Retaining Wall Checklist - Free Download

Approval, subsoil drainage and quote checks

Every item has a reason attached, because a checklist of labels is easy to tick and easy to misunderstand. The first nine items settle whether your wall is regulated building work. The next three cover the subsoil drainage that decides whether it lasts. The last four are the questions that make two quotes comparable.

Method and sources

This checklist is not an assessment and it does not tell you whether your wall is approved, compliant or safe. It is a set of questions, drawn from published requirements, that you can answer yourself before you speak to anyone. The approval items come from the Sunshine Coast Regional Council position published at sunshinecoast.qld.gov.au, the Sunshine Coast Planning Scheme 2014 Landslide Hazard and Steep Land Overlay, and the Queensland exemption conditions. The drainage items come from QDC NMP 1.7. The licensing item comes from the Queensland Building and Construction Commission at qbcc.qld.gov.au, which sets licensing by the value of the building work rather than by wall height. The assumption behind every item is that a private building certifier makes the decision, not this page.

1. 1

   Measure the total height from the bottom of the retained face

   Height is measured from natural ground level at the low side, not from where you are standing. Measuring from the top is how a 1.4 metre wall gets described as a 700 millimetre one, and it puts the whole approval question on the wrong footing.

2. 2

   Check whether the finished ground behind the wall will be raised

   Fill placed behind the wall counts toward the retained height. A low wall with 400 millimetres of fill behind it is not a low wall any more.

3. 3

   Identify anything sitting inside the zone of influence behind the wall

   A driveway, shed slab, pool, parked vehicle or another wall is a surcharge load, and a surcharge generally means building approval is required at any height at all. This is the single most commonly missed trigger.

4. 4

   Measure the distance to the nearest building or other retaining wall

   Within 1.5 metres of a building or another retaining wall, building approval is generally required even for a low wall with nothing on top of it.

5. 5

   Check whether the wall forms part of a pool barrier

   A wall that is part of a pool fence has to satisfy pool safety requirements as well as structural ones, and that is a separate approval trigger with its own consequences if missed.

6. 6

   Add any fence or screen height to the wall height

   Where a fence or screening sits on top of a retaining wall, the combined height from natural ground level matters, and 2.0 metres is the threshold where building approval generally applies.

7. 7

   Work out whether the wall will exceed 2 metres anywhere along its run

   Sunshine Coast Regional Council acts as a concurrence agency, so a wall over 2 metres needs council approval in addition to building approval. On a sloping run the tallest point governs.

8. 8

   Check whether the block sits inside the Landslide Hazard and Steep Land Overlay

   The Sunshine Coast Planning Scheme 2014 defines steep land as slopes of 15 per cent or greater and requires a slope-stability assessment for sites in the overlay. Hinterland and escarpment blocks are the ones most likely to be affected.

9. 9

   Assume a building permit is required until you can rule it out

   The council states you must have a building permit before construction, modification or repair of most retaining walls. Starting from that assumption is safer than starting from the generic under-a-metre rule, and a private building certifier makes the final call.

10. 10

    Ask whether the job includes an ag drain, aggregate and geofabric

    QDC NMP 1.7 requires subsoil drainage behind retaining walls, and drainage is priced along the wall rather than by face area, so it can be dropped from a quote without changing the headline rate.

11. 11

    Confirm where the drainage outlet discharges

    Water has to reach a lawful discharge point inside your own boundary and cannot be concentrated onto a neighbour's land. On flat ground the outlet is a genuine design problem, and it sometimes moves the wall.

12. 12

    Ask what backfill material goes behind the wall

    Free-draining aggregate behind the wall and site spoil pushed back into the trench produce completely different outcomes. The second one holds water against the wall and is the cheapest way to shorten its life.

13. 13

    Ask whether the price is labour only or supply and install

    Both are commonly quoted and the two numbers are not comparable. Comparing one against the other is how a quote looks thousands cheaper without being cheaper at all.

14. 14

    Ask for excavation, disposal, engineering and access as separate lines

    These are the items that make two quotes at the same square metre rate land thousands apart. Itemised, they can be compared. Bundled into one figure, they cannot.

15. 15

    Ask for Form 15 and Form 16 by name on an engineered wall

    Form 15 certifies the design and Form 16 follows on inspection, typically issued by an RPEQ. Knowing the names means you can ask for the documents and check you actually received them.

16. 16

    Confirm the contractor's licence covers the value of the work

    QBCC licensing is triggered by the value of the building work rather than the height of the wall, so a low wall can still be licensed work. Checking the licence against the job value is worth the two minutes.

General information only. A private building certifier and Sunshine Coast Regional Council decide what your wall requires, and an RPEQ does any structural design. See the disclaimer.