As a general rule in NSW, retaining walls higher than 600 mm require council or CDC approval, and that approval requires a structural design by a qualified engineer. Even below 600 mm, an engineered design is wise wherever the wall supports a driveway, pool, building footing or a neighbour's property.
The detail most owners and landscapers miss is surcharge — the extra load applied to a wall by whatever sits above it. A 1 m wall holding back flat garden bed and the same wall with a driveway behind it are two very different structures. Ignoring surcharge is the most common cause of leaning and failed walls we inspect.
Good retaining wall design covers the stem and footing, but also global stability, subsoil drainage (ag-line and gravel behind the wall, weepholes where needed) and the interaction with boundaries and existing structures.
We design and certify concrete block, reinforced concrete, concrete sleeper and timber walls, and we can also inspect and report on existing walls showing signs of distress.