Benefits of Thermally Modified Timber

Thermal modification looks good and does good, enabling creative use of locally-grown timber for cladding, decking and other uses
Vastern Timber
by Vastern Timber
10th October 2022

Thermal modification is a process that transforms fast-grown wood into stable, durable timber. This thermally modified timber is perfect for a range of outdoor uses, such as external cladding and decking.

As we face a climate crisis, people are asking more questions about where their construction materials are coming from and what impact they have. And rightly so.

Using timber can help to reduce the carbon cost of your project – but building with locally-grown wood is even better. It means less mileage, less CO2 emissions, and more support to keep UK woodlands thriving.

Products like Brimstone thermally-modified timber tick all of these environmental and performance boxes. Brimstone is made from locally-grown wood, so you know exactly where it’s from, and it’s durable because it’s thermally modified.

What is thermally modified timber?

In a nutshell, thermal modification is a toxin-free heating process that delivers high-quality timber products.

To create Brimstone, we heat our wood to over 200°C. This alters the cell structure of the timber so that it can no longer absorb water – so, there’s much less risk of bending, warping and decay.

Brimstone ash thermally modified timber

Brimstone ash is a stylish, largely knot-free timber in a deep chocolate colour. It’s suitable for cladding, decking and other joinery

The thermal modification process releases natural chemicals that darken the colour of the wood, giving it a consistent, attractive finish.

A local and low-impact alternative

At Brimstone, we use thermal modification to turn local timber into durable wood for external cladding and decking – but durability wasn’t our only goal.

Over the years, the timber we grow in Britain fell out of fashion and our once-thriving furniture industry, for instance, has all but disappeared. The UK is now the second biggest importer of wood globally, behind only China.

So, we wanted to find a way to bring British species like ash, poplar and sycamore back into popular use, and in the process revitalise our woodlands and support the local economy.

Thermally modifying timber allows us to do exactly that. Our range offers a great alternative to imported hardwood cladding and decking. Instead of using timber that’s been transported thousands of miles, we use wood that’s growing just down the road.

Brimstone ash timber cladding

Vastern’s Brimstone ash thermally modified timber used on a Scandi-inspired self build project

Take Brimstone ash, for example. It’s an ideal alternative to Canadian cedar, which has become very expensive, or Siberian larch, which is now subject to trade bans. And because it’s made with responsibly managed British wood, self builders and renovators can be confident they’re helping to keep trees and wildlife thriving for future generations, so it’s a win-win.

Is thermally modified timber cheaper than other woods?

This is a question we get asked a lot. Generally, the price of locally grown, thermally-modified wood is competitive to imported hardwoods – particularly with current exchange rates.

So, if you want the crisp look of Canadian cedar, without the road miles and hefty price tag, British thermally-modified timber is a cost effective alternative.

Is thermally modifying timber an eco-friendly process?

You might think that a process which involves 200°C heat has downsides, but here’s the thing: it’s all natural. There are no nasty additives or chemicals, just heat and steam.

Extension project with Brimstone timber cladding

This extension project features Brimstone poplar cladding for a fresh contemporary look

We have a thermal modification plant at our sawmill to make Brimstone, so there’s no extra road miles or transportation either. The process does use energy, of course, but we plan to run our Brimstone production plant entirely using renewables by the end of this year.

How can I be sure where my timber comes from?

If you’re looking for lower-impact materials, then you need to understand the provenance of the products you’re considering and look for suppliers who are committed to reducing the carbon cost of construction.

The timber we use for Brimstone is GIB (Grown in Britain) certified, and comes from well-managed woodlands – mostly within 100 miles of our sawmill. We’re also transparent about our impact, with our Environmental Product Declaration easy to find at the top level of our website.

Going forward, we hope more people will ask questions about where their timber comes from. It’s vital today and for the future of our woodlands.


Tom Barnes is managing director of Vastern Timber. He has over 25 years’ experience in the timber trade and is the creator of Brimstone, the first and only modified wood to be grown and manufactured in the UK. Find out more about Brimstone thermally-modified timber >

Main image: The owners of this Scandi-style build wanted to create a low-impact home. They chose Brimstone ash cladding to cover their Honk Fusion cross-laminated timber superstructure

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