A tension wire along the bottom of a fence is one of the most effective ways to keep netting pulled tight, stop animals burrowing underneath, and give your fence a neat, professional finish. The job is well within reach of a capable DIYer — you'll need the right wire, a few basic tools, and a bit of patience to get the tension even.
What You'll Need
Before you start, gather your materials and tools:
- High-tensile or mild steel wire — 2.5 mm or 3.15 mm diameter is typical for bottom wires on farm and lifestyle-block fences. High-tensile wire holds tension better over long runs but requires more care when straining.
- Wire strainer (fencing strainer) — a ratchet or lever-action strainer. Never over-tension; high-tensile wire can snap back dangerously.
- Wire staples or clips — to fix the wire to timber posts, or wire ties/clips for steel waratahs or steel posts.
- Straining posts (end assemblies) — your end and corner posts must be robust enough to take the load. Undersized end posts are the most common cause of a sagging bottom wire.
- Pliers and wire cutters — fencing pliers are ideal as they cut, grip, and staple.
- Gloves and safety glasses — wire under tension is a serious hazard.
- Measuring tape and a line level or string line — to keep the wire at a consistent height.
Choosing the Right Wire
| Wire Type | Best Use | Notes |
|---|---|---|
| High-tensile (HT) 2.5 mm | Long runs, farm fencing | Springy — needs care straining |
| Mild steel 3.15 mm | Shorter runs, garden fencing | Easier to work with |
| Galvanised wire | Most outdoor NZ conditions | Standard choice for longevity |
| Stainless steel | Coastal/high-corrosion areas | More expensive but longer-lasting |
For most NZ lifestyle blocks and rural properties, galvanised high-tensile wire is the go-to choice. In coastal areas where salt air accelerates corrosion, consider a heavier galvanising coating or stainless steel.
Step-by-Step Installation
1. Check Your End and Corner Posts
The tension wire pulls hard on your end assemblies. Make sure your straining posts are set at least 900 mm into the ground (deeper in soft soils), back-braced or box-braced, and solid before you start. A wobbly end post will let the wire sag within weeks.
2. Set Your Wire Height
Decide how high off the ground your bottom wire will run. For keeping rabbits out, 50–100 mm is common. For sheep or cattle netting, the wire often sits right at ground level or just above. Use a string line between your end posts to mark a consistent height along the run.
3. Attach the Wire at One End
At your first straining post, create a secure end loop using a figure-eight knot or a crimped wire ferrule. Wrap the wire around the post or through the eye of a straining bolt, then twist or crimp it back on itself at least three times. This anchor point must not slip.
4. Run the Wire Along the Fence Line
Unroll the wire along the fence line, keeping it on the ground or resting loosely against the posts. Don't try to tension it as you go — just get it in position first. Keep the roll controlled; a spinning wire reel can cause tangles and injury.
5. Attach to Intermediate Posts
At each intermediate (line) post, fix the wire loosely with a staple (for timber posts) or a wire clip/tie (for steel posts or waratahs). Drive staples at a slight angle and leave them slightly proud — not hammered flush — so the wire can slide a little during tensioning. You'll tighten them fully after straining.
6. Strain the Wire
At the far end post, attach your wire strainer between the wire and a secure anchor point. Slowly apply tension using the ratchet or lever action. Watch the wire along the full run — you want it to lift off the ground slightly and sit at your target height with a gentle, even tension.
Do not over-tension. High-tensile wire that is over-strained can snap suddenly and cause serious injury. A good rule of thumb: the wire should have very slight give when you press it firmly with your thumb mid-span — it shouldn't be guitar-string tight.
7. Secure the End and Fix Intermediate Staples
Once you're happy with the tension, secure the wire at the end post using the same figure-eight or crimp method as the start. Then go back along the line and drive your intermediate staples home (or tighten your clips), keeping the wire at the correct height at each post.
8. Attach Netting to the Tension Wire
If you're running netting above the tension wire, tie or clip the bottom of the netting to the wire at regular intervals (every 150–300 mm is typical). This keeps the netting from lifting and animals from pushing underneath.
Safety First
Wire under tension stores a lot of energy. Always wear gloves and safety glasses when straining wire. Keep bystanders — especially children — well clear of the wire run while tensioning. Never stand directly in line with a wire being strained. If a wire snaps or a staple pulls out, the recoil can cause serious cuts or eye injuries. WorkSafe NZ has guidance on safe manual handling and working with tools if you'd like to brush up on best practice.
Common Mistakes to Avoid
- Weak end posts — the single biggest cause of failure.
- Over-tensioning — especially with high-tensile wire.
- Stapling too tight at intermediate posts — the wire needs to move slightly during tensioning.
- Ignoring ground contours — on uneven ground, you may need to adjust the wire height post by post rather than running it dead straight.
When to Call a Professional
Fencing is not restricted work under NZ law, so there are no licensing requirements for a standard fence. However, if your project involves electric fencing near overhead power lines, contact your lines company before starting — WorkSafe NZ sets minimum safe distances. If your fence is on or near a property boundary, check with your local council about any consent requirements or boundary rules. For large-scale rural fencing, steep terrain, or if you're simply not confident, a qualified fencer will get the job done efficiently. You can find experienced local fencers on tradedirectory.co.nz.
