ARTICLE Carolyn Brooke
While retaining walls have always had a place in the landscaping arena, gone are the days of them having to be unattractive or boring. With the likes of real-stone panels, gabion cages and modular concrete systems available, adding a retaining wall can be an opportunity to visually improve an outdoor area.
Aside from the desired look, planning the style of a retaining wall you want will largely come down to what is being retained, your budget and soil conditions. Most important, regardless of whether you opt for stone, concrete or timber, is to establish if council consent and/or engineering design is required.
People often overlook building consents for retaining walls, but when dealing with land stability you want to get it right - you certainly do not want to be held responsible for damage to other people’s property due to an inadequate retaining wall.
Walls less than 1.5 metres high retaining garden areas generally do not require consent but any wall (regardless of height) bearing an additional load such as a driveway, building or carport will most likely require consent and possibly engineering design. It is always best to check first.
Good drainage is another key consideration as water build-up can compromise the wall’s structure and damp soil can cause it to move. Always seek advice when DIY building and be sure to check where pipes and cables to the house are located before you start digging posts.
How much does a stone-clad retaining wall cost?
Real-stone cladding can bring outdoor areas alive without the cost, time and hassle involved in building a full stone wall.
An existing timber, block or brick wall does need to be in place but from there it’s relatively easy for the stone-clad sheets to be attached.
Options include schist-clad panels or individual stone pieces (natural stone cut thin) which have been glued on to a fibre-cement sheet. The panels are pieces of natural stone glued together to form 600mm by 150mm modular sheets allowing for faster installation than the individual pieces.
Real-stone cladding costs from around $1,950* installed, keeping in mind a block or timber wall needs to be in place first. Artificial stone panels are also an option.
“It’s hard to beat the beauty of natural stone", says Zones Landscaping specialist Rose Bridge. "The main reasons people choose natural stone cladding are for its unique textures and tones, durability and versatility. Homeowners can choose from an abundance of types, colours and formats that suit their tastes and complement other materials around the property, such as timber and concrete. Because of their timeless, aesthetically pleasing qualities, and extreme sturdiness, natural stone walls can add real value to any property.
"The cost, however, can be prohibitive. Natural stone-clad walls tend to be more labour intensive and complex to build as they require structural substrates. It’s really important that they are built by an experienced professional to avoid problems that can be caused by poor installation, such as trapped moisture. In addition to the labour and material costs, sealing stone-clad walls for protection is highly recommended post-installation."
Cost for a stone-clad retaining wall
Starting from $1,950* per metre, installed (includes project management and GST)
How much does a gabion retaining wall cost?
Gabion stone walls are an attractive and functional gravity retaining wall system made from galvanised steel mesh filled with stone, brick or concrete.
"Whilst Gabion walls are more commonly used for industrial purposes, they have become increasingly popular in residential settings for a number of reasons", says Rose. "The combination of wire and stone offers an adaptable and contemporary look in the right outdoor space, without the costs associated with other stone walls. Gabion walls can be built to any size and custom-designed to be as decorative or practical as required. They are not only strong and incredibly durable but are also cost-effective and easy to install as they don’t require masonry or skilled labour. Once in place, they have the added benefit of natural drainage and require very little maintenance."
A gabion wall doesn’t need to be dug more than about 100mm into the ground and sometimes can just sit on top of the ground. A concrete foundation is not usually required.
Gabion walls can be a good solution in hard soil or clay where timber piles will be difficult. The wall’s thickness needs to be half the height so gabions are not very well suited to small sections where houses are very close to boundaries.
GabionNZ gabion baskets start from $43.06 for a 500 x 500 basket, with prices rising to $186.78 for larger baskets. Professional installation, project management and GST included, this adds up to approximately $160 - $515+* per basket.
Cost for a gabion retaining wall
Starting from $160* per basket (includes installation, project management & GST).
How much does a concrete retaining wall cost?
Modular or segmented concrete retaining block systems are also gravity-based. Concrete retaining blocks are built upon a concrete foundation by stacking or interlocking.
Cameron Greig of Peter Fell says longevity is the key advantage with concrete. While wood is less expensive and a simple choice, its lifespan is much shorter. “Concrete might cost a bit more money in the beginning but then that’s it,” Cameron says.
“If you drive around suburbs like Remuera you’ve got these brick walls that have been there 100 years with a lifespan of 5,000 years.” He says aside from durability people also opt for concrete for the look.
The Firth Keystone retaining range offers the natural look of stone to match your home aesthetic. There is a range of options from small to large to suit the size of your project including styles for landscape walls, tree rings, lawn edging and gardens.
Curved walls can be built to suit any project allowing it to blend in with any landscape. The most popular blocks in the larger size is the Firth Compac IV or of medium size are the Firth Garden Wall and Firth Sedona Stone blocks, which all offer a choice of a modern straight face finish or a traditional tri-face finish.
The Ezi Wall blocks are the lightest and easiest option for the DIY-er with their easy to use interlocking system and come in a choice of three colours.
Depending on the concrete blocks used, a retaining wall made from concrete blocks could start from around $299* - $390*.
Another concrete option is traditional grey 300 by 150-millimetre blocks but it’s not a DIY type job as it involves steel and filling.
Cost for a concrete retaining wall
Starting from $299+* per metre. (Includes installation, project management + GST. Excludes plaster and prep work).
How much does a timber retaining wall cost?
Timber is most often the lowest cost options for retaining walls. While timber won’t have the same durability as stone or concrete, a well-built retaining wall should look good and stay strong for decades.
Mitre 10’s building expert Stan Scott says pine is cheaper and quicker to use than other materials and a retaining wall can be built in a weekend.
“It’s easy to use, you can chop it up easily with a handsaw, skillsaw or chainsaw. It’s very quick to put up and relatively cheap.”
The integrity of a timber retaining wall relies on strong piles. Generally, piles go down as deep as the wall’s height. But once over 1.5 metres high, these dimensions’ increase, so, for example, a 3-metre retaining wall could need piles 4.5 metres down. Prices range widely for timber and the total cost will depend on the size of the boards used and how far the posts are spaced apart.
If paying a tradesperson to do the work then usually you need to double costs, although labour charges will vary depending on site accessibility and soil conditions.
“You might have to carry your tools right around the back of the house so half the day is just carrying materials. I did a job recently where the retaining wall was on solid rock and it took four hours to drill half a hole.”
Ask for quotes to be split out showing labour and materials so you can accurately compare them. There are different ways a retaining wall can be built and the cheapest quote is not always best.
Some contractors may undercut others to get the work but may exclude items from the quote. Showing your contractor photos of the desired finish you seek is another good way to avoid surprises.
“Just because it’s a retaining wall doesn’t mean it shouldn’t look nice – owners need to be as clear as possible about what they want.”
Cost for a timber retaining wall
Starting from $510* per metre including installation, project management & GST.
This project estimate Carolyn Brooke by featured in Issue 010 of New Zealand Renovate Magazine. New Zealand's first and only magazine solely dedicated to home renovations.
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