What Is Thermo-Ash Cladding?

Thermo-Ash is a thermally modified hardwood, produced by heating ash timber to high temperatures in a controlled environment. This process alters the structure of the timber, improving its resistance to moisture, reducing movement, and increasing durability without the use of chemical treatments. As a result, Thermo-Ash cladding offers a stable and reliable solution for exterior applications where timber is exposed to changing weather conditions.

Key Benefits of Thermo-Ash Cladding

Thermo-Ash cladding offers several practical and aesthetic advantages:

• Improved stability with reduced risk of warping or movement
• Enhanced durability for exterior use
• Consistent colour and grain for a clean, modern finish
• Smooth surface finish, ideal for contemporary designs
• Thermal modification without chemicals, supporting a more sustainable approach
• Supplied pre-oiled for added protection and reduced preparation time during installation

These qualities make Thermo-Ash particularly well suited to modern architectural projects.

Available Profiles

Thermo-Ash cladding is available in a selection of precision-milled profiles, each designed to achieve a different visual finish and installation style. At Southgate Timber, the current Thermo-Ash cladding range includes:

20 x 132mm C34

The 20 x 132mm C34 Thermo-Ash cladding profile is designed primarily for vertical installation, creating a clean, linear appearance with subtle shadow lines.

• Hidden fix system for a seamless finish
• Designed to leave a consistent shadow gap between boards
• Ideal for modern façades and garden rooms
• Creates a structured, vertical aesthetic

This profile is particularly effective when used across full elevations to emphasise height and architectural lines

20 x 132mm C6

The 20 x 132mm C6 Thermo-Ash cladding profile is designed for horizontal installation, offering a more contemporary, architectural finish.

• Installed using hidden clips
• Creates a tighter, more refined shadow gap (approx. 4mm)
• Smooth, uniform appearance across long runs
• Well suited to modern residential and landscaping projects

Horizontal installation helps visually widen a space and is often used in garden rooms, extensions and feature walls.

Thermo-Ash Décor Rhomb Tiles (Internal Feature Profile)

In addition to exterior cladding, Thermo-Ash is also available as decorative rhombus tiles for internal applications.

• Designed for feature walls and interior finishes
• Distinct angled profile for a geometric, high-end look
• Can be installed in repeating or patterned layouts
• Brings the warmth of Thermo-Ash into interior spaces

This provides an opportunity to create a consistent design aesthetic between exterior and interior environments.

Installation: Fixings & Clips

Thermo-Ash cladding can be installed in both vertical and horizontal orientations, depending on the chosen profile. The C34 is used for vertical installation, while the C6 is designed for horizontal applications, each creating a different visual effect.

Its typically installed using hidden fixing systems, which help achieve a clean, uninterrupted finish while maintaining correct spacing and airflow. For profiles such as the 20 x 132mm C6, a dedicated fixing solution, the B1-1 cladding clip, is used. These clips allow boards to be securely fixed in place while remaining hidden from view, creating a seamless external appearance.

Using the correct fixing system ensures:

• A secure and long-lasting installation
• Consistent spacing between boards
• Proper ventilation behind the cladding
• A high-quality, professional finish

Thermo-Ash Cladding vs Other Timber Cladding Options

When compared with other cladding timbers, Thermo-Ash offers a balanced combination of performance and aesthetics.

• Compared to Western Red Cedar, Thermo-Ash offers a more uniform appearance and darker tone
• Compared to Larch, it provides greater stability and reduced movement
• Compared to other thermally modified timbers like Thermowood Pine, Thermo-Ash offers a premium hardwood finish with a smoother appearance.

This makes it a versatile choice across a range of project types.

Matching Thermo-Ash Decking

For a cohesive outdoor design, our stock range not only includes just Thermo-Ash cladding, but Thermo-Ash decking to pair with too, allowing you to create a consistent finish across vertical and horizontal surfaces.

Maintenance & Lifespan

Thermo-Ash cladding is designed to perform well in outdoor environments. The thermal modification process improves durability, while the pre-oiled finish helps protect the timber from the outset. Like all timber, it can be left to weather naturally over time or maintained with oils to preserve its original colour. For ongoing maintenance, we recommend using the Thermory Oil Dark to re-oil the surface and maintain the rich, consistent finish of the timber.

Where Is Thermo-Ash Cladding Best Used?

Thermo-Ash cladding is suitable for a wide range of applications, including:

• Garden rooms and outbuildings
• Residential extensions
• Feature walls and façades
• Contemporary screening

Its clean finish and stability make it particularly well suited to modern architectural designs.

FAQ’s

Is Thermo-Ash cladding suitable for UK weather?

Yes, Thermo-Ash cladding performs well in the UK climate. The thermal modification process improves the timber’s resistance to moisture and reduces movement caused by changes in temperature and humidity, making it a reliable choice for exterior applications.

Is Thermo-Ash better than Cedar?

Both are high-quality cladding options. Thermo-Ash offers a more uniform appearance and enhanced stability, while Cedar is lighter and naturally durable.

Does Thermo-Ash cladding need treatment?

Thermo-Ash cladding is supplied pre-oiled, which provides initial protection. Additional treatment can be applied over time to maintain colour if desired.