Retaining walls

Retaining walls can be categorised by material:

• timber
• concrete, concrete blocks, shotcrete
• brick or stone masonry
• boulder.

or by type of construction such as:

• sleeper wall (timber or concrete)
• crib wall (timber or concrete)
• reinforced walls (concrete or shotcrete)
• weight walls (boulder or mass concrete or masonry).

• Timber walls are vulnerable to vermin infestation (white ants) and weathering.
• Dampness causes timber to rot significantly while it increases the strength of young concrete and lime mortar.
• Boulder retaining walls and crib walls occupy large spaces.
• The stability of a boulder retaining wall is highly dependent upon the skill of excavator operator in choosing the right boulder for the right location.
• Footings for reinforced concrete or reinforced concrete block retaining walls can be extended either in front or behind the wall. This can be extremely helpful in circumstances where space is limited in one direction such as retaining walls at property boundaries.

Seek advice from a Registered Professional Engineer of Queensland (RPEQ) to find the most suitable retaining wall for the conditions on your property.

You do not need to obtain a building approval if the wall satisfies all three following conditions:

• the retaining wall has no surcharge loading (for example, a driveway above the retaining wall will impose a surcharge loading on the retaining wall)
• the retaining wall is not located within 1.5 metres of a building or another retaining wall
• the height of the retaining wall measured from the adjacent natural ground level is less than one metre.

If the retaining wall cannot satisfy all of the above conditions, it is considered an assessable development requiring a building approval.

If you construct an assessable retaining wall without first obtaining a building approval you have committed an offence against the Building Act 1975. There are heavy penalties for offences against this legislation.

You should take the following steps prior to building a retaining wall to avoid future problems:

1. consult with an engineer, an architect, or a building designer to prepare a plan showing the location of the retaining wall on your property
2. consider at least a 200 millimetre clearance between the property boundary line and the closest part of the retaining wall (usually the footings or drainage media)
3. ensure that the wall is not within two (2) metres of City underground services (sewer main, stormwater pipe or water supply main pipe)
4. engage a Registered Professional Engineer of Queensland (RPEQ) to select, design and certify the most suitable type of retaining wall for the site
5. advise the RPEQ if you are planning a another structure that may impose a surcharge loading on the wall (for example, driveway or building loads adjacent to wall)
6. obtain a copy of the engineer-designed section for the wall signed and certified by the RPEQ
7. obtain a building approval if a surcharge loading is imposed on the wall or the height of the wall is one (1) metre or greater, or the wall is located within 1.5 metres of a building or another retaining wall
8. a building approval can be obtained from the City or from a suitably qualified private building certifier prior to construction of the wall
9. engage a registered builder to build the wall under the supervision of the RPEQ
10. obtain inspection certificates from the RPEQ for the construction of the wall at different stages (excavation, reinforcement, subsoil drainage and final)
11. obtain a final certificate from the private building certifier.

Note: Items 7, 8 and 11 are not necessary where the retaining wall is accepted development.