A retaining wall that is pulling away from the soil — sometimes called wall lean or wall displacement — is a serious structural warning sign that should not be ignored. Depending on the wall's height, age, and construction type, the fix could range from improving drainage to a full rebuild. Here's how to assess the problem and decide on the best course of action.
Why Is Your Retaining Wall Pulling Away?
Understanding the cause is the first step to a lasting repair. The most common reasons include:
- Poor or blocked drainage – Water builds up behind the wall, creating hydrostatic pressure that pushes the wall outward.
- Inadequate or missing deadmen/tie-backs – Timber or concrete walls rely on anchors extending back into the soil. If these have rotted or were never installed, the wall loses its grip.
- Overloading – Heavy vehicles, new structures, or soil added above the wall can exceed its original design load.
- Soil movement or settlement – Expansive clays, loose fill, or seismic activity (common in NZ) can shift the soil mass the wall is meant to hold.
- Deteriorated materials – Rotted timber, corroded steel, or crumbling concrete blocks reduce structural integrity over time.
- Undersized or incorrectly built wall – Walls built without engineering input may simply not have been strong enough for the job.
Assess the Situation Before You Start
Before touching anything, take a careful look at the wall:
- Measure the lean – Use a spirit level or plumb bob. A wall leaning more than 25–30 mm out of plumb is a significant concern.
- Check for cracking – Horizontal cracks near the base are especially serious; they indicate bending failure.
- Look for drainage issues – Are there weepholes? Are they blocked? Is water pooling behind or at the base of the wall?
- Check the wall height – Under the NZ Building Code, retaining walls over 1.5 metres in height generally require a building consent. Walls under 1.5 m may be exempt under Schedule 1, but you must confirm this with your local council — exemptions depend on site conditions, surcharge loads, and proximity to boundaries or structures.
Drainage: Fix This First
In most cases, poor drainage is the primary culprit. Even if you carry out structural repairs, they will fail again if water pressure is not relieved. Steps to improve drainage:
- Clear blocked weepholes (typically 75–100 mm diameter holes through the wall face, spaced every 1–2 metres).
- Excavate behind the wall and install or replace a agricultural drain (ag-pipe) wrapped in geotextile fabric at the base of the wall.
- Backfill with free-draining gravel (20 mm crushed rock is commonly used) rather than clay or compacted soil.
- Redirect surface water away from the top of the wall with grading or channel drains.
Repair Options by Wall Type
| Wall Type | Common Repair | DIY Feasible? |
|---|---|---|
| Timber sleeper | Replace rotted sleepers, install new deadmen | Possibly, for low walls |
| Concrete block / masonry | Rebuild section, improve drainage | Partially |
| Poured concrete | Engineer assessment required | Rarely |
| Gabion / rock | Re-pack stones, improve drainage | Yes, for minor lean |
| Segmental block (e.g. Keystone) | Rebuild with geogrid reinforcement | Possibly, low walls |
Timber Sleeper Walls
If deadmen (horizontal anchors running back into the bank) are missing or rotted, the wall has no resistance to overturning. You will need to excavate behind the wall, install new treated timber or concrete deadmen at regular intervals (typically every 1.5–2 m vertically and horizontally), and reconnect them to the face of the wall with galvanised bolts or rods.
Concrete Block or Segmental Walls
A wall that has moved significantly may need to be partially or fully demolished and rebuilt. Attempting to push a displaced masonry wall back into position without rebuilding is rarely effective and can be dangerous.
Building Consent and NZ Regulations
This is critical: if your retaining wall is over 1.5 metres high, or retains soil next to a boundary, driveway, or building, repairs that involve structural changes will likely require a building consent from your local council. Always check before starting work. MBIE Building Performance has guidance on what triggers consent, but your council has the final say.
For walls requiring engineering, you will need a Chartered Professional Engineer (CPEng) to design the repair solution. This is especially important in earthquake-prone areas — which covers much of New Zealand.
BRANZ also provides technical guidance on retaining wall construction and repair that is worth reviewing.
Safety First
Do not work directly in front of or behind a leaning retaining wall without propping or shoring it first. A collapsing wall can cause serious injury or death. If the wall is actively moving, keep people and vehicles away and call a professional immediately. Check WorkSafe NZ guidance on working safely near unstable structures.
When to Call a Professional
Call a licensed retaining wall builder or structural engineer if:
- The wall is over 1.5 metres high
- There is significant lean, cracking, or active movement
- The wall is near a boundary, building, or driveway
- You are unsure of the original construction method
- The wall retains soil near a slope or unstable ground
- A building consent is required
A qualified retaining wall specialist can assess the wall, design an appropriate repair, and carry out the work to meet the NZ Building Code. You can find experienced local retaining wall builders on tradedirectory.co.nz.
Licensed Building Practitioner (LBP)
