Thermally modified timber undergoes a specialist heat treatment process where the wood is carefully heated (usually between 160°C and 220°C) in a controlled, oxygen-free environment. This alters the internal structure of the timber at a cellular level — reducing its moisture content, increasing stability, and enhancing its natural resistance to rot, decay and insects.
Crucially, this process uses no chemicals, just heat and steam. The result is timber that is long-lasting, dimensionally stable, and stunningly rich in colour — making it ideal for decking, cladding, and other exposed applications.
Why We Love Thermally Modified British Ash for Timber Decking
At UK Hardwoods, we specialise in using thermally modified native ash — a homegrown hardwood with exceptional grain character and strength. It offers:
Natural beauty: Ash has a lively, expressive grain that comes to life with thermal treatment, taking on a deep caramel or chocolate hue.
Superb durability: Thermal modification gives it durability comparable to tropical hardwoods — without the environmental cost.
Enhanced stability: Less movement, less cupping, less splitting — ideal for the UK’s damp winters and warm summers.
Eco integrity: It’s sourced and crafted right here in Britain. No tropical forests harmed. No long-haul shipping. Fully Grown in Britain certified.
Sustainable Outdoor Living Starts with Smarter Materials
British architects, landscape designers and homeowners are increasingly choosing thermally modified ash decking for its blend of performance and eco credentials. It aligns perfectly with the net zero goals of forward-thinking builds, especially when paired with other low-carbon choices like lime render, sheep’s wool insulation, or natural stone.
Unlike imported softwoods that are pressure-treated with harsh chemicals, or tropical hardwoods with questionable provenance, our ash is fully traceable, locally grown, and crafted in our North Devon sawmill with care and intention.
What to Expect from Your Timber Decking Over Time
Thermally modified ash will naturally silver down with exposure to sunlight — much like oak or cedar. Some clients love this weathered look, while others prefer to maintain the rich brown tones with regular applications of a UV-protective oil. Either way, your timber decking will age gracefully, developing character with every season.
British Craftsmanship, Built to Last
We’re currently preparing a limited run of thermally modified ash for upcoming cladding and timber decking projects this autumn. If you’d like to reserve stock or request samples, please get in touch — we’d love to help you bring your project to life with local, sustainable timber.
