Retaining Walls FAQ

Who’s liable for retaining wall costs?

How do I define who’s liable?

If you alter the level of the land by either excavation (cut) or building up of levels (fill), it is your responsibility to retain and pay for that retention.

What if I cut and my neighbour fills his land on a boundary?

The liability is still proportionate to each party. By combining and constructing a joint wall, BOTH parties will save.

What if the cut and fill are disproportionate?

The costs are allocated relative to each party’s requirement for walling, this can be determined by site plans.

Isn’t it 50/50 like a fence?

No, see above.

faq4

(LEFT) Clearly defined cut & fill situation, joint walling is recommended. Costs are shared and maximum room gained by each party.
(CENTRE) An example of a potential problem involving excavation and undermining. A joint wall would have been the better solution.
(RIGHT) A perfect example of a good joint wall project.

Why do I need to know the Law 75S2(a-c) (the cut below law)?

What is the Law?

The law was introduced to attempt to avoid situations where walls were constructed upon a boundary and neighbours developed their land, and in doing so excavated on the boundary next to and below an existing wall. In many cases this caused existing walls to fail, and expensive arguments as to liability and ability to maximise your use of land.

So how does this affect me?

The law requires that all people retaining fill upon a boundary require extra pier depth and wall design to accept a maximum 600mm excavation below the wall. Effectively that means if you have a 1.0 metre wall, you require the wall designed for 1.6 metres. To you, this means more steel, deeper piers, more concrete in those piers, and at times heavier steel. This can add at least 30% to the cost of the fill side walls relative to the cost of cut side walls.

What if either my contractor or I do not adhere to the Law?

If your wall fails due to excavation at a future time, you will be liable for the re-build. You will have no claim for a third party as you will have constructed an illegal walling specification.

faq6

(LEFT) Note the excavation under the existing wall. Extra depth piers were allowed in the upper wall and as such there was no problem with undermining. (RIGHT) Completion of the undermined wall. Note concrete backfill used for increased stability.

When do I need Council approval?

I always thought it was 1.0 metre and over.

Most councils are only interested in walls over 1.0 metre. However, when a wall and fencing have a combined height of 2.1 metres. Ie. A fence height of 1.8m and a wall height of 300mm is strictly to the building code. Check with your council to be sure. Annoyingly some councils ignore this.

What do I need to supply council with?

Engineering for your wall, 3 sets (from your engineer ).
A site plan clearly showing your wall’s position and heights, 3 sets (from your builder).
A certificate of title (from the Lands Titles Office).
Council Planning and Building Application fees (from your council).
H.O.W Insurance
C.I.T.B

Do I have to do this?

No, Retaining Wall Industries can handle all of this for you.

How long does council approval take?

Approval can take up to 12 weeks, with an average of 10 weeks, so be aware of time when working with your programming. See below “When is the best time to complete a retaining wall?”.
Talk to your builder and have wall specifications and approval sought at the same time as your house application. This can save you and your builder a great deal of time and inconvenience, not to mention cost!!.

Should I combine with neighbours on boundary walls?

A resounding YES!
Firstly, you will save money, particularly if you are retaining filling. Construction costs are less as you are building one wall, and not one each. Law 75/2/A-C is not applicable if the wall is approved from the neighbour retaining cut – even if there is, say 1.0 metre of cut and the neighbour has 1.0 metre of fill above that cut, excavation below the wall will not occur. (In some cases sewer trenching will need to be considered.)

faq8

All walls over 1.0 metre require council approval, and when on a boundary with a fence all walls with the combined fence and wall height of 2.1 metres and over will require council approval.

Working with neighbours on boundaries.

Who pays what?

The total cost is divided into the amount of fill or cut each is retaining. Retaining Wall Industries can work out the percentage of liability for you from plans supplied by both parties.

What if we don’t have adjoining walls?

It is still cheaper as the more we build at the one time, the more cost effectively we can construct all walls.

What if my neighbour is not ready, and their future works may impact on my wall requirements?

There are cases where walls specified will not be required in the future, or walls can be minimised.
Definitely seek advice from Retaining Wall Industries.

When is the best time to complete my walling requirements?

Access is always your enemy. Large equipment is required to construct retaining walls.
The best time is:
After earthworks to create your bench level and before the footing is excavated and poured.
OR
After footings have been laid and BEFORE studwork.
Note: Some walls need to be constructed before earthworks.

faq10

(LEFT) Concrete Sleeper boundary walls and moss rock retention combinations.
(RIGHT) Joint walls with neighbours save money and space.

When is the best time to complete a retaining wall?

What if I need to have a wall constructed before earthworks can be completed?

This can and does happen. Work closely with your builder and Retaining Wall Industries.

Won’t my wall be damaged or soiled during house construction?

Possibly. This can and does happen from time to time. We can wrap your wall in black plastic.

faq12

(LEFT) Construct retaining walls before studwork.
(CENTRE) This wall was completed before studwork was erected. It would have been impossible to construct this wall after studwork do to restricted access.
(RIGHT) Retaining Wall Industries are the specialists.

What choices do I have?

What choices do I have in regard to wall types?

Concrete Sleepers are the best choice where room is an issue. Normally that is on boundaries.
Where fencing needs to be erected on top of the wall, again concrete sleepers are the obvious choice.
Where room is not an issue, you should consider either moss rocks or block wall structures.
Cheapest wall structures are moss rocks, then concrete sleepers, then block and boutique walls (brick and commercial walling)

What are my choices with regard to colours and patterns of concrete sleepers?

There are many patterns and colours available in concrete sleepers. Ask Retaining Wall industries for our brochure or click HERE for some samples.

Can I have steps?

Yes, concrete sleepers have standard step modules for most colours and patterns.
For moss rocks, normally you use slate, flagstone or flat moss rocks. There are other alternatives, just ask us.

Can I select paint colour for the steel?

Yes, steel is normally coated with black bituminous paint, or hot dipped galvanised. Clients normally supply any colour paint they wish applied during construction.

faq14

(LEFT) Concrete sleeper and moss rock walling.
(CENTRE) Moss rock and slate flagstone steps.
(RIGHT) Two tiered concrete sleeper walling and steps.

What about fencing?

Can I place fencing on my wall?

Yes, however by doing so the engineering alters from a standard calculation. Retaining Wall Industries adopt the correct calculations and can include your fencing requirements in your retaining wall quote.

How is fencing attached?

We normally weld directly to the uprights or fix a plate upon which the fence will be attached.

Do I have to fix my fence to the wall?

No. In fact if your fence is not attached to your wall, it will help achieve a lower price for your wall, as engineering will not need to take this into account.

faq16

(LEFT) Conventional post and rail fencing.
(CENTRE) Decorative timber fencing.
(RIGHT) Weldmesh fencing.

Drainage and Backfill

Do I need drainage and backfill behind my wall?

Concrete Sleeper walls: Generally yes. Standard practice is a 90mm agricultural pipe laid in a gully created by a plastic membrane laid behind the wall. It is covered with 300mm of 20mm gravel, and then covered with on-site fill. (Where retaining fill the on-site fill is normally placed by your sitre contractor). Discuss requirements with Retaining Wall Industries.

Where there could be large areas of water running to your wall, we suggest gravel, 200mm wide, to the full wall height.

Do moss rocks need drainage and backfill?

Generally, no. Backfill with on-site soil is part of the construction process.

faq18

(LEFT) Stress fractures in concrete sleepers caused by heavy machinery compacting material behind the wall.
(RIGHT) Backfill disaster due to material being pushed into the back of the wall.
Don’t let this happen to you – see special note below.

Special Note:

Extensive damage to your wall can occur from incorrect placement of fill behind your wall. Material should be PLACED not PUSHED behind the wall. Pushing can result in sleeper displacement, cracking and failure.

Compaction should never be carried out above a wall; a void should always be left between the wall and material being compacted. Machinery should NEVER drive directly above your wall or within 1.5 metres of the wall.

Retaining Wall Industries has standard backfill practice sheets available to you upon request to hand to contractors.