Adding a trellis panel to an existing fence is a satisfying weekend project that can boost privacy, support climbing plants, and add visual interest to your outdoor space. With the right materials and a bit of planning, most NZ homeowners can tackle this job themselves — no specialist licence required.
Plan Before You Build
Before picking up a saw, take a few measurements and think through your design:
- Measure the opening or bay where the trellis will sit — width between posts and the height you want the trellis to reach above the existing fence line.
- Check your fence height. In most NZ residential zones, a fence (including any trellis on top) over 2.0 m on a boundary may require a building consent. Rules vary by council, so always confirm with your local council before you build. Some situations fall under Schedule 1 exemptions of the NZ Building Code, but don't assume — check first.
- Consider the wind. New Zealand can be very windy, especially in Wellington, Canterbury, and coastal areas. A solid trellis acts like a sail, so an open lattice design is generally safer and puts less stress on your existing fence posts.
Tools and Materials You'll Need
Tools:
- Tape measure, pencil, and square
- Circular saw or hand saw
- Drill/driver and drill bits
- Level
- Safety glasses and hearing protection
Materials:
- Treated timber battens (H3.2 treated for above-ground outdoor use is standard in NZ)
- Pre-made lattice or trellis panel (available at Bunnings or Mitre 10)
- Galvanised or stainless steel screws and joist hangers or timber cleats
- Exterior wood primer and paint or stain (check out options from Resene or Dulux)
- Post-cap or capping timber if extending post height
Always use H3.2 treated timber for any framing that will be exposed to the weather but not in ground contact. If a post needs to go into the ground, use H5 treated timber.
Step-by-Step: Building the Trellis Panel
1. Prepare the Frame Timber
Cut your frame pieces to size — you'll need a top rail, a bottom rail, and two vertical side pieces (stiles). A simple butt-jointed frame screwed together works well for most trellis panels. Pre-drill to avoid splitting.
2. Attach the Lattice or Trellis to the Frame
Lay the lattice panel flat on the ground and position your frame around it. Screw or staple the lattice to the inside face of the frame, keeping it square with a builder's square. Check the diagonal measurements are equal — if they match, the frame is square.
3. Fix the Frame to the Existing Fence
This is the most important structural step:
- If fitting between existing posts: Use galvanised timber cleats (small blocks of treated timber) screwed to the inside face of each post to create a ledge. Drop the trellis frame onto the cleats and screw through the frame into the posts.
- If sitting on top of the fence: You may need to extend the existing posts upward using a post extender or by bolting a new length of timber alongside the existing post. Ensure the join is solid — a wobbly post will mean a wobbly trellis.
- Use a level to check the frame is plumb and level before fully tightening all fixings.
- Use galvanised or stainless steel fixings throughout to prevent rust staining and corrosion in our damp NZ climate.
4. Finish and Paint
Apply a quality exterior primer followed by a paint or stain that matches or complements your existing fence. Resene and Wattyl both offer durable exterior timber coatings well suited to NZ conditions. Painting before installation makes it easier to coat all surfaces, but touch up any cut ends after fixing.
Height, Consent, and Boundary Rules
As a general guide, fences and attached structures (including trellis) over 2.0 m on or near a boundary are likely to need a building consent in most NZ councils. Some councils have specific rules about trellis being "open" (e.g. at least 50% open to the air) to qualify for an exemption. Always check with your local council before building — rules differ between territorial authorities. You can also find general guidance at MBIE Building Performance.
If the fence is on a shared boundary, talk to your neighbour before making changes — this is both good practice and may be a legal requirement under the Fencing Act 1978.
When to Call a Professional
This is generally a DIY-friendly project, but consider hiring a qualified fencer or builder if:
- Your existing fence posts are rotten, leaning, or undersized — adding a trellis will make the problem worse.
- The total fence height will exceed 2.0 m and you need help navigating consent requirements.
- You're working on a retaining wall fence combination, which has its own structural and consent considerations.
- The site is very exposed and you need engineering advice on wind loads.
A qualified local fencer can assess your existing fence and ensure the trellis is structurally sound. You can find experienced fencing professionals in your area on tradedirectory.co.nz.
