Keeping fence posts level on uneven ground is one of the most common challenges for DIY fencers in New Zealand, where hilly sections and undulating terrain are the norm rather than the exception. The good news is that with the right technique, the correct tools, and a bit of patience, you can achieve a sturdy, good-looking fence even on a significant slope.
Understand Your Options First: Stepped vs Raked Fencing
Before you dig a single hole, decide which fencing style suits your site.
- Stepped (or stair-step) fencing – The rails and panels drop in flat, horizontal sections, creating a staircase effect. This works well with pre-made panels and on steeper slopes.
- Raked (or parallel) fencing – The rails run at an angle that follows the slope, so the fence flows continuously with the ground. This suits timber paling and post-and-rail styles and looks more natural on gradual slopes.
- Contour fencing – Used on very uneven or undulating ground where neither a clean step nor a straight rake is practical. Each bay is individually adjusted.
Choosing the right style upfront will determine how you set out your posts and measure your heights.
Tools You'll Need
- Spirit level (at least 1.2 m long) or a digital level/level app for checking plumb
- String line and line level (or a laser level) for establishing a consistent height datum
- Tape measure
- Batter boards or temporary stakes to hold your string line
- Post hole borer (manual or petrol-powered — hire from Bunnings or Mitre 10)
- Concrete (rapid-set bagged mix is convenient for most DIY jobs)
- Temporary braces (timber offcuts and stakes to hold posts while concrete sets)
Step 1: Set Up a String Line as Your Datum
A string line is your best friend on uneven ground. Drive a stake at each end of the fence run and stretch a taut string line between them at a consistent height above ground — say, 300 mm above the highest point of the ground along the run. Use a line level or laser level to confirm the string is truly horizontal.
This gives you a fixed reference point from which to measure down to the ground at each post position, so you know exactly how deep each hole needs to be and how tall each post needs to be above ground.
Step 2: Mark and Dig Your Post Holes
Mark post positions along the string line at your chosen spacing (typically 1.8–2.4 m for most residential timber fences). Because the ground height varies, each hole will be a different depth — but your goal is to have all post tops at the same height relative to your string line datum, or stepping down at consistent intervals for a stepped fence.
As a general rule, posts should be buried to at least one-third of their total length in the ground, with a minimum of 600 mm depth for most residential fences. On soft or sandy soils, go deeper. Check with BRANZ guidance or your local council if you're unsure about soil conditions in your area.
Step 3: Set Posts Plumb — Not Vertical to the Slope
This is where many DIYers go wrong. Posts must be plumb (truly vertical) regardless of the slope — they should not lean to follow the angle of the ground. Use your spirit level on two adjacent faces of each post to confirm it's plumb in both directions.
Hold the post in position with temporary timber braces nailed to stakes in the ground. Check plumb again before and after pouring concrete, as posts can shift slightly.
Concrete Tips
- Use a rapid-set concrete mix (available from PlaceMakers or hardware stores) for convenience.
- Flare the concrete slightly above ground level and slope it away from the post to shed water — this helps prevent rot at the base.
- Allow concrete to cure fully (check the bag for times) before attaching rails.
Step 4: Cut Posts to a Consistent Height
Once all posts are set and the concrete has cured, use your string line again to mark a cut line across all posts at the desired finished height. A chalk line snapped across the posts works well. Cut each post to this line with a circular saw or handsaw. This is what gives your fence that clean, level top rail line — even though the ground beneath is anything but flat.
For a stepped fence, mark each section's height separately, dropping by a set amount (e.g., 150 mm or 300 mm) per step.
Step 5: Attach Rails and Infill
With posts set plumb and cut to height, attach your top and bottom rails using appropriate brackets or by notching into the posts. On a raked fence, cut the rail ends at the slope angle so they sit flush against the post face. Pre-drill to avoid splitting timber.
For paling fences, hang a string line between posts at the desired paling height to keep each paling consistent as you nail or screw them on.
When to Call a Professional
Some situations are best left to a qualified fencer:
- Retaining walls combined with fencing — if your fence needs to retain soil, this may require a building consent and engineering input. Check with your local council, as requirements vary. The MBIE Building Performance website has useful guidance on when consents are needed.
- Boundary fences — disputes or shared costs with neighbours are governed by the Fencing Act 1978; a professional can help navigate this.
- Very steep or unstable ground — post spacing, depth, and bracing requirements may exceed standard practice.
- Large or complex projects where getting it wrong means expensive remediation.
You can find experienced, local fencing contractors on tradedirectory.co.nz to get quotes and advice specific to your site.
