Yes, attaching a trellis to an existing Colorbond fence is generally a DIY-friendly job for most NZ homeowners. That said, there are a few important considerations around fixing methods, height limits, and your local council rules that are worth understanding before you grab the drill.
Check Your Fence Height and Council Rules First
This is the most important step. In New Zealand, fences (including any trellis attached to them) are subject to height limits under the Resource Management Act and your local council's district plan. Most councils allow boundary fences up to 2.0 m in height without a resource consent, but this varies — some allow up to 2.5 m in certain zones, while others are stricter near road boundaries.
If your existing Colorbond fence is already close to the maximum permitted height, adding a trellis on top could push it over the limit and require resource consent. Always check with your local council before you start. Building consent is generally not required for a simple trellis attachment, but confirm this with your council as well — requirements can differ depending on your region and the nature of the structure.
For general guidance on what requires building consent, MBIE Building Performance is a great starting point.
Understanding Your Colorbond Fence Structure
Colorbond is a steel sheet fencing system with vertical steel posts (typically set in concrete) and horizontal rails to which the steel panels are fixed. Before attaching anything, you need to understand what you're fixing into:
- Steel posts and rails — these are the structural elements and the best place to anchor a trellis
- Colorbond panels — the thin steel sheeting between rails; avoid fixing directly into these as it can cause the panels to flex, distort, or allow water ingress
Always aim to fix your trellis brackets to the posts or rails, not the panels themselves.
Choosing the Right Trellis and Fixings
For a Colorbond fence, you have a couple of good options:
Freestanding Trellis Panels Attached to Posts
This is the most structurally sound approach. Timber or powder-coated steel trellis panels can be bolted or bracketed directly to the existing steel posts using tek screws (self-drilling screws for steel) or through-bolts with appropriate washers.
Lightweight Trellis Fixed to Rails
A lighter timber or wire trellis can be attached to the horizontal rails using saddle brackets or U-bolts designed for steel sections. Keep the trellis lightweight if fixing to rails only.
Key tips for fixings:
- Use galvanised or stainless steel fixings to prevent rust staining on the Colorbond — this is especially important in coastal NZ environments
- Seal any drilled holes with a zinc-rich touch-up paint or a suitable sealant to prevent corrosion at the penetration point; Resene stocks suitable metal primers and touch-up products
- Avoid over-tightening fixings into the steel panels, as this can crack the paint coating
Consider the Wind Load
New Zealand can experience significant wind, and a trellis covered in climbing plants acts like a sail — it dramatically increases the wind load on your fence. This is particularly relevant in exposed areas or higher wind zones (check BRANZ for NZ wind zone information).
If you're planning a large or heavily planted trellis, consider:
- Whether your existing fence posts are robust enough to handle the extra load
- Adding intermediate posts for support if the span is long
- Choosing an open lattice design that allows wind to pass through rather than a solid panel
Protecting the Colorbond Coating
Colorbond's factory finish is durable, but it can be damaged by abrasion or incompatible materials resting against it. If you're attaching a timber trellis:
Boundary and Neighbour Considerations
If the fence sits on a shared boundary, it's good practice (and sometimes legally required) to discuss any modifications with your neighbour before starting work. The Fencing Act 1978 governs shared boundary fences in NZ, and making significant changes without agreement can cause disputes. A trellis that overhangs the neighbour's side is particularly worth discussing.
When to Call a Professional
While this is generally a DIY-friendly project, consider hiring a qualified fencer or builder if:
- Your fence is close to or at the maximum permitted height and you need advice on consent
- You want to add a large or heavy trellis structure that may require additional posts or structural assessment
- You're unsure about the condition of your existing fence posts (e.g., signs of rust or movement)
- The fence is on a steep or unstable site
A qualified fencer can assess your existing fence's structural capacity and recommend the best attachment method. You can find experienced local fencers on tradedirectory.co.nz.
Note: Attaching a trellis to a fence does not involve electrical, plumbing, or gas work, so there are no restricted trade licensing requirements for this task.
