consent.

Everything else we are called out for

The list below is the full index. If what you need is not on it, it is still worth asking, because most of these pages started as a job somebody rang about.

• Concrete Sleeper Walls
• Steel Post and Sleeper
• Crib Retaining Walls
• Segmental Block Walls
• Geogrid Reinforced Walls
• Boulder and Rock Walls
• Natural Stone Walls
• Stone Faced Walls
• Macrocarpa Walls
• Pole and Rail Walls
• Cantilever Walls
• Anchored Walls
• Sheet Pile Walls
• Mass Block Walls
• Precast Panel Walls
• Driveway Retaining Walls
• Garden Retaining Walls
• Terraced Retaining Walls
• Pool Retaining Walls
• House Platform Retaining
• Boundary Retaining Walls
• Commercial Retaining Walls
• Lifestyle Block Walls
• Leaning Wall Repair
• Rotten Timber Repair
• Drainage Repair
• Earthquake Wall Repair
• Wall Stabilisation
• Retaining Wall Insurance Claims
• Excavation
• Backfill and Compaction
• Geotechnical Reports
• Producer Statements
• Handrails and Fences