- ThermoWood pine is the best wood for sauna interiors — low thermal conductivity keeps board surfaces comfortable to touch at high temperatures, resin-free, dimensionally stable, and no chemical treatment required.
- Nordic spruce is the traditional and most affordable sauna interior timber — light colour, mild fragrance, good performance in both dry and steam sauna conditions.
- Avoid resinous species (standard pine, larch, Douglas fir) for sauna interiors — high temperatures cause resin to exude, creating sticky surfaces and potential skin contact issues.
- For outdoor sauna exterior cladding, Siberian larch and ThermoWood are the strongest choices — naturally durable, low maintenance, excellent performance in UK weather.
- Charred timber is increasingly popular for outdoor sauna exteriors — bold black finish, zero maintenance, 25–40 year service life.
Choosing the right wood for a sauna is one of the most important decisions in the build — and one where the wrong choice creates real problems in service. The requirements for sauna timber are fundamentally different from standard interior joinery or exterior cladding: the wood must perform reliably in a high-heat, high-humidity environment, stay comfortable against skin at temperatures of 70–100°C, and remain stable through thousands of heat-and-cool cycles over the life of the sauna. This guide covers the best timber species for both sauna interiors and outdoor sauna exteriors, with honest comparisons across performance, cost, and where to buy in the UK.
ThermoWood pine tongue and groove interior sauna cladding — the warm honey-brown colour, consistent grain, and comfortable surface temperature make ThermoWood the most specified sauna interior timber for contemporary UK builds.
Interior vs Exterior — Two Different Timber Requirements
The single most important thing to understand about sauna timber is that interior and exterior requirements are completely different — and the species that excels in one role can actually be problematic in the other.
Sauna interior timber must perform in a hot, humid environment where it will be in close proximity to — and sometimes contact with — skin. The critical requirements are low thermal conductivity (so board surfaces don't become uncomfortably hot to touch), no resin exudation at high temperatures (resin melts and becomes sticky at sauna temperatures), good dimensional stability through repeated heat-and-cool cycles, and no chemical treatments that could off-gas in a confined heated space.
Outdoor sauna exterior cladding faces entirely different conditions — UK weather, moisture cycling, UV exposure, and biological decay risk. Here the requirements are natural durability or thermal modification for decay resistance, dimensional stability against UK seasonal moisture variation, and a species that performs reliably with minimal maintenance over decades.
The most common sauna timber mistake is specifying the same species for both interior and exterior. Siberian larch — an excellent exterior cladding timber — is unsuitable for sauna interiors due to resin exudation at high temperatures. Standard pine is similarly problematic inside. Conversely, interior-grade tongue and groove spruce is not appropriate for unprotected exterior use without treatment. Specify correctly for each application.
Best Wood for Sauna Interiors
Indoor sauna cladding — tongue and groove timber panels on walls and ceiling. Species choice for the interior directly affects comfort, safety, and long-term performance in the high-temperature environment.
ThermoWood for Saunas — Why It's the Top Choice
ThermoWood interior sauna cladding — the thermal modification process removes resins and reduces thermal conductivity, making boards comfortable to touch even at 90°C sauna temperatures.
The thermal modification process that makes ThermoWood an excellent exterior cladding material also makes it the best sauna interior timber. Heating Nordic pine to 185–215°C drives out the resins permanently — removing the sticky, potentially uncomfortable resin exudation that affects untreated pine at high temperatures. The process also reduces the wood's thermal conductivity, meaning board surfaces heat up more slowly and stay at a more comfortable temperature to touch than untreated softwoods. And the dimensional stability improvements from thermal modification are particularly valuable in a sauna — the repeated cycles of high heat and high humidity that a sauna undergoes would cause significant movement in untreated timber over years of use.
We stock ThermoWood tongue and groove V-joint 19x140mm specifically suited for sauna interior lining — the interlocking profile creates a seamless flush surface with no exposed fixings, and the 140mm board width gives a clean, contemporary result on sauna walls and ceilings. The warm honey-brown colour of ThermoWood is particularly suited to the sauna aesthetic — warmer and more characterful than the pale white of spruce while avoiding the resin issues of standard pine.
For a detailed comparison of ThermoWood versus cedar for sauna applications see our ThermoWood sauna vs cedar sauna guide, and for the best ThermoWood profile for different sauna types see our best ThermoWood profile for garden saunas guide.
Best Wood for Outdoor Sauna Exterior Cladding
Siberian larch exterior sauna cladding — the natural grain and silver-grey weathering of larch creates an excellent outdoor sauna aesthetic that sits naturally in a UK garden setting and requires minimal maintenance.
The exterior of an outdoor sauna faces exactly the same conditions as any other UK exterior timber cladding — rain, UV, frost, and biological decay risk. The same species that perform well on a house extension or garden room perform well on a sauna exterior. The choice comes down to the same factors: natural durability, maintenance commitment, and visual preference.
Siberian larch is the most popular outdoor sauna exterior species — its natural durability requires no preservative treatment, it weathers to an attractive silver-grey, and its distinctive grain and warm golden-yellow colour create an excellent sauna exterior aesthetic. Available in shadow gap, shiplap, and feather edge profiles from our Siberian larch range.
ThermoWood offers even greater dimensional stability and zero maintenance requirement — particularly suited to outdoor saunas where the interior humidity cycling creates additional moisture stress on the exterior cladding from the inside. Available in shadow gap, shiplap, and rainscreen profiles from our ThermoWood range.
Weathered Timber — The Natural Outdoor Sauna Look
Weathered timber outdoor sauna exterior — the silver-grey patina of naturally weathered larch or ThermoWood requires no ongoing maintenance and creates an authentic Scandinavian sauna aesthetic that suits UK garden settings perfectly.
The silver-grey weathered finish is one of the most popular outdoor sauna exterior aesthetics in the UK — and for good reason. Left unfinished, Siberian larch and ThermoWood both weather to a consistent silver-grey that requires absolutely no ongoing maintenance. The result looks authentic, considered, and timeless rather than tired — exactly the aesthetic associated with traditional Scandinavian sauna culture.
For outdoor saunas specifically, the zero-maintenance weathered finish is particularly appealing — a garden sauna is an occasional-use structure that benefits enormously from a cladding that looks after itself. Specifying ThermoWood or larch and leaving it to weather naturally removes any ongoing maintenance obligation from the exterior entirely, allowing you to focus maintenance attention on the interior where it matters more.
Charred Timber Outdoor Saunas — The Bold Alternative
Deep charred timber exterior on a UK outdoor sauna — the bold black carbonised finish requires zero maintenance and creates a dramatic visual contrast against the garden landscape that has made charred outdoor saunas one of the most searched sauna designs in the UK.
Charred timber outdoor saunas have become one of the most popular garden building trends in the UK — the combination of deep black exterior, warm timber interior, and the steam and heat of the sauna experience creates a powerful sensory contrast that resonates strongly with contemporary outdoor living aesthetics.
The Shou Sugi Ban inspired deep charring process creates a carbonised exterior surface that requires zero ongoing maintenance — no oiling, staining, or treatment of any kind throughout the 25–40 year service life. The black exterior also has practical advantages for an outdoor sauna: the dark surface absorbs solar heat, potentially reducing the energy required to heat the sauna in cooler months, and the carbonised layer's excellent moisture resistance suits the humid microclimate immediately around an outdoor sauna structure.
Shou Sugi Ban inspired charred timber on a UK outdoor sauna — the bold black exterior and warm timber interior create the most popular contemporary outdoor sauna aesthetic in the UK. Zero maintenance throughout the full service life.
Browse our full charred timber cladding range for available profiles and finishes for outdoor sauna exteriors.
Sauna Timber Comparison — Interior & Exterior
| Timber | Interior use | Exterior use | Cost per m² | Maintenance |
|---|---|---|---|---|
| ThermoWood pine | ✓ Best choice | ✓ Excellent | £45–£65 | None required |
| Nordic Spruce | ✓ Traditional choice | ⚠️ Treat every 2–3 yrs | £20–£35 | Regular treatment outside |
| Siberian Larch | ✗ Avoid — resinous | ✓ Excellent | £35–£70 | None required outside |
| Western Red Cedar | ✓ Good — aromatic | ✓ Good | £60–£90 | Oil every 3–5 yrs |
| Aspen | ✓ Hypoallergenic | ✗ Not recommended | £55–£80 | Interior only |
| Charred Timber | ✗ Not for interiors | ✓ Bold, zero maintenance | £75–£130 | None required |
| Standard Pine | ✗ Avoid — resinous | ✗ Not durable | £15–£25 | Frequent treatment needed |
For the best overall sauna build — use ThermoWood pine tongue and groove for the interior walls and ceiling, and Siberian larch or ThermoWood shadow gap for the exterior cladding. This combination delivers the best interior comfort, zero maintenance on both surfaces, and a Scandinavian aesthetic that suits contemporary UK garden saunas perfectly. For a bold exterior — deep charred larch outside with ThermoWood interior is the most striking combination. For a budget sauna — Nordic spruce inside and larch outside gives excellent performance at the most accessible cost.
What is the best wood for a sauna interior in the UK?
ThermoWood pine is the best wood for sauna interiors in the UK. Its low thermal conductivity keeps board surfaces comfortable to touch at high temperatures, it is resin-free after thermal modification, dimensionally stable through heat cycles, and requires no chemical treatment. Nordic spruce is the traditional and most affordable alternative — light colour, mild fragrance, and good performance in both dry and steam sauna conditions.
Can you use Siberian larch inside a sauna?
No — Siberian larch is not recommended for sauna interiors. Its high resin content causes resin to exude at high temperatures, creating sticky surfaces and potential skin contact issues. Use ThermoWood pine or Nordic spruce for sauna interiors. Siberian larch is however an excellent choice for outdoor sauna exterior cladding.
What wood is best for an outdoor sauna exterior?
Siberian larch and ThermoWood are the two strongest choices for outdoor sauna exterior cladding in the UK. Both offer natural or thermally modified durability without preservative treatment, weather beautifully to silver-grey, and have service lives of 20–40 years. Charred timber is increasingly popular for outdoor saunas where a bold black exterior is wanted — zero maintenance and exceptional weather resistance.
What is ThermoWood sauna timber?
ThermoWood sauna timber is Nordic pine thermally modified at 185–215°C using heat and steam — no chemicals. The process drives out resins, reduces thermal conductivity, and improves dimensional stability. Available in tongue and groove for sauna interiors and shadow gap, shiplap, and rainscreen profiles for exterior sauna cladding.
How much does sauna timber cladding cost in the UK?
Nordic spruce tongue and groove for sauna interiors costs approximately £20–£35 per m². ThermoWood tongue and groove costs approximately £45–£65 per m². For outdoor sauna exterior cladding, Siberian larch costs £35–£70 per m² and ThermoWood costs £55–£95 per m². A typical 4-person garden sauna with 20m² interior lining and 25m² exterior cladding costs £1,800–£4,200 in timber materials.
Sauna Timber — Interior Lining & Exterior Cladding, UK Stock
We supply ThermoWood tongue and groove for sauna interiors, and Siberian larch, ThermoWood, and charred timber for outdoor sauna exteriors — all FSC and PEFC certified from UK stock with nationwide delivery in 7–14 days. Send us your sauna dimensions for a precise material quote.
