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![Builing a Retaining Wall - Your complete guide]({"1201":"/medias/sys_master/root/hba/hba/11865963331614/building-a-retaining-wall-banner/building-a-retaining-wall-banner.jpg"} "Builing a Retaining Wall - Your complete guide")
Building a Timber Retaining Wall
The Complete How To Guide to Building a Timber Retaining Wall
Retaining walls perform heavy and important work. Therefore high or complicated walls, perhaps supporting several metres of bank above a road or driveway, must be designed and constructed by experienced contractors. Retaining walls can also be used to terrace a slopping section, provide a levelled garden, flat lawn or paving. The retaining wall described here is less than 1.5M in height with post spacing set at 1.2M, and does not support any surcharge or load additional to that of the ground.
Notes About Building Consents
- In New Zealand retaining walls over 1.5M high require a building consent from the local body council.
- Walls lower than 1.5M but carrying extra loading on top, for instance a driveway, a building or a steeply sloping bank, also require a building consent.
- If you are in any doubt, consult your council for advice. Some insurance may be void if retaining walls are not constructed and signed off correctly.
- Locations which require a building consent may also need an engineer’s design certificate.
Retaining Wall Fundamentals
Good Footings or Foundations
While the whole wall has to be strong enough to support the load pressing against it, it’s the part below the ground that anchors it. No matter how sturdy the upper part of a wall is, if the footings or foundations are weak, there is nothing stopping it from falling over. Check with your council to determine if a geotechnical and structural engineering report is required.
Good Drainage Behind and/or Through the Wall
When soil or clay on a slope is waterlogged, it is practically unstoppable. Like jelly while it’s still liquid, you need a bowl to contain it, but after it’s set, it supports itself.
So one of the main tasks required of a retaining wall is to drain water out of the bank behind. If a wall doesn’t drain well, even previously dry earth in the bank will gradually become waterlogged until it finally pushes the wall over. Check regulations regarding water run off from drainage.
Materials
- H5 treated 200mm diameter posts – one every 1.2M of wall length.
- 150 x 50mm or 200 x 50mm H4 treated rough sawn or tongue & groove rails. Alternatively use 150mm half round trimmed rails.
- Free draining metal backfill (approximately 1/3M3 will be used for every metre of the retaining wall length).
- Concrete to set the posts. (Rapid set concrete will speed up the process).
- Nails – 100mm and 125mm or 150mm Hot-dipped galvanised.
- Timber preservative (eg Metalex).
- Plastic drain coil and filter sock – the length of the wall.
- Old sheets of hardboard, cardboard or plasterboard.
- Bracing timber, pegs and nails.
- Geotextile fabric.
Getting Started
1. Plan and Measure
Draw a plan and take measurements to calculate materials required for this project.
2. Creating Space for the Retaining Wall
You need at least a 250mm gap between the back of the wall and the face of the bank. Decide where you want the wall and cut back the face of the bank if necessary.
3. Level the Ground for Proper Drainage
Make sure that the ground behind the wall line is level, or slopes toward the end where you want it to drain.
4. Digging Holes for the Wall
Dig 500mm diameter holes every 1.2M along the line of the wall. The depth of the holes should be equivalent to 70% of the height of the wall. Examples: wall height 1M – hole depth 700mm, wall height 1.5M – hole depth 1.05M. If you have an engineer’s design, the hole depth will be specified.
5. Setting the Posts in Concrete
Put 100mm of concrete into the two end holes. Set posts on top of the concrete. Make sure only uncut post ends go into the holes. If that isn’t possible, paint cut ends with liberal amounts of timber preservative. Check that the top of the posts sit high enough.
6. Leaning Posts for Stability
Lean posts slightly back into the hill (for a dead vertical wall, set the posts even deeper into the ground).
7. Bracing and Aligning Posts
Brace posts. Check that you have exactly the same lean back on both posts and they are plumb (vertical) when viewed from the front (see below).
8. Filling and Tamping the Holes
Fill the holes with concrete to within 100mm of ground level. Then tamp the concrete down with a piece of 100 x 50 timber, brace and leave to set.
9. Aligning Intermediate Posts with String Lines
Run string lines top and bottom between the two set end posts. Use these as guides to line up intermediate posts. Set them in their holes the same way as the end posts.
10. Allow Concrete to Set
When all posts are in place, leave a couple of days for the concrete to set properly. The use of Dricon Rapid Set can speed this process up.
11. Attaching Horizontal Rails to the Posts
Nail horizontal rails (logs) to the back of the posts, starting at the bottom and working to the top of the wall. Join rails only on the posts. The gaps that occur between them will allow water to percolate through.
12. Installing Drainage System for the Wall
When the wall is complete, lay about 50mm of clean drainage metal along the bottom at the back of the wall. Cover drain coil (punctured) with a filter sock then lay on top of the metal and cover with about 250mm more drainage metal. If possible, protrude the drain coil at both ends so you can flush it with a garden hose from time to time.
13. Adding Drainage and Soil Behind the Wall
Position old sheets of hardboard, cardboard, or plasterboard down the back, about 250mm behind the wall. Keeping the level the same on both sides of the sheets, fill between them and the wall with more drainage metal; and behind with any dug out soil or clay. Take the metal to within 300mm of the ground surface at the top of the wall, place geotextile fabric over free draining gravel, and then fill with topsoil. The drainage metal is needed as far as possible up the back of the wall for optimum drainage. The sheets contain it, so you don’t use any more than necessary. They will eventually disintegrate (see below).
14. Wait for Concrete to Set Before Compacting Backfill
If your wall is to support new fill, leave at least two more weeks for the concrete to set completely before vigorously compacting the backfill.
| Timber Selection Guide | ||
| Treatment Level | Application | Typical Uses |
| H4 | For timber exposed to the weather and in-ground contact | • Fence posts • Pergola post • Retaining wall TGV and lumber |
| H5 | For timber exposed to the weather, ground and fresh water contact; and in high risk, loadbearing applications | • Piles (house foundations, retaining walls, and in decking piles) • Vineyard supports • Veranda posts • Poles |
| Note: |
|
Consumer Information and Handling Guide for Treated Timber is available at your local PlaceMakers store. |
Limitations of Liability: This article has been produced with proper care, however the advice offered within is general in nature. PlaceMakers is not responsible for the application of the advice offered and takes no responsibility for the accuracy or completeness of it. PlaceMakers will also not be liable for any consequential loss howsoever arising from the use of goods sold, nor for any loss caused by defective or inadequate structures in which goods are incorporated.
Explore the PlaceMakers Retaining Wall Range
Looking to transform your outdoor space into a level lawn, safe play area, or an attractive garden with raised beds and sheltered patios? Our selection of timber retaining walls can help you achieve your dream. By introducing changes in level, you can reimagine your garden in layers, maximize its natural height, and create shaded and private areas. Let us help you reclaim unloved spaces and revitalize your outdoor living.
Explore now:
Rough Sawn Retaining Timber
Our rough sawn retaining timber is a straight-grained sustainable wood with a classic even texture that will bring a strong natural finish to your garden design. This versatile treated timber is perfect for creating raised beds, supporting terraced lawns, and retaining difficult spaces. A durable material, your rough sawn timber wall will look at home in a range of spaces and will weather naturally in keeping with its surroundings.
- Rough sawn square edge
- Radiata Pine from sustainably grown NZ plantations
- Natural environmentally friendly material
- H4 treated (resists water and prevents rot)
- CCA pressure treated (resists fungi & insect damage)
- Suitable for ground contact applications
- Available in two sizes: 150x50mm & 200x50mm
Tongue & Groove Retaining Timber
A traditionally sturdy close-fitting design, tongue and groove offer lasting quality with a clean profile and a smooth-looking finish. Interlocking tongue and groove timbers are an ideal solution for various retaining walls, creating an attractive backdrop for an enclosed patio, sheltered play area or to support a terraced lawn. Consider turning a low tongue and groove wall into bench seating or top with one of our attractive trellis or decorative landscaping screens to create a private area perfect for entertaining.
- Tongue and groove profile
- Radiata Pine from sustainably grown NZ plantations
- Natural environmentally friendly material
- H4 treated (resists water and prevents rot)
- CCA pressure treated (resists fungi & insect damage)
- Suitable for ground contact applications
- Available in two sizes: 150x50mm & 200x50mm
SureWall Retaining Walls
SureWall is the new no-nonsense way to build quick and easy retaining walls with a flush finish and a striking contemporary look. Using a sliding-together system, the timber slots into place using heavy-duty steel posts, to create an attractive wall of robust construction that’s only 1/3 the thickness of conventional timber retaining walls. The SureWall system is the perfect solution for a wide variety of retaining walls including accessible raised vege patches, terraced lawn edging, and sunken garden designs with retained planted borders. Simply select the timber of your choice, and you’re good to go.
- Easy to install with minimum excavation required
- Flush contemporary finish
- Suitable for walls up to 1m
- High tensile galvanised steel joiner and end posts for long life
- No need for fasteners, saving time and money
- Suitable for ground contact applications
- Use your choice of 50mm timber
- Option to add a decorative SmartScreen in a selection of NZ-inspired designs
Popular Timber Retaining Wall Products
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