With over 35 years experience in the retaining wall industry, we know retaining walls better than anyone.

RWi know retaining walls!
RWi know retaining walls!

With over 35 years experience in the retaining wall industry, we know retaining walls better than anyone.

Below we have answered some commonly asked questions.

Below we have answered some commonly asked questions.

Who’s liable for retaining wall costs?

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.
The liability is still proportionate to each party. By combining and constructing a joint wall, BOTH parties will save.
The costs are allocated relative to each party’s requirement for walling, this can be determined by site plans.

Why do I need to know the Law 75S2(a-c) (the cut below 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.
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.</span
(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?

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.

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

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

  1. 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?”.
  2. 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!!.
  1. 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.)

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.

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.
It is still cheaper as the more we build at the one time, the more cost effectively we can construct all walls.
  1. There are cases where walls specified will not be required in the future, or walls can be minimised.
  2. Definitely seek advice from Retaining Wall Industries.

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.
After footings have been laid and BEFORE studwork.
Note: Some walls need to be constructed before earthworks.

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

When is the best time to complete a retaining wall?

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

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

(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?

  1. Concrete Sleepers are the best choice where room is an issue. Normally that is on boundaries.
  2. Where fencing needs to be erected on top of the wall, again concrete sleepers are the obvious choice.
  3. Where room is not an issue, you should consider either moss rocks or block wall structures.
  4. Cheapest wall structures are moss rocks, then concrete sleepers, then block and boutique walls (brick and commercial walling)
  1. There are many patterns and colours available in concrete sleepers. Ask Retaining Wall industries for our brochure.

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.

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

(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?

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.

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.

Drainage and Backfill.

  1. 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.
  1. Generally, no. Backfill with on-site soil is part of the construction process.

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.

If you have any further questions, give the office a call on (08) 8387 8900 and speak to one of our retaining wall experts.

With over 35 years of experience, Retaining Wall Industries (RWi) are Adelaide’s leading builder of Retaining Walls! Why Choose RWi as your Retaining Wall Builder?

RWi have been building retaining walls for over 35 years. Our experience and expertise has made us the industry leader.

RWi’s team of industry professionals and expert equipment are more than capable of delivering high quality wall works of any size and complexity.

RWi use only the most superior quality materials available on market. RWi’s work is backed by a 10 year structural warranty giving you extra piece of mind.

RWi will not be beaten on price. That’s the RWi price guarantee. RWi’s skilled estimators price all of our projects competitively with the intention to win!

Get in touch with RWi today!

Contact RWi today.

RWi – Retaining Wall Industries
6 Trizolpic Court, Lonsdale SA 5160
Phone: (08) 8387 8900
Email: walls@rwi.com.au

John Rowland
Ian Wilden