5 Key Elements To Understanding Retaining Walls

2000 Years Of Retaining Walls

There are many different types of retaining walls, in which many will suit the type, height and materials based on design preferences and the type of ground that should be retained.

They can be built from a number of different materials like: stone, brick, block, steel, timber and more and it will often be the site that dictates what type of materials are to used.

There purpose is to retain the any lateral forces of dirt, water or other materials.

Retaining walls date back to the old roman times and since then have improved over time with different design and materials.

They have their practical uses, but are also a great choice to tidy up your section and can definitely improve the value of your home.

Retaining walls can turn a steep slope into a beautifully terraced back yard, creating a stepped style look.

They are usually back-filled with different gradients of material added for more durability and usually have proper drainage at the base of the wall.

Don’t Take Shortcuts With Retaining Walls

It’s important to note that the types of back fill material will play a large part in the success of a retaining walls life. If cheap or insufficient materials are purchased or even neglecting below grade elements, will end up costing more later on. If the base foundations start eroding and cause damage to nearby structures the cost to repair or replace a retaining wall can end up being far expensive than the initial cost of building the wall. So don’t take shortcuts is the message here.

You’ll see a lot of block retaining walls under the house on steep sections, as well as around the section. Block walls are normally for heavy duty retaining.

If we start by understanding what types of retaining walls there are and why they exist, it will give you a better understanding. You can use your judgement and common sense to figure if a retaining wall is either illegal, it’s purpose is for aesthetics … or is just there for practical reasons.


What Types Of Retaining Walls Are There?

There are only two principal types of retaining walls that exist, which are: 1. Cantilevered and … 2.  Gravity Walls.

Cantilevered walls are normally tied into a solid base, which provides strength

…and Gravity walls use their own weight to resist pressure from the soil behind them.

1. Cantilevered Walls

If you’re not sure what cantilever means; it’s a beam of any sort that’s anchored at one end to support a load and will usually come in the form of T shape or an L shape

Cantilever walls are for stabilisation either on a wide ‘T’ or ‘L’ shaped footing or vertical poles deeply concreted into the ground. They’re normally tied into a solid base, which provide the strength need to retain the earth.

Here are a couple of good example of cantilever effect!





2. Gravity Walls

Gravity walls describe exactly what they do – They are constructed of materials that are heavy enough to resist the forward pressure from the earth behind it, but are very limited to height due to the nature of the wall and materials. `
Some of the typical materials that can be used would be block and stone, or masonry,  which are the heavier materials used to weigh down on itself. It will be mostly slanted backwards, with most of the weight and thickness being at the bottom for stability and performance.


Image provided by BRANZ

Do I Need Council Consent For a Retaining Wall?


The Building Act 2004 Schedule 1 tells us that any construction of a retaining wall that is under the height of 1.5m high does not require a building consent as long as there is no surcharge (see left side example of 1st image above) or other load on top of the load of the ground it is trying to retain.

Regardless of whether the wall needs a consent or not it still must comply with the The NZ Building code, which says in really broad terms, that it must be constructed and designed in a way that will withstand normal pressures that it has been designed for as well as any further construction or alteration, throughout it’s lifetime.

If retaining walls do need council consent, they need to be designed by a registered engineer.

Common Terminology

5 Key Takeaways


    1. 1. Retaining walls have been around since the dark ages


    1. 2. They have improved over time with materials and design


    1. 3. There are two main types of retaining walls: Gravity walls and Cantilever walls – Gravity walls anchor themselves with heavy duty materials and gravity. Canitlever walls are fixed at one end in usually an L & T shape.


    1. 4. You need a council consent if the wall is over 1.5m and must be designed by a registered engineer.


  1. 5. If the wall is under 1.5m You need a consent, if there is any surcharge or other weight bearing load on top of the retaining wall