You don't need expensive surveying equipment to set out a straight retaining wall — with a few basic tools and a bit of patience, you can achieve accurate, professional results. The key is using batter boards, a string line, and the classic 3-4-5 triangle method to establish straight lines and true right angles before you dig a single spade of soil.
What You'll Need
Gather these tools before you start:
- Timber stakes (at least 600 mm long) and a mallet
- Batter boards (short horizontal timber pieces nailed to stakes)
- Builder's string line (bright nylon, not stretchy)
- A long tape measure (at least 10 m)
- A line level or water level
- A permanent marker
- A plumb bob or spirit level
- Spray paint or sand for marking the ground
Step 1 – Establish Your Reference Points
Start by identifying the start and end points of your retaining wall. These might be fixed by a boundary, a driveway edge, or an existing structure. Mark both points with a timber stake driven firmly into the ground.
If your wall needs to run parallel to a boundary or building, measure equal distances from that reference at both ends and mark accordingly. This gives you two anchor points to work from.
Step 2 – Set Up Batter Boards
Batter boards are the tradesperson's secret weapon for accurate layout. Drive pairs of stakes about 600–900 mm beyond each end of your wall line (so they won't be disturbed when you excavate). Nail a horizontal timber crosspiece to each pair of stakes at a consistent height — ideally just above finished ground level.
Stretch your string line between the batter boards, directly over your two anchor points, and tie it off. Use a plumb bob to confirm the string sits exactly over each stake. This string now represents the face of your retaining wall.
Step 3 – Check for Straightness
Once your string is tensioned, sight along it from one end with your eye close to the line. Any bow or sag will be obvious. Adjust the string tension or the batter board position until the line looks perfectly straight.
For longer walls (over 6–8 m), add an intermediate batter board in the middle to prevent the string from sagging under its own weight.
Step 4 – Square Up Corners Using the 3-4-5 Method
If your wall has a corner or needs to run at a right angle to another structure, use the 3-4-5 triangle method (based on Pythagoras' theorem):
- From the corner point, measure 3 m along one string line and mark it.
- Measure 4 m along the other string line and mark it.
- The diagonal distance between those two marks should be exactly 5 m if the corner is a true 90°.
- Adjust one string line until the diagonal measures exactly 5 m.
For greater accuracy on longer walls, scale up: use 6-8-10 m or 9-12-15 m multiples.
Step 5 – Mark the Ground
Once your string lines are set and squared, use spray paint or a sand line directly below the string to mark the wall line on the ground. This gives you a clear guide for excavation that won't disappear when you remove the string.
Mark both the face line and the back of footing line (accounting for your wall thickness and any required footing width).
Step 6 – Check Levels
Use a line level (a small spirit level that clips onto your string) or a water level (a length of clear hose filled with water) to check that your string line is level along its length, or to establish a consistent fall if your wall steps down a slope.
Note the height difference between each end — this will determine how many courses your wall needs and whether you'll need to step the footing.
NZ Building Code Considerations
Before you start building, check whether your retaining wall requires a building consent. Under the NZ Building Code and Schedule 1 exemptions, retaining walls up to 1.5 m in height (with no surcharge loading such as a driveway or building nearby) are generally exempt from consent — but always confirm this with your local council, as conditions vary.
Walls over 1.5 m, or any wall retaining a driveway or structure, will almost certainly need consent and may need to be designed by a structural engineer. BRANZ has useful guidance on retaining wall construction standards and best practice.
If your wall is near a boundary, check with your council about setback requirements and whether a Licensed Building Practitioner (LBP) is required for the work. You can verify LBP credentials at lbp.govt.nz.
When to Call a Professional
Setting out is something many confident DIYers can handle, but the actual construction of a retaining wall — especially anything over 1 m high — involves significant structural and drainage considerations. Consider hiring a qualified retaining wall builder if:
- Your wall will be over 1 m high
- There is a building, driveway, or heavy load above the wall
- The ground is unstable, waterlogged, or on a steep slope
- You're unsure about drainage, footing depth, or tie-back requirements
- A building consent is required
A professional will also ensure your wall meets NZ Building Code requirements and won't create liability issues down the track. You can find qualified local retaining wall builders on tradedirectory.co.nz.