Total Sheds
Buying Guides · 6 min read
Tanalised timber has preservative forced deep into its cells, not painted on. How it works, how long it lasts and what it means for your shed.
From the treatment yard
Every framing timber that leaves our West Midlands workshop is pressure-treated before we cut a single joint. Here's what that actually means — and why it's the difference between a shed that lasts decades and one that needs rescuing every summer.
Tanalised timber is wood that has had preservative forced deep into its cells under vacuum and pressure inside an industrial cylinder — not brushed, sprayed or dunked onto the surface. That one difference decides whether your shed shrugs off rot for decades or fights a losing battle from year one.
We've built garden buildings in our own workshop since 1995, and tanalised framing in FSC-certified timber is standard on every one — never an optional extra. This guide covers what matters when you're choosing a shed; if you want the full nuts and bolts of our own process, there's a detailed tanalising explainer too.
It's an industrial process, not a coat of paint. The timber goes into a sealed treatment cylinder and comes out changed all the way through.
Sawn timber is stacked and loaded into an industrial treatment cylinder — a giant sealed pressure vessel — and the door is locked down.
A powerful vacuum pulls the air out of the timber's cells, leaving millions of tiny empty pockets ready to take up preservative.
The cylinder floods with a copper-based preservative such as Tanalith, and hydraulic pressure drives it deep into those emptied cells — into the body of the wood, not just the outer millimetre.
Tip: The copper is what gives fresh tanalised timber its distinctive green tint.
A last vacuum draws off the excess, then the timber is left to dry while the preservative fixes permanently within the wood.
The finished timber is treated to Use Class 3 — certified for outdoor use above ground, which is precisely the job a shed frame does for the next few decades.
Careful: Sawing during assembly exposes untreated end grain. Brush every cut end with end-grain preservative as you build — a two-minute job that keeps the protection continuous.
Fresh from the cylinder, tanalised timber carries a green or brown tint. Over the first year or two it mellows to a warm honey, and left entirely alone it silvers to a soft grey. The colour changes; the protection doesn't. That weathering is the character of the wood, not a warning sign.
It also rewrites the maintenance rulebook. A dip-treated shed puts you on a treadmill: re-coat every year or watch the warranty and the timber fail together. Tanalised timber doesn't need an annual coat to resist rot — the protection is fixed in the cells, not sitting on the surface. Our written warranty does ask for an annual preservative coat (belt and braces — and it keeps the colour fresh), but that's a quick top-up on timber that's already protected through and through, not a rescue job. If you fancy a colour, stain or paint over it once the timber is fully dry. Our maintenance guide covers what's involved.
One honest caveat: treatment protects the timber that gets wet, but a dry building needs more than treated walls. That's why every build of ours pairs tanalised framing with a breathable membrane — the other half of keeping moisture out — and why we're such believers in EPDM rubber roofing up top. If you're weighing up frame options, our Standard vs Heavy Duty vs Composite comparison lays them side by side, or you can size one up directly in the Build Studio.
The copper-based preservative is fixed right through the timber, so the fungi behind wet rot find nothing hospitable — even where the surface gets scuffed.
Woodworm and other borers won't set up home in treated cells. The protection runs as deep as they'd ever tunnel.
The lower boards take splash-back off the base all winter — the classic first failure point on a cheap shed, and a non-event on a tanalised one.
Freeze, thaw, weeks of sideways drizzle: Use Class 3 treatment is specified for exactly this life, outdoors and above ground, year after year.
Tanalised timber does the hard work for you. A few build-day habits make sure nothing undoes it.
Not to stop rot — the preservative is fixed deep in the timber and does that job for decades without help. Two habits still matter: brush end-grain preservative onto any ends you cut during assembly, and give the building an annual preservative coat — our written warranty asks for it, and it keeps the colour fresh. Stain or paint is a separate, purely cosmetic choice.
Decades. Vacuum-pressure treatment to Use Class 3 protects against rot, fungal decay and insect attack for the long haul — it's the same treatment specified for fence posts and decking that live outside permanently. A dip-treated shed, by contrast, is only ever as good as its most recent coat.
That's the copper in the preservative showing through. The green (sometimes brown) tint is the sign the treatment went in, and it weathers naturally — to honey within a year or two, then a soft silver-grey over time. The colour change is cosmetic; the protection underneath doesn't fade with it.
Yes — once the timber is fully dry. The treatment protects the wood but doesn't dictate its colour, so any decent exterior stain or paint will take. Plenty of our customers leave theirs to silver naturally instead, and that's a perfectly good choice too.
Modern copper-based preservatives fix permanently into the timber as it dries, which is why the same treatment is used on decking, fence posts and garden play equipment across the UK. Two sensible habits: never burn treated offcuts, and if you're building raised veg beds against it, a simple liner is cheap peace of mind.
Every framing timber we build with is pressure-treated before it's cut, in the same family workshop that's been making sheds since 1995 — with free delivery across mainland UK. Browse the range, or design your own from scratch: the treatment's already included either way.
Browse tanalised shedsReady to put it into practice? Every building is made in our West Midlands workshop with free mainland delivery.
Browse buildings →