Retaining walls on subdivisions: when a consent is required
Ask around a site and someone will tell you retaining walls under 1.5 metres do not need a consent. That is half of the rule, and the half people leave out is the half that catches most subdivision retaining.
What the exemption actually says
Schedule 1 of the Building Act 2004, Exemption 20, covers building work in connection with a retaining wall that:
retains not more than 1.5 metres depth of ground; and
does not support any surcharge or any load additional to the load of that ground.
Both conditions have to be met. A wall retaining a metre of ground is not automatically exempt. If it is carrying an additional load, the exemption does not apply no matter how low it is.
The 1.5 metre figure is the half everyone remembers. The surcharge test is the half that decides most real sites.
What surcharge means in practice
Surcharge is any additional load bearing on the retained ground beyond the weight of the ground itself. On a development site that is common rather than exotic:
A driveway or accessway running above or beside the wall, carrying vehicles
A building, foundation or structure within the zone of influence behind the wall
Sloping ground above the wall, which adds load beyond level ground
Stored material, fill or plant standing behind the wall
A second wall above, or a boundary structure loading the retained mass
On a subdivision, retaining is usually there precisely because something is being built or driven on above it. That is why so much subdivision retaining needs consent regardless of height.
Why retaining and drainage are the same conversation
Retaining walls fail for two reasons: they are under-designed, or the water behind them was never dealt with. Water in the retained ground adds hydrostatic pressure that most walls are not designed to carry, which is why drainage behind a wall is a structural requirement rather than a refinement.
A properly built wall has drainage metal and a subsoil drain behind it, wrapped and taken to a legitimate discharge. That is the same discipline covered in subsoil and land drainage. Skipping it is the most common reason a wall moves.
Where retaining sits in the civil package
On a subdivision, retaining is bound up with the earthworks: the cut and fill design determines where walls are needed and how high, and the wall determines what can be built above and below it. Treating retaining as a separate later trade tends to produce walls in awkward positions and levels that do not resolve.
It sits alongside the wider works covered in subdivision civil works and earthworks.
Resource consent is a separate question
Building consent is about the structure. A retaining wall may also raise district plan questions through earthworks volumes, height, boundary effects or landform change, which is a resource consent matter rather than a building one. The two run on different tracks and both need checking.
Questions we get asked
Is a retaining wall under 1.5 metres always exempt?
No. It must also not support any surcharge or additional load beyond the weight of the retained ground. Both conditions must be met.
What counts as a surcharge?
Any additional load on the retained ground: a driveway or vehicles above, a building or foundation within the zone of influence, sloping ground, stored material, or another structure loading the retained mass.
Does a wall holding up my driveway need consent?
A driveway carrying vehicles is an additional load, so the Schedule 1 exemption would not apply. Confirm with your council.
Why does my wall need drainage behind it?
Water in the retained ground creates hydrostatic pressure the wall is generally not designed to carry. Drainage behind a wall is structural, not optional.
Do I need resource consent as well?
Possibly. Earthworks volumes, height and boundary effects can trigger district plan requirements separately from building consent. Both need checking.
This page is general in nature and is not legal or engineering advice. Confirm consent requirements with your territorial authority and wall design with a chartered engineer.
Draeinail Construction has been putting drainage in the ground across Auckland and the Franklin district since 2006. Request a quote or call Darryn Muir on 021 271 0035.
