Top Retaining Walls Christchurch builds timber pole and rail retaining walls right across Christchurch. This is the wall most Canterbury sections end up with. It goes up quickly, it costs less per metre than any other type, and it holds a 1m to 1.4m change in level without complaint.
We dig the post holes about 450mm across and take the depth down to roughly the same measurement as the finished wall height. A 1.2m wall gets a 1.2m hole. Poles go in at 1.2m centres, we brace them plumb, then fill each hole with ordinary grade concrete and leave it to cure.
Rails go on the soil side of the poles, so the soil pushes the rail into the post instead of pulling it off the fixings. We use 150 x 50 or 200 x 50 H4 rough sawn boards and hot dipped galvanised nails, because galvanised fixings are the ones that survive wet timber.
| Poles | 200mm small end diameter, H5 treated, 1.2m centres |
|---|---|
| Rails | 150 x 50 or 200 x 50 H4 rough sawn, fixed on the soil side |
| Footing | About 450mm across, depth roughly equal to wall height, ordinary grade concrete |
| Drainage | 300mm free draining metal, 110mm perforated coil, geotextile wrap |
| Fixings | Hot dipped galvanised nails or coach screws |
| Practical height | Up to 1.5m with no surcharge above, then it needs engineering |
| Build time | Two to four days for a typical 10m to 15m wall |
| Expected life | 25 to 40 years while the drainage stays clear |
H5 is the treatment level for timber that sits in the ground in wet conditions. H4 is not enough for a buried post, even though it looks identical on the rack. The poles have to be H5 and the rails above ground can be H4.
A properly drained H5 pole wall commonly lasts 25 to 40 years. The same wall with no drainage behind it can rot out in 10 to 15, because the post never gets a chance to dry.
We lay 150mm of clean drainage metal along the base, sit the perforated drain coil on top of it, then cover the coil with another 250mm of metal. Geotextile cloth wraps the top and back of that zone so silt cannot wash in and block it. The coil discharges to daylight, or into stormwater where the site allows.
Almost every failed wall we get called to look at in Christchurch failed the same way. Water sat behind it, the soil got heavy, and the posts slowly leaned out.
Pole walls get structurally marginal past about 1.5m, and they are a poor choice when a driveway, shed or parked vehicle sits above. In those cases we quote a block or engineered wall instead and tell you why.
On a Port Hills section with loess soil we often step the job into two shorter walls instead. Two 1.1m walls with a planted terrace between them usually cost less than one engineered 2.2m wall, and they keep you out of the consent process.
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.
As a working rule the hole goes about as deep as the wall is tall. A 1.2m high wall gets a 1.2m deep hole, filled with concrete. Softer ground or a surcharge above the wall pushes that deeper, and that is a call we make on site.
Usually yes, but the soil being retained belongs to someone, and whoever benefits from the wall normally pays for it. Sort that out in writing with your neighbour before we start. We can supply the quote and drawings you need for that conversation.
Not if the wall retains 1.5m of ground or less and carries no surcharge above it. Add a driveway, a building or sloping fill above the wall and you need a building consent from Christchurch City Council whatever the height.
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.
Call [PHONE] or answer three quick questions. The site visit and the written quote cost you nothing.
