Retaining walls provide a number of functions making them a popular choice for Kiwi properties. A retaining wall can provide more space to tier or terrace a garden - useful in properties built on a slope (lots of retaining walls in Wellington). A smaller retaining wall between knee and shoulder height gives you a new easy-to-access level on which to put soil down and grow plants. Tending to a garden raised up like this can be easier on the back which is a bonus, too.
Retaining walls also provide runoff for water, helping to support effective drainage and reduce the amount of pooling during rain or watering. Sometimes the main motivation for a retaining wall is the visual appeal, helping to make a garden look clean and well landscaped.
One of the first things to establish is what type of retaining wall you actually want to build. This will be important to know before you approach the council about consent. Get an idea of the size, positioning and materials first, then you can go about getting it built.
A timber retaining wall is a good combination of strength, nice appearance and DIY-friendly. Other retaining materials include brick, stone and concrete. These each have their own aesthetic and functional benefits, but timber is likely the most affordable and straightforward to put in. If you want a weekend-long project, we’d usually suggest timber, provided you have the right tools and do proper planning first.
We’ll assume we’re building a timber retaining wall for this article, but keep an eye out for future content about other types too.
If you’re going for something quite modest you might not have to get consent - according to Building regulations you can build a retaining wall that retains up to 1.5 metres depth of ground, provided it does not support any additional load (eg a vehicle on top). Unconsented work can get you into trouble down the line, so it’s best to run your plans past your local council and make sure your retaining wall plans comply with local guidelines.
You will need to make sure the entire retaining wall, including associated drainage, fill and wall are all located on your property, well within the boundary line shared with your neighbour. Going over the boundary is serious and can become a costly legal issue. Play it safe and confirm everything is on your side of the line.
Speaking of drainage, you need to think carefully about this and work out how this will be incorporated into your plan. Inadequate drainage presents a very real risk of the wall falling apart from water-logged footings. Poor drainage can even impact other parts of the property and worse still your home. Again, if you aren’t sure, seek advice from an expert for peace of mind.
Now it’s time to draw an actual plan with some careful measurements. How tall should the wall be, do you want square or round posts, where is drainage placed, what is the depth of your wall? If the wall is not overly complex in design and size, you may find drawing your own plans easier. Otherwise you can get help from an architect. You may also be able to purchase some plans that can be modified slightly to fit your property. Whichever direction you go, have the finished product well-defined prior to starting construction.
If your retaining wall project is small and you have a good plan, you might want to try building this yourself. If you’re missing tools to get it done, remember you can hire top quality equipment from us, so don’t feel like you need to rush out and buy expensive power tools! We get behind Kiwis who’re keen to give their own projects a go. A landscaping project that you’ve done first-hand isn’t just satisfying, but could save you a bit of money in the process. Taking a bit of time to hire the right tools for the job can save you time and effort when it comes time to build your retaining wall. A posthole borer can speed up digging holes (and save your back) and a concrete mixer can make light work of your concrete mix so you can get the job done smarter.
For larger or multi-tiered retaining walls, we’d recommend getting a qualified, experienced engineer to design and advise you. Depending on the complexity you may get some help with the actual build too. You’ll know if the project’s pushing your own capabilities - so best to seek some help and avoid big problems later.
The best way to avoid issues with this project, is to involve your local council. They can advise you on consent requirements and ensure you don’t proceed with a project that will cause you or neighbours problems later. Chatting to the council doesn’t necessarily mean you’re asking for consent, and they’re used to fielding questions around DIY projects.
There’s a number of things you’ll need to have for this timber retaining wall project:
Fencing and/or decking timber (depending on the design)
Concrete for fixing posts
Nails for building the timber wall
Draining materials like pipe and fittings
Hammer or nail gun
In some cases, a mini excavator can help speed up the job (will depend on your site access)
Your retaining wall project will differ depending on where it’s positioned, the size, and materials. Below are some common steps involved in building a timber retaining wall:
If working on sloped or uneven land, level the ground where you plan on putting in your posts
Mark out where your posts will go and dig holes to depth with a post hole borer Note: If your retaining wall is over 1m you will need to angle your posts.
Brace the posts inside the holes with a concrete block or layer or scoria rock ensuring that posts are plumb or at the desired angle, using a string line for guidance.
Mix concrete and pour concrete around the braced posts to secure them in place, ensuring that the posts are plumb as the concrete is added and don’t move from the guide. Allow to set and remove bracing when dry.
Fix boards to the back of posts with galvanised nails or screws, starting from the bottom up. Use a level string line along the bottom to ensure your first row is straight and you are working horizontally between boards. Stagger boards at the bottom if your retaining wall is on uneven or sloped ground. Ensure joints are hidden behind posts.
Cut posts to height when all boards are attached and seal with timber preserver on top.
Install drainage scoria rocks at the base of the retaining wall along the back before laying a drain coil along the wall, then top up with scoria rock and cover with topsoil
Seal or paint your timber retaining wall if desired.
Once you’ve built your wall you can start adding features to add to the presentation. You might already know exactly what you want to add to it before building. Here’s some ways you might utilise a retaining wall:
Plant seed or lay ready-made lawn for a new grass area in your garden.
Put down soil and plant some of your favourite flowers and bushes.
Spread bark chips and line trees for a smart professionally landscaped look.
Add new spaces to your garden by partitioning off terraces with light fencing like a trellis.
Use the new terrace for a secondary entertaining area with some outdoor furniture.
We’re sure you’ve got some big plans - a retaining wall might even be part of a broader landscaping project.
We know what tools you’ll need for a retaining wall project. Check out our range and order online or contact your local branch today for a chat. Our Fencing, Decking & Retaining section has some handy guides for some of the main jobs involved in building a retaining wall.