Yes, cladding existing deck posts with timber is a popular and achievable DIY project that can dramatically improve the look of an older or plain deck. With the right materials, preparation, and technique, you can transform rough-sawn or steel posts into something that looks polished and intentional — without replacing the structural posts themselves.
Understanding What You're Working With
Before you start, it's important to distinguish between the structural post (which carries the load of your deck) and the decorative cladding you're adding around it. The cladding is non-structural — it's purely cosmetic. This means you're not altering the load-bearing elements of the deck, which is good news from a building consent perspective.
However, you should still check with your local council before starting. Most cosmetic cladding work on existing decks falls under Schedule 1 exemptions of the Building Act 2004, meaning no consent is required — but this depends on your specific situation. Always confirm with your council rather than assuming.
Choosing the Right Timber
Because deck posts are exposed to the weather, moisture resistance is your top priority. Poor timber choice is the most common reason cladding fails prematurely.
Good options include:
- Treated pine (H3.2 or H4 rated) — widely available and cost-effective for above-ground exterior use
- Kwila (Merbau) — a dense, attractive hardwood popular for decking and trim
- Vitex — another durable hardwood option
- Cedar — naturally resistant to rot and lightweight, though pricier
Avoid untreated or H1/H2 timber outdoors — it won't last. Check with your local Mitre 10, Bunnings, or PlaceMakers for treated timber options suited to exterior use in your region.
How to Clad a Deck Post: Step by Step
1. Inspect the Existing Post
Before cladding anything, check the existing post for rot, damage, or movement. If the post is structurally compromised, cladding over it is not the answer — it needs to be repaired or replaced by a qualified deck builder first.
2. Plan Your Box Profile
The most common approach is to build a four-sided timber box around the post. Measure the post carefully and plan your cladding boards so the finished box looks square and proportional. A typical 100×100mm post might be clad to create a finished 150×150mm or 200×200mm profile.
3. Allow for Drainage and Ventilation
This is critical in New Zealand's varied climate. Trapping moisture between the cladding and the post will cause rot — sometimes in just a few seasons. Leave a small gap at the base of the cladding (don't run it tight to the deck surface), and consider small ventilation gaps or weep holes at the bottom to allow any moisture to escape.
BRANZ provides excellent guidance on moisture management in exterior timber assemblies — worth a read before you start.
4. Fix the Cladding Boards
Use stainless steel or hot-dipped galvanised screws or nails — never plain steel, which will rust and stain the timber. Fix boards securely but allow for slight timber movement. Secret-fixing systems give a cleaner look if you want to avoid visible fasteners.
5. Seal All End Grain
End grain absorbs moisture rapidly. Seal all cut ends with an appropriate timber end-grain sealer before installation, and again after cutting on site.
6. Finish and Paint or Oil
Once installed, finish the timber to protect it from UV and moisture. Options include:
- Exterior paint — Resene and Dulux both offer quality exterior timber paints
- Decking oil or stain — suits hardwoods like Kwila and gives a natural look
- Clear exterior varnish — shows off the timber grain but requires more maintenance
Always use a product rated for exterior timber use and follow the manufacturer's preparation and application instructions.
Moisture and the NZ Building Code
New Zealand's Building Code clause E2 (External Moisture) requires that building elements resist moisture ingress. While a deck post cladding isn't technically a wall, the same principles apply — poorly detailed cladding can trap water and cause hidden rot that's expensive to fix.
For guidance on exterior moisture management, MBIE Building Performance has useful resources on cladding and weathertightness.
Cladding Over Steel Posts
If your existing posts are steel (RHS or CHS), the same box-cladding approach works well. Make sure the steel is treated or painted to prevent rust before you enclose it, and again, allow for drainage and ventilation inside the box.
A Quick Comparison of Timber Options
| Timber | Durability | Cost (guide) | Appearance |
|---|---|---|---|
| Treated pine (H3.2) | Good | $ | Plain, paintable |
| Cedar | Very good | $$$ | Warm, natural grain |
| Kwila | Excellent | $$ | Rich, dark hardwood |
| Vitex | Excellent | $$ | Light hardwood |
Costs are approximate and vary by supplier and region.
When to Call a Professional
Cladding deck posts is well within DIY reach for a competent homeowner, but consider calling a qualified deck builder if:
- The existing posts show signs of rot, movement, or structural damage
- Your deck is elevated (over 1.5m) and you're unsure about working safely at height — check WorkSafe NZ guidelines for working at height
- You want a complex profile, routed detail, or built-in lighting that requires more advanced joinery skills
- You're unsure whether your project needs a building consent
A skilled deck builder can also ensure the finished result looks truly professional. You can find qualified local deck builders on tradedirectory.co.nz.
Licensed Building Practitioner (LBP)
