Heavy rain events can put enormous pressure on retaining walls, causing cracking, leaning, bulging, or even full collapse. If your retaining wall has been damaged, it's important to act carefully and methodically — both for your safety and to protect your property from further harm. Here's what to do.
Step 1: Stay Safe First
Before you go anywhere near a damaged retaining wall, assess the situation from a safe distance. A wall that is leaning, bulging, or has partially collapsed could fail completely without warning, especially if the ground behind it is still saturated. Keep children and pets well away from the area.
If there is any risk of a landslip or slope failure — particularly on steep sections — contact your local council immediately. Many councils have emergency response teams for storm damage. WorkSafe NZ also provides guidance on managing hazards around unstable structures.
Step 2: Document the Damage
Once it is safe to do so, photograph and video the damage thoroughly. Capture:
- Cracks in the wall face or capping
- Leaning or bowing sections
- Displaced or missing blocks/timbers
- Drainage issues — blocked weepholes, saturated soil, water pooling behind the wall
- Any movement in the soil or garden above the wall
This documentation is valuable for insurance claims, council notifications, and getting accurate quotes from retaining wall builders.
Step 3: Check Your Insurance
Contact your home and contents insurer promptly. Storm and flood damage to retaining walls is often covered under home insurance policies, but this varies. Provide your photos and a description of the event. Your insurer may send an assessor, so avoid doing major repairs until you have their sign-off — otherwise you could affect your claim.
Step 4: Understand What Might Have Gone Wrong
Most retaining wall failures after rain come down to a few common causes:
- Poor drainage — water builds up behind the wall (hydrostatic pressure) and pushes it over
- Blocked or absent weepholes — these small holes let water escape through the wall face
- Undersized or deteriorated wall — the original wall may not have been designed for the load
- Root damage — tree roots can displace blocks or timbers over time
- Soil saturation and surcharge — heavy, waterlogged soil is much heavier than dry soil
Understanding the cause is just as important as fixing the visible damage. A good retaining wall builder will investigate the root cause before recommending repairs.
Step 5: Know When You Need Building Consent
This is critical. In New Zealand, retaining walls are regulated under the NZ Building Code, and many repairs or replacements will require a building consent from your local council.
As a general guide:
| Wall Height | Likely Consent Requirement |
|---|---|
| Under 1.5 m (no surcharge) | May be exempt under Schedule 1 — check with council |
| 1.5 m or over | Building consent likely required |
| Any height with surcharge (e.g. driveway above) | Consent likely required |
| Any height near a boundary | Check with council |
Always confirm with your local council before starting work. Schedule 1 exemptions under the Building Act 2004 can apply to some low retaining walls, but the rules depend on height, ground conditions, surcharge loads, and proximity to boundaries or other structures. MBIE Building Performance has detailed guidance on building consent requirements.
Step 6: Address Drainage as a Priority
Even before full repairs begin, try to improve drainage if it is safe to do so. This might mean:
- Clearing blocked weepholes with a piece of wire or rod
- Diverting surface water away from the top of the wall
- Checking that any ag-pipe (agricultural drainage pipe) behind the wall is not blocked
Good drainage is the single most important factor in retaining wall longevity. BRANZ has useful technical resources on drainage and earthworks around buildings.
Step 7: Get Professional Quotes
For anything beyond very minor cosmetic repairs, get at least two or three quotes from qualified retaining wall builders. A reputable builder will:
- Inspect the site thoroughly, including the soil and drainage
- Advise whether a geotechnical engineer or structural engineer is needed (often required for consent applications)
- Explain what consents are required and handle the paperwork
- Provide a written quote and timeline
You can find qualified local retaining wall builders on tradedirectory.co.nz.
When to Call a Professional
Call a professional retaining wall builder or engineer immediately if:
- The wall is leaning, bulging, or has collapsed
- There are cracks wider than a few millimetres or signs of ongoing movement
- The wall is over 1 m tall and has sustained visible damage
- There is a driveway, building, or other structure above or near the wall
- You notice soil movement or cracking in the ground above the wall
- You are unsure about the cause of the damage
Retaining wall failures can escalate quickly, especially on sloped sections. This is not a situation to leave and hope for the best.
Licensed Building Practitioner (LBP)
