Choosing your greenhouse frame timber
The timber frame is the decision that outlasts everything else
Whichever timber you choose will been the main factor for the cost, durability and sustainabiliy impact of your greenhouse. This guide sets the three timbers options we offer side by side on what matters for the long haul: how long they last, how they're grown and sourced, and how you will need to maintain the timber once installed.
- Durable · Aromatic
Western Red Cedar
Imported from British Columbia, Canada
Our core timber, using 100% grade 2 clear and better cedar. This timber has few knots and very little defect. Cedar naturally resists rot, ages to a soft silver. The cedar is low maintenance and needs a preservative stain applying every 3-4 years.
- Local · Honest grain
British Cedar (Sterling)
Grown and milled in the UK
The same species grown closer to home. Paler and knottier, with the shortest journey of the three.The best sustainable choice
- Engineered · Longest guarantee
Accoya
Acetylated radiata pine
Fast-grown pine modified for exceptional stability. No maintenance required at all. The highest durability class available, and also the best base for a painted finish.
Find your matchFull comparisonUpgrading to AccoyaSustainability by timberSustainability explainedTalk to us
What matters most to you?
Move the sliders to weight your priorities. The match scores update as you go.
Your match right now
Indicative only, based on published manufacturer and industry data. Talk to us to confirm the right timber for your build or if you have further questions.
The full comparison
The same three timbers, attribute by attribute.
| Attribute | Western Red Cedar | British Cedar (Sterling) | Accoya |
|---|---|---|---|
| Expected lifespan | 30+ yearsNaturally durable heartwood | 20+ yearsFaster-grown UK cedar is rated moderately durable, one class below imported stock | 50 years above ground25 years in ground contact; Class 1, the highest durability rating |
| Guarantees | 10-year Woodpecker guaranteeStructural and against rot, standard across our range | 10-year Woodpecker guaranteeStructural and against rot, standard across our range | 50-year rot guaranteeFrom Accsys, the manufacturer, for above-ground use (25 years in ground). Plus our 10-year structural guarantee and a 10-year warranty on painted finishes |
| Maintenance | Very lowNatural oils protect it; leave to weather and stain with preservative every 3-4 years | Very lowWeathers evenly to silver | Very lowExceptional stability keeps doors moving freely and paint intact for longer |
| Sourcing & certification | British Columbia, CanadaPEFC Chain of Custody: we were the first in our industry to hold it, in 2013 | UK-grown and milledShortest supply chain; supports British forestry and jobs | FSC-certified radiata pinePlantation-grown on a roughly 30-year rotation; Cradle to Cradle Gold certified |
| Transport carbon | Long sea journeyAround 16,000 km by ship via the Panama Canal. Sea freight is efficient per tonne, so this adds only a small fraction of the carbon the timber stores | LowestA short road journey from UK forest to sawmill and workshop | Longest journeyNew Zealand pine is shipped around 20,000 km to the Netherlands for acetylation, then on to the UK |
| Deforestation risk at source | Low (EUDR)Canada is classed low risk by the EU. Old-growth logging in coastal BC remains contentious, which is why Chain of Custody paperwork matters | Low (EUDR)UK plantations managed under the UK Forestry Standard, with no old-growth question | Low (EUDR)New Zealand plantations, largely planted on former pasture rather than cleared native forest |
| Appearance & weathering | Rich red-brown, ages to silverNatural oils can leach and streak in the first months | Paler, more visible knotsMore consistent colour, weathers evenly | Pale, takes paint wellOur painted greenhouses are made from Accoya for this reason |
| Where it's weaker | ImportedA long journey from forest to garden | Less durable than imported cedarRated one durability class below imported stock, though still used for the whole frame of our Sterling greenhouses | Highest upfront costA premium timber |
| Relative cost | Mid | Lowest | Highest |
Thinking of upgrading to Accoya?
Western Red Cedar is our standard timber, and Accoya is available as an upgrade on any of our greenhouses. Here is how the two compare head to head.
| Criteria | Western Red Cedar (standard) | Accoya (upgrade) |
|---|---|---|
| Guarantee against rot | 10-year Woodpecker guaranteeNaturally durable heartwood (Durability Class 2) | 50-year manufacturer's guaranteeFrom Accsys for above-ground use (25 years in ground or fresh water); Durability Class 1 |
| Dimensional stability | GoodSome seasonal swelling and shrinkage, typical of natural timber | ExcellentAcetylation reduces moisture uptake by around 80%, minimising swelling, shrinkage and warping |
| Weathering and appearance | Silvers naturallyNatural oils give some early resistance to surface mould and algae while it weathers | Silvers naturallyMore prone to cosmetic surface mould in the first months; see the note below |
| Sustainability | PEFC-certified heartwood cedar | FSC-certified radiata pineCradle to Cradle Gold certified, non-toxic modification process |
| Strength and machining | Lighter and softerTraditional to work and finish | Denser and strongerMachines cleanly and holds paint and stain for longer |
| Best suited to | Most gardensGood all-round performance | Exposed, humid or coastal sitesWhere its extra rot resistance and stability count most, and for painted finishes |
| Cost | Included as standard | Upgrade at extra costAsk us for a quote for your greenhouse |
Worth knowing: early surface mould on Accoya
The acetylation process removes many of the natural sugars and extractives that give timbers like cedar some early resistance to fungal growth. As a result, Accoya can be more prone than cedar to superficial mould, algae or dark surface staining in the first few months after installation, especially in humid, shaded or poorly ventilated spots.
This is cosmetic and surface-level only. It does not affect the strength of the frame, the 50-year rot guarantee or the working life of the timber, and it usually fades as the wood weathers or once it is cleaned or coated. Clean affected areas with a gentle, non-alkaline wash: no alkaline cleaners and no pressure-washing. If you choose Accoya, we recommend a light clean of the frame during the first 12 months, paying particular attention to permanently shaded sides.
Sustainability, timber by timber
There is no single "greenest" timber. Each of the three wins on something different, so here is how they compare on the questions that matter most for the planet.
| Question | Western Red Cedar | British Cedar (Sterling) | Accoya |
|---|---|---|---|
| Emissions to produce | LowAbout 117 kg CO2e per m³ from forest to sawmill gate, most of it from harvesting and forest management | LowestSawn and dried in the UK with no modification. No published figure yet, but no long shipping or chemical process | HighestAround 1,000 to 1,100 kg CO2e per m³, mainly from making the acetic anhydride and running the modification plant |
| Carbon stored in the wood | About 620 kg CO2 per m³Locked away for the life of the greenhouse | Similar to imported cedarSame species and a similar density | About 816 kg CO2 per m³A denser timber, so it holds more carbon |
| Chemicals and treatments | NoneProtected by its own natural oils | NoneUntreated natural timber | Modified, not treatedAcetylated with acetic anhydride, a stronger form of the acid in vinegar. Nothing toxic is left in the wood, and process chemicals are recovered and reused |
| Timber miles | LongShipped around 16,000 km from Canada | ShortestUK forest to UK workshop | LongestNew Zealand to the Netherlands, then to the UK |
| Lifespan and replacements | 30+ yearsA long life from a low-energy timber | Shorter than imported cedarRated moderately durable, one class below imported stock | 50 years above groundFewer repairs, repaints and replacements, which spreads its production carbon over more years |
| Forests and wildlife | Managed natural forestReplanted after harvest but slow to regrow; old-growth logging in BC is contentious, so certified supply matters | UK plantationsManaged under the UK Forestry Standard, supporting British forestry and rural jobs | Fast-grown plantationsSingle-species pine, largely planted on former farmland rather than cleared native forest |
| End of life | BiodegradableCan be composted or burned for energy | BiodegradableCan be composted or burned for energy | RecyclableCradle to Cradle Gold certified; can be disposed of like ordinary wood |
| Its strongest green case | Proven and low-energyA natural, durable timber from a certified, traceable supply chain | LocalThe fewest timber miles and no processing beyond sawing and drying | Built to lastThe longest life and lowest upkeep over the decades |
Which is the greenest choice for you?
Lowest carbon to make
Choose British cedar or Western Red Cedar. Neither needs a chemical process, so far less energy goes into producing them.
Buying local
Choose British cedar. It has the shortest journey and supports UK forestry and sawmills.
Longest life, least upkeep
Choose Accoya. It lasts longest, holds paint best and needs the fewest repairs and replacements over its life.
Emissions figures are cradle-to-gate (forest to factory gate) from published Environmental Product Declarations: the Western Red Cedar Lumber Association (2025) and Accsys/Accoya (2026). They exclude shipping to the UK, and figures vary by plant and product, so treat them as indicative.
Considerations for Sustainability
Four questions worth asking of any "sustainable timber" claim, including ours: what it does to the carbon budget, who checked, what happens at the end, and where it actually grew.
Wood stores carbon rather than spending it to be made. As a tree grows it draws CO2 from the air and locks much of it into its structure: roughly 0.9 tonnes of CO2 per cubic metre of timber, depending on species and density. That carbon stays put until the wood eventually decays or burns, decades or centuries later.
Cladding, per square metre
Making aluminium cladding takes roughly 20 times the energy of milling the timber equivalent. Timber starts in credit: the carbon it stored while growing outweighs what it took to mill it. Recycling closes some of the gap for aluminium, but one lifecycle study puts it at up to 30 reuse cycles before recycled aluminium catches up with building in timber first time.
Growth speed cuts both ways. The radiata pine behind Accoya is harvested at around 29 years and replanted straight away, so it keeps absorbing carbon on a short, repeating cycle, though a young tree never banks as much as an old one. Western Red Cedar grows more slowly, so each board carries more stored carbon, but the forest regrows more slowly behind it. Transport adds to all three, which is why the comparison table includes timber miles.
Two different things get checked
Forest management certification is checked at the forest, verifying it's harvested, replanted and managed responsibly. Chain of Custody certification is a separate, ongoing check that follows certified timber through every hand it passes through, from forest to sawmill to workshop, with paperwork proving it was never mixed with uncertified stock. We have held PEFC Chain of Custody since 2013, the first in our industry to do so.
FSC or PEFC: does it matter which?
Both certify responsibly managed forests, and both are treated as equivalent by BREEAM, LEED and SKA. FSC applies one global standard; PEFC endorses national standards against a shared benchmark. What matters most is that a supplier holds a current Chain of Custody certificate. Accoya's pine is FSC-certified; our cedar supply chain runs on PEFC.
The EU Deforestation Regulation (EUDR)
From 30 December 2026, larger companies placing timber on the EU market must provide a due diligence statement, backed by the GPS location of the harvest site, proving the wood wasn't cut from land deforested after December 2020. The EU confirmed in May 2026 that there would be no further delay. Canada, New Zealand and the UK are all classed as low risk, which allows simplified due diligence, but the paperwork still has to be in place. It's an EU rule rather than a UK one, but it already shapes how we document sourcing for greenhouses heading to Europe.
What happens when it's eventually replaced
Cedar, Canadian or British, is untreated, unmodified wood. It biodegrades naturally or can be burned as fuel, with nothing added that needs careful disposal. Accoya is modified rather than treated: nothing toxic is added during acetylation, so its makers say it can be disposed of in the same way as ordinary wood, and it is Cradle to Cradle Gold certified.
Where the wood actually comes from
Western Red Cedar grows mainly on Vancouver Island and coastal British Columbia. Old-growth logging there is a genuine, ongoing point of contention, with only around a fifth of the original productive old-growth forest thought to remain. This is exactly what Chain of Custody exists to police: paperwork that proves timber came from a managed, replanted forest.
British cedar comes from UK plantations managed under the UK Forestry Standard, with the shortest supply chain of the three and no old-growth question.
Accoya's radiata pine grows on New Zealand plantations on an average 29-year rotation, largely on land that was historically pasture rather than cleared native forest. Foresters still debate the trade-off: a fast-growing, single-species plantation banks less carbon per tree than an old forest and raises its own biodiversity questions.
PEFC Chain of Custody since 2013
We were the first in our industry to hold it, so every batch of cedar we've bought since carries the paperwork, not just a claim on a website.
Carbon tracked with Planet Mark
Planet Mark certification measures our direct emissions, purchased energy and supply chain impacts, verified against evidence, reported every year and tied to real reduction targets.
Working with The King's Foundation
Through donations and support we work with the Foundation to enhance the learning of people on its training programmes, and our Heritage range was developed in partnership with it.
Ready for EUDR
We already prepare due diligence documentation for our cedar shipments to Europe, ahead of the EU rules applying in full.
Figures draw on published data from PEFC UK, the World Resources Institute, Abodo Wood, the NZ Forest Owners Association, Planet Mark, Accoya, Vastern Timber, Timber Development UK, the Western Red Cedar Lumber Association, Accsys and the European Commission, alongside our own certifications. Ask us for the source of any figure.
Still unsure which timber choice suits you best?
Every Woodpecker greenhouse is built to order. Talk it through with someone who works with this timber every day, or visit our showroom in Staffordshire.