When it comes to timber in New Zealand, whether you’re building a deck, building a fence, landscaping your garden or framing a house, one key decision can make or break your project, what type of timber to use?
Let’s break down the differences, why they matter, and when you should choose one over the other.
What is Treated Timber?
Treated timber has been chemically treated to protect it against rot, insects (like borer or termites), and fungal decay. In New Zealand, where our climate can be harsh with wet winters, coastal air, and high humidity choosing the right timber treatment is especially important
There are different treatment levels, with H1.2 to H6 classifications used to define the hazard level the timber can withstand:
- H1.2: Indoor framing, protected from the weather but at risk of borer.
- H3.2: Outdoor timber above ground – like decks, fence palings, or pergolas.
- H4: In-ground contact – think fence posts, garden edging or retaining walls.
- H5/H6: High-risk areas – piles, poles, or marine use.
The most common treatment in NZ is CCA, but newer, eco-friendlier options are also on the rise, but at this stage, are a more expensive alternative.
What is Untreated Timber?
Untreated timber is exactly that natural wood with no added preservatives or chemicals. It’s commonly used for indoor furniture, wall linings, animal pens and interior framing on sheds where there’s minimal risk of moisture or pest damage.
New Zealand grown pine or oregon are often used untreated for aesthetic or environmental reasons, especially in projects where chemical-free timber is preferred, like kids’ toys, cabinetry, heritage restoration or post and rail fencing around animals.
When to Use Treated Timber
Outdoor builds (decks, fences, landscaping):
Go treated. It’s built to last.
Wet or humid zones (bathroom frames, basements): Treated is safer.
Ground or water contact:
Always treated; Untreated wood will rot fast.
When to Use Untreated Timber
Indoor furniture or decorative timber:
Keeps the natural look and feel.
Projects needing low-toxicity materials:
Ideal for eco-conscious builds or animal fencing.
Shed framing:
Can be an option in a controlled environment.
So, Which One’s Better?
It depends on your project. Treated timber will last longer outside and will require less maintenance. Untreated timber is cleaner and more natural but won’t’ last as long.
The key is choosing the right grade for the job and don’t cut corners. We understand you want to keep costs down using untreated timber outside, but in NZ’s conditions, that may mean a bigger bill down the line.
Need Help Deciding?
At Canterbury Timber and Hardware, we have both treated and untreated timber options ready to go, and the knowledge to make sure we provide the right products for your project. Whether you’re after durability, aesthetics, or both, we will help you find the right timber. Drop in for a chat or give us a call, we’re always happy to help.