Steel Post and Sleeper Retaining Walls in Christchurch
Top Retaining Walls Christchurch builds steel post and sleeper retaining walls. Galvanised H section posts are set in concrete and either timber or precast concrete sleepers slot down between the flanges. It is the same principle as a timber wall with the weakest component replaced.
- Galvanised steel H posts, timber or concrete infill
- Longer spans and fewer holes than timber posts
- The post outlives the infill, which can be swapped
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On a timber wall the post does all the structural work and it is also the part sitting in wet ground. Swapping to a galvanised steel section removes that conflict. The post carries far more bending for its size, which means wider spacing and fewer holes, and it does not rot.
What steel posts change about a sleeper retaining wall
Longer spans, fewer posts
A steel section carries more bending than a timber post of similar footprint, so posts sit further apart. On a long boundary that is noticeably fewer holes and less concrete.
Taller walls without going to block
Steel post walls comfortably handle heights where timber posts would need to be impractically large. Past 1.5 metres of retained ground they still need engineering and consent like anything else.
Replaceable infill
If timber sleepers eventually weather out they lift from the channels and new ones drop in. The structural part of the wall stays where it is.
Galvanising and ground contact on coastal Christchurch retaining walls
Everything depends on the coating. Hot dip galvanising to an appropriate thickness gives the post its life, and the critical zone is at and just below ground line where the steel is alternately wet and dry.
Near the sea at Sumner, or on damp ground in Heathcote Valley, we specify heavier coating and encase the buried section in concrete rather than backfilling with spoil. Cutting a galvanised post exposes bare steel at the cut, so cuts get treated on site.
Steel post retaining wall cost and when to choose it
About $210 to $525 per lineal metre depending on infill, with timber sleepers near the bottom of that and precast concrete panels near the top.
It is the right call on long boundaries, on walls approaching 1.5 metres, and anywhere post rot has already been the failure mode once. On a low garden wall it is more system than the job needs.
Steel Post and Sleeper at a glance
- Posts
- Hot dip galvanised steel H section, concreted in
- Infill
- H4 timber sleepers or precast concrete panels
- Cost
- About $210 to $525 per lineal metre
- Advantage
- Longer spans, no post rot, replaceable infill
- Coastal
- Heavier galvanising near the sea, site cuts treated
- Consent
- Same 1.5m and surcharge rules as any wall
Steel Post and Sleeper in Christchurch: common questions
Do steel posts rust?
Hot dip galvanised posts have a long life. The vulnerable point is ground line, which is why we encase the buried section in concrete and treat any site cuts.
Can I use timber sleepers with steel posts?
Yes, and many people do. You get the timber look with a post that will not rot.
How far apart can the posts go?
Further than timber, but it is set by the sleeper span rating and the retained height rather than by preference.
Is it worth it on a low wall?
Usually not. On a low garden wall timber posts do the job for less.
Can steel posts be used to repair an existing timber wall?
Sometimes, where the sleepers are sound and only the posts have failed. New galvanised posts go in between or beside the old positions and the existing sleepers drop into the channels. It works best where the wall is straight and the sleeper sizes are standard, and it is considerably cheaper than a full rebuild.
Do steel posts need painting?
Not if they are properly hot dip galvanised. Painting is cosmetic rather than protective, and if you do want them dark, it needs an etch primer suited to galvanising or it will peel. What does matter is treating any cut ends on site, because a cut exposes bare steel.
How do steel post walls handle a fence on top?
Better than almost anything else, because the post continues up and the fence fixes straight to it. There is no separate fence post to set, no drilling into a finished wall, and the wind load from the fence goes into a member designed to take bending.
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.
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