13.2 Retaining walls up to 1.5 metres depth of ground
A building consent is not required for a retaining wall in a rural zone if the wall is retaining 1.5 metres or less depth of ground and it includes ground water drainage in relation to the retaining wall.
The retaining wall must not support any surcharge or any additional load such as vehicles or buildings.
What the law says
Schedule 1 of the Building Act 2004
Exemption 20. Retaining walls
Building work in connection with a retaining wall that:
(a) retains not more than 1.5 metres depth of ground; and
(b) does not support any surcharge or any load additional to the load of that ground (for example, the load of vehicles).
How it works
This exemption does not apply to retaining walls that are subject to any additional load or surcharge, such as:
- vehicle driveways
- parking spaces
- swimming pools
- buildings
- other retaining walls
- sloping ground above the top of the retaining wall.
Also refer to section 13.3. Retaining walls not exceeding three metres depth of ground (exemption 41). This exemption covers building work relating to some retaining walls in rural zones as long as the design is carried out or reviewed by a Chartered Professional Engineer.
If the ground above the top of the retaining wall is only gently sloping, this may not be considered as ‘surcharge’. To determine the impact of the sloping ground and its pressure on the stability of the proposed retaining wall, you may wish to seek professional advice, for example, from a Chartered Professional Engineer.
If there is a fall of one metre or more from the retaining wall, you may be required to install a safety barrier (under Building Code clause F4 – Safety from falling). Factors to consider include the purpose or use of the retaining wall, how accessible it is, and whether it is frequented by young children.
What is exempt
- A builder plans to reconstruct an earthquake-damaged timber retaining wall that is less than 1.5 metres high. There is no surcharge on the retaining wall, so a building consent is not needed.
- A motel owner decides to terrace the motel’s uphill sloping section by building three 1.2-metre-high concrete crib retaining walls to create three level platforms, each of which will be planted. As there will be sufficient horizontal separation between each of the retaining walls so that no surcharge load will be imposed on a lower wall, no building consent will be needed.
Retaining walls without surcharge and no greater than 1.5 metres high – no consent required.
What needs consent
- An owner wishes to form a level platform for a garden below a neighbour’s driveway. To do this, she intends to construct a 1.2 metre high retaining wall. As the proposed retaining wall is subject to a surcharge from the neighbour’s vehicle driveway, it will require a building consent.
- A retaining wall ranges in height from 900 millimetres to 1.8 metres. The part of the retaining wall that exceeds the maximum allowable height of 1.5 metres will require a building consent.