A lot that’s ready to build is attractive to prospective buyers. Every unknown cost adds uncertainty. A lot that’s level and needs no site works removes one risk. To achieve this on sloped sites, estate developers often install freestanding retaining walls on lot boundaries.
Well done, retaining walls can add substantial value to a lot’s sale price. Done poorly, they can reduce value. This bulletin explores the options for freestanding retaining walls for residential lots.
A hillside with benched house sites retained with concrete sleeper walls. This saves each lot owner installing walls.
Retaining walls come in four broad types:
- Retaining walls on lot boundaries, often surmounted by a fence. These walls are typically installed by the estate developer to create a benched lot, that is, one with a flat pad for a house.
- Retaining walls near or on a lot boundary, typically installed by the lot owner to achieve benching, especially where a battered slope would take up too much of the lot.
- Retaining walls for raised garden beds or landscaped terracing.
- Part of a house or other structure, such as dropped edge beams, either below or above the ground level.
This bulletin discusses the first three types, freestanding retaining walls that are separate from buildings.
In side and rear yards, retaining walls are only seen by the lot occupant and possibly the immediate neighbours. For these locations, timber or plain concrete sleeper retaining walls with metal uprights are usually the cheapest option.
Retaining walls in front yards are seen from the public realm. In these locations, timber or concrete sleeper walls are usually considered unsightly and are often prohibited. Instead, a design code may require more attractive and more expensive materials, such as masonry, rendered blockwork, split faced blocks, stone, or textured sleepers.
Types of wall
Purely functional retaining walls are suitable for those areas of a lot that are not visible from the public realm. These are typically timber or concrete sleeper walls with posts of timber or steel. A simpler look can be achieved with timber walls by bolting the sleepers onto timber posts hidden behind the sleepers.
Post types for sleeper retaining walls.
Retaining walls suitable for front yards, where they will be seen from the street, can be made from materials such as stone, face brick and rendered masonry. These walls don’t need posts, and can be curved.
The tables below show different types of retaining walls and their relative cost.
Functional and cheap walls include plain or natural coloured sleepers with visible posts to hold them in place.
Average appearance walls add some visual texture. Many of them can hide the posts or do not have posts.
High quality appearance walls have some finer grain details and hidden or no posts.
Developer built walls
Developer built walls are installed by the estate developer to provide a bench on which the house can be constructed. This reduces the site costs for the future lot owner. These walls may retain excavated soil, fill, or a combination of cut and fill.
Concrete sleeper walls with metal uprights are often used as they are cheap and long lasting. Sometimes they are only used at the rear of lots, where they will be hidden from public view when the houses are built. Walls built in the front yard, where they will remain in public view, may be built with more attractive materials, such as stone. These walls are also more expensive.
A lot with a rock retaining wall at the front and a concrete retaining wall at the rear.
High retaining walls are both expensive and present an unattractive view to the occupant of the lot below them. Careful design of the layout of the lots and streets can sometimes avoid this, as can requiring houses to be built on a slope, rather than benching the lot.
On gentler slopes, the estate developer may decide to leave the benching and retaining walls up to the future lot owner.
A high developer-installed retaining wall surmounted by a fence. This wall is both expensive to build and an ugly outlook for the occupants of the lower lot.
Lot owner installed walls
A lot owner may install retaining walls to bench a house site or for landscaping. Most design codes require these walls to be less than one metre high. Where more than one wall is built to retain a higher slope, the design codes usually require the walls to be separated by garden beds.
Concrete sleeper retaining walls used for terraced garden beds on a cross sloped lot.
Design standards
If retaining walls are visible from the public realm, retaining walls should present an attractive appearance to the street.
“A retaining wall at the front boundary must be no higher than 1 m.”
“Retaining walls must be at least 1.5 m apart, with the space between used as a garden bed.”
“If a retaining wall is visible from the public realm, it must be made from grey split-face concrete blocks.”
Retaining walls on or close to lot boundaries may cause structural problems on the neighbouring lot, allow overlooking, or present unattractive views. The following standard can help avoid these problems.
“Freestanding retaining walls must be no more than 1 m above or below natural ground level, and at least 1 m from the lot boundary.”
