Yes, as a homeowner you can — and should — carry out regular visual checks of your retaining wall. However, a DIY inspection has real limits. Retaining walls hold back significant volumes of soil and water, and a failure can cause serious property damage or injury. Knowing what to look for helps you catch early warning signs, but a qualified building inspector or geotechnical engineer should assess anything that concerns you.
Why Retaining Wall Inspections Matter
Retaining walls are subject to considerable lateral earth pressure, especially after heavy rain when saturated soil becomes much heavier. New Zealand's varied terrain, seismic activity, and high-rainfall regions (particularly the West Coast, Northland, and Wellington) make wall stability a genuine safety issue. Under the NZ Building Code, retaining walls must be designed and built to safely resist the loads placed on them — including earthquake loads in many parts of the country.
Walls over 1.5 metres in height typically require a building consent, and walls over certain heights or retaining cuts near boundaries may need to meet specific engineering requirements. Always confirm consent requirements with your local council, as rules vary.
What You Can Check Yourself
A careful homeowner can perform a useful visual inspection. Walk the full length of the wall and look for the following:
Signs of Movement or Structural Distress
- Leaning or tilting — any noticeable lean away from the retained soil is a serious warning sign
- Bulging or bowing — a curved or belly-shaped face suggests the wall is being pushed outward
- Cracking — horizontal cracks in a concrete or block wall are particularly concerning, as they indicate bending stress; vertical or diagonal cracks may signal settlement
- Separation at joints — gaps opening between blocks, timbers, or panels
- Displacement of individual blocks or timbers — elements that have shifted out of alignment
Drainage Problems
- Weep holes blocked — weep holes (small openings near the base of the wall) should be clear and draining freely; blocked weep holes allow water pressure to build up behind the wall
- Waterlogging or pooling behind or at the base of the wall
- Staining or efflorescence (white salt deposits on concrete or block) — a sign of ongoing water movement through the wall
- Erosion at the base — soil washing away from the toe of the wall undermines its footing
Vegetation and Surroundings
- Tree roots growing into or behind the wall can exert significant pressure over time
- Heavy plantings or structures added above the wall since it was built may have increased the load beyond the original design
- Changes to drainage patterns nearby — new paving, downpipes, or landscaping that directs more water toward the wall
How to Document What You Find
Take dated photos of any cracks, movement, or drainage issues. Measure crack widths with a ruler and note them down. Check again after heavy rain — if cracks widen or the wall moves further, that tells you the problem is active. This documentation is valuable if you later engage a professional.
Understanding the Limits of a DIY Inspection
A visual inspection cannot tell you:
- The condition of the wall's footing or foundation below ground
- Whether tie-backs, deadmen anchors, or reinforcing (if present) are still intact
- The soil type and drainage behind the wall
- Whether the wall meets current NZS 3604 or engineering standards
- The wall's seismic performance capacity
BRANZ research highlights that many older retaining walls in NZ were built without formal engineering input and may not meet current standards — particularly for earthquake loading.
When to Call a Professional
Contact a licensed building inspector, structural engineer, or geotechnical engineer if you notice:
- Any leaning, bulging, or active cracking
- Cracks wider than approximately 3–5 mm (as a rough guide)
- Evidence the wall has moved since it was built
- Blocked drainage that you cannot easily clear
- The wall is over 1.5 m high and showing any distress
- The wall is near a boundary, driveway, or structure
- You are buying a property and want a pre-purchase assessment
For walls showing significant movement, do not wait — a failing retaining wall can collapse suddenly, especially during or after heavy rain. Keep people away from the area and seek professional advice promptly. You can find qualified local building inspectors and engineers on tradedirectory.co.nz.
If any remedial work requires a building consent, the work may need to be carried out or supervised by a Licensed Building Practitioner (LBP). Check with your local council before starting any repair or reconstruction work.
Safety Note
Never stand directly below or at the base of a wall you suspect is unstable. If a wall appears to be in imminent danger of collapse, treat the area as unsafe, keep others away, and contact a professional immediately. WorkSafe NZ provides guidance on managing risks from unstable structures.
Licensed Building Practitioner (LBP)
BCITO Qualified
