If you’re planning a sauna project—whether it’s a cosy garden retreat or a larger outdoor wellness space—choosing the right sauna cladding is absolutely crucial. That’s where our thermally modified ash comes into its own. This remarkable timber is native British ash that’s been transformed through a completely natural heat treatment process, heated to temperatures exceeding 210 degrees Celsius in a vacuum atmosphere. No chemicals, no nasties, just pure heat and carefully controlled conditions. The result? A timber that’s naturally resistant to rot, decay, and insect damage, with a lifespan of up to 60 years when used externally above ground level. What’s particularly brilliant is that our process is completely chemical-free and powered by our on-site solar farm here in Devon, making it perfectly safe for wellness spaces like saunas where you want nothing but natural materials surrounding you. Fresh from the kiln, it has gorgeous rich chocolate-brown hues that showcase the ash’s distinctive grain patterns, and over time it gradually silvers to a beautiful weathered grey—much like oak or cedar does naturally. You can see this natural weathering process in action on some of our projects, and it’s genuinely stunning. For more comprehensive information about the properties and applications of thermally modified wood, our downloadable technical guide provides excellent technical insight.
Crafted for Calm
One of the most valuable aspects of working with us is our flexibility. We can machine our thermally modified ash to different profiles to suit your specific sauna cladding design requirements. Ask us for our profile pdf by emailing us today. This flexibility is invaluable when you’re working on a unique sauna design, perhaps something curved or a specific architectural style that requires particular detailing. We love a good conversation about what you’re trying to achieve, and we’ll work with you to create the profiles that’ll bring your vision to life. What’s more, we’re particularly proud to welcome smaller orders—we understand that not every project is a massive commercial development. Sometimes you’re just building a single garden sauna, and we don’t believe you should have to buy vast quantities just to access quality British timber. Many sauna builders we work with start with smaller projects and gradually expand, and we’re here to support that journey. Have a look at the stunning work that Graham Cannon and his team create with quality timber —the images throughout this piece showcase his bespoke sauna builds (all photos courtesy of Graham Cannon Saunas), demonstrating just how beautiful a well-crafted outdoor sauna can be when you combine skilled building with excellent sauna cladding materials.
British Grown, Naturally Better
For external sauna cladding, dimensional stability is absolutely critical. Traditional untreated timber can warp, cup, and split when exposed to the extreme conditions around a sauna—the heat radiating from within, the moisture from steam escaping, and then the cold and wet of British winters. Our thermally modified ash excels here because the heat treatment fundamentally alters how the timber interacts with moisture, making the wood much less interested in absorbing water. This means it maintains its shape and dimensions far better than untreated alternatives, with stability improved by up to 60% compared to regular timber. This enhanced stability isn’t just about aesthetics—it’s about maintaining the thermal envelope and ensuring joints stay tight. When cladding boards stay stable, your sauna performs better and requires less maintenance over its lifetime. Architects and designers working on high-performance outdoor wellness spaces are increasingly specifying thermally modified timber precisely because it aligns with modern expectations for both performance and sustainability. For more on why this material works so brilliantly for sauna applications specifically, Neptune Saunas offers a thorough technical guide as to how thermoash is a the perfect product for sauna use.
Crafted for Calm
In a world increasingly concerned with environmental impact, the sustainability credentials of your sauna cladding materials genuinely matter. Our thermally modified ash ticks all the right boxes—it’s British-grown timber, sourced from local woodlands and processed right here in our Devon sawmill. We’re certified with Grown in Britain, which means our timber is fully traceable from forest to finished board. There’s no long-haul shipping of tropical hardwoods, no reliance on chemically-treated imports, and no supporting of questionable forestry practices abroad. Currently, the UK imports around 80% of the wood we use—a statistic that’s frankly astonishing—so every project that specifies British timber helps shift that balance. The thermal modification process itself is remarkably clean, powered by solar energy and using no chemicals whatsoever. The wood that emerges is completely natural, with no chemical runoff, no toxic preservatives, and nothing that could leach out over time. For wellness-focused projects like saunas, this purity of material is genuinely important. Let’s be honest—the British climate isn’t kind to outdoor structures, but thermally modified ash was developed in Northern Europe specifically to handle these challenging conditions. The enhanced rot resistance means you don’t need to worry about the bottom courses of cladding deteriorating from ground splash or persistent damp, and the natural resistance to fungal growth means you won’t see unsightly black mould streaks developing after a few wet months. You can learn more about the benefits of thermally modified timber and its fascinating history and development on our website.
Why Choose Coppice & Crown Sauna Wood
If you’re planning a sauna build and want to explore what thermally modified ash could offer your project, we’d genuinely love to hear from you. Pop over to our sauna timber page to see more about how this material performs in wellness applications. Our team is always happy to discuss your specific sauna cladding requirements, talk through profile options, and provide samples so you can see and feel the quality for yourself. We’re a family-run business, and we genuinely care about helping people create beautiful, lasting projects with British timber. Building a sauna is an investment in wellbeing, relaxation, and connection with nature, and the materials you choose should reflect that long-term thinking, combining beauty, durability, and environmental responsibility. Our thermally modified ash delivers on all three counts, offering a genuinely sustainable, chemical-free solution that’ll serve you faithfully for up to 60 years. So whether you’re a professional builder, an architect specifying materials, or a homeowner with dreams of a garden sauna, we’re here to help make it happen with the very best of British timber. After all, there’s something rather wonderful about relaxing in a space built from trees that grew just down the road, transformed through ancient techniques into sauna cladding that’ll outlast us all. Ready to discuss your sauna project? Get in touch with our team at UK Hardwoods to explore how thermally modified ash can work for you.
