Thermowood cladding is increasingly specified for British homes, garden rooms and commercial buildings because it offers a warm, consistent appearance and improved dimensional stability. However, the name describes a manufacturing process as well as a finished material, and products can differ in species, grade, profile and treatment class. This guide explains what to compare before requesting samples or project pricing, without treating every thermally modified board as interchangeable.
What is Thermowood cladding?
Thermowood is timber modified using a controlled process involving heat, steam and carefully managed conditions. The treatment changes properties within the wood rather than relying on a conventional preservative impregnation. It typically darkens the timber, reduces its tendency to absorb moisture and improves dimensional stability compared with the unmodified source material.
The term Thermowood may refer to products made under a particular process or certification system, while ‘thermally modified timber’ is a broader description. When comparing quotations, confirm the actual species, modification process, treatment class, grade and technical documentation supplied. Similar-looking brown boards do not necessarily have the same declared properties or intended applications.
For cladding, thermally modified softwoods are machined into profiles such as tongue and groove, shadow gap, rainscreen battens and board-on-board systems. The chosen board must still be appropriate for its location, orientation and complete wall design.
- Modified using controlled heat and steam
- Typically more dimensionally stable than the source timber
- Warm brown colour with a clean contemporary character
- Available in several external cladding profiles
Why do architects and homeowners choose it?
Consistency is a major part of Thermowood’s appeal. Its toasted brown tone can create a calm, unified elevation, while the visible grain retains the warmth expected from real timber. It works particularly well with dark window frames, render, stone and metal details, making it suitable for contemporary extensions as well as larger education, leisure and workplace projects.
Improved stability is also valuable on a façade. All timber responds to changing moisture conditions, but thermal modification can reduce movement compared with untreated material. That can support crisp machining and controlled joint lines when the product is correctly designed, stored and installed.
The process does not remove the need for good detailing. A drained and ventilated cavity, suitable fixings, appropriate clearances and properly resolved openings remain essential. Thermowood should be selected as one component within a façade system, not as a shortcut around sound construction.
What does Thermowood look like?
New Thermowood cladding generally has an even mid-to-deep brown colour, sometimes described as caramel or toasted. The exact tone and grain depend on the source species, modification level, surface texture and finish. A smooth-planed board appears more refined, while a brushed or textured face can emphasise the grain and create stronger visual depth.
Natural variation remains part of the material. Boards may show knots, grain changes and colour differences according to grade. A representative sample set is therefore more useful than a single perfect board, especially when the elevation is large or the design expects close visual consistency.
Profile and orientation change the overall effect. Narrow vertical boards emphasise height and rhythm, while horizontal tongue and groove can make a compact building feel wider. Open-jointed rainscreen arrangements create deeper shadow lines but require the backing layer and cavity to be designed for the intended exposure.
Does Thermowood cladding stay brown?
Uncoated Thermowood does not permanently retain its initial brown colour. Exposure to ultraviolet light and weather gradually changes the surface towards silver-grey, as happens with many exterior timbers. The transition can vary across a building because sunny, exposed elevations weather differently from areas protected by eaves or neighbouring structures.
Some projects welcome that natural patina and choose Thermowood for its stability and grain rather than its day-one colour. Others use a compatible pigmented or UV-resistant exterior finish to retain more of the brown appearance. A pre-weathered finish may be considered where a more uniform grey is wanted from installation.
Any coating introduces inspection and maintenance requirements. Confirm compatibility, preparation, application and recoat guidance with the finish manufacturer and board supplier. The best decision starts with the appearance expected several years after completion, not only the colour of a fresh sample.
Thermowood cladding maintenance
Maintenance depends on the chosen finish, exposure and desired appearance. An unfinished façade intended to weather naturally may not require decorative recoating, but it should still be inspected for damage, persistent moisture traps, blocked ventilation, loose boards and failed junctions. Dirt and biological growth should be assessed using guidance appropriate to the specific product rather than aggressive generic cleaning methods.
A coated façade needs a planned inspection cycle. Recoating intervals cannot responsibly be reduced to one universal number because they vary with product, colour, surface preparation, orientation and local weather. South-facing walls and exposed coastal sites may behave differently from sheltered elevations in Bath, Bristol or inland Wiltshire.
Access should be considered at design stage. Maintaining a ground-floor garden room is straightforward compared with recoating a multi-storey commercial elevation. If low intervention is a priority, discuss natural weathering and factory-finished options before the profile and colour are approved.
Which profiles suit Thermowood?
Thermowood can be machined into many familiar cladding profiles. Shadow-gap and tongue-and-groove boards create a neat architectural surface. Board-on-board systems provide deeper relief and can reference agricultural buildings, while open rainscreen battens produce strong linearity for entrances, feature panels and complete elevations.
The right profile depends on orientation, exposure and architectural intent. A product approved for horizontal installation should not automatically be rotated vertically. Confirm usable face, installed cover, fixing zone and whether the selected profile is intended for open or closed joints.
Corners, window reveals, cills, heads, ventilation openings and the base of the cladding affect both appearance and quantity. Resolving these details early reduces improvised trims on site and makes competing quotations easier to compare.
What affects Thermowood cladding prices?
Thermowood cladding prices vary with source species, modification process, grade, dimensions, profile, visible cover, length mix and order quantity. Surface texturing, factory coating, fire treatment or bespoke machining can add cost, as can project-specific certification and documentation.
A headline square-metre rate does not always represent the completed supply requirement. Allow for profile overlap, cutting waste, trims, fixings, coating, delivery and access constraints. A board’s nominal width may be greater than its installed cover, so compare the area actually covered rather than the overall dimension.
For larger projects, provide elevation drawings, approximate quantities, site location, preferred orientation, programme and known technical requirements. For a smaller shed or garden room, dimensions, photographs and a sketch may be enough to develop an initial shortlist. Both deserve a project-specific comparison rather than a generic online price.
Is Thermowood right for your project?
Thermowood is a strong candidate where stable machining, consistent colour and a contemporary natural finish are important. It can suit a compact garden studio, a house extension or a substantial commercial façade. It may be less appropriate where the brief expects the fresh brown colour to remain unchanged without maintenance, or where the selected product cannot provide the documentation required by the project.
Compare it with credible alternatives rather than choosing from photographs alone. Cedar may offer richer natural colour variation and a lighter feel, while larch provides stronger grain and a more expressive character. Samples of the proposed grades and profiles make the differences clearer than species names.
The Cladding Centre can help compare Thermowood profiles, finishes and supply options for projects across the South West. The same considered approach applies whether you need a few boards for an outbuilding in Gloucestershire or a documented package for a commercial development in Wiltshire.
- Confirm species, process, grade and intended application
- Decide whether natural silvering or maintained brown is preferred
- Compare installed cover and complete supply costs
- Check profile orientation and project documentation
- Request representative samples before committing