Treated vs Untreated Timber – What’s the Difference?
When you're planning a job, one of the first things to figure out is whether you need treated or untreated timber. It’s not always obvious, especially if you’re new to building or doing a bit of DIY — but picking the right type of wood for the conditions will save you time, money, and hassle later on.
At Wood Green Timber, we stock a wide range of both treated and untreated timber, and we’ll always help you choose what’s best for your project.
What is Treated Timber?
Treated timber has been pressure-treated with preservatives to protect it from rot, insects, and moisture. It usually has a green or brown tint depending on the treatment type, and it’s designed for outdoor or exposed environments.
You’ll want treated timber for anything that lives outside or touches the ground.
Common uses for treated timber:
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Fence posts and rails
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Featheredge boards
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Sleepers
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Decking frames
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Garden builds
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Retaining walls and raised beds
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External joists (with correct treatment class)
We stock a wide range of green treated softwood — and some sizes are also available in brown on request.
What is Untreated Timber?
Untreated timber hasn’t gone through any preservative treatment — it’s clean, dry, and great for internal use or decorative jobs where exposure to moisture isn’t an issue.
It’s easier to paint, stain, or oil without any prep, and it’s often used in joinery and visible work.
Common uses for untreated timber:
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Stud walls and internal framing
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Shelving, trims, and boxing-in
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Furniture and cabinetry
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Planed sections for decorative finishes
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General indoor construction
Untreated timber should never be used outdoors unless you’re treating and sealing it yourself.
When Should You Use Which?
Here’s the general rule of thumb:
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Use treated timber anywhere outdoors, in contact with the ground, or exposed to damp and weather
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Use untreated timber for internal work, dry conditions, or decorative applications
Still not sure? Just ask — we’ll help you figure it out.
What We Stock at Wood Green Timber
We keep a full range of treated and untreated timber in stock at both our Wood Green and Potters Bar branches.
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Green treated softwood in multiple sizes and lengths
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Brown treated options available
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Untreated planed and sawn timber for interior work
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UC2 treated timber, often used for decking frames
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UC3 and UC4 joists available to order quickly if required
All of our timber is FSC® and PEFC™ certified and sourced from trusted Scandinavian mills.
Need Help Choosing?
Give us a call, drop us a message, or pop into the yard. Tell us what you’re building and we’ll tell you what you need — no fuss, no upsell, just proper advice from people who actually know timber.
Wood Green Timber — family-run, straight-talking, and here to help since 1981.
