ThermoWood Species Database
The base timber species commonly used for thermal modification (ThermoWood), with the treatment class, typical mass loss, durability achieved and ideal applications for each.
Revision history
- — Site-wide audit — all tabulated values re-checked against listed sources
ThermoWood is not a species — it is a chemical-free heat treatment (typically 180–215°C under controlled steam) that permanently changes the wood's cell structure. The result: greatly reduced moisture movement, improved decay resistance, and a darker through-colour. Thermo-S (~190°C) targets stability for interior and shaded use; Thermo-D (~212°C+) targets durability for exterior cladding and decking. Mass loss during treatment is the key indicator of how far the modification has gone.
| Base Species ↕ | Treatment Class ↕ | Typical Mass Loss ↕ | Durability Achieved ↕ | EMC Reduction ↕ | Best For ↕ |
|---|---|---|---|---|---|
| Scots PinePinus sylvestris | Thermo-D | 8-12% | Class 2 (Durable) | ~50% | Cladding, decking, sauna |
| Norway SprucePicea abies | Thermo-D | 8-12% | Class 2-3 | ~45% | Cladding, garden structures |
| Radiata PinePinus radiata | Thermo-D | 9-12% | Class 2 | ~50% | Decking, cladding |
| AshFraxinus excelsior | Thermo-D | 7-10% | Class 1-2 | ~50% | Decking, flooring, furniture |
| PoplarPopulus spp. | Thermo-S / Thermo-D | 8-12% | Class 2-3 | ~45% | Cladding, lightweight panels |
| BirchBetula spp. | Thermo-D | 8-11% | Class 2 | ~48% | Furniture, interior, panels |
| OakQuercus spp. | Thermo-D | 6-9% | Class 1 | ~45% | Flooring, exterior furniture |
| MapleAcer spp. | Thermo-D | 7-10% | Class 2 | ~48% | Flooring, joinery |
| AspenPopulus tremula | Thermo-S | 8-11% | Class 2-3 | ~45% | Sauna interiors, cladding |
| EucalyptusEucalyptus spp. | Thermo-D | 7-10% | Class 1-2 | ~48% | Decking, cladding |
ThermoWood tools
Related reading & species
Sources
- Finnish ThermoWood Association — ThermoWood Handbook — thermowood.fi
- EN 350 durability classification
Common questions
What is ThermoWood in simple words?
It is normal wood heated to around 200°C with steam and no chemicals. The heat changes the wood so it takes in much less water. That makes it more stable and much slower to rot.
Does heat treatment make wood harder?
No — slightly the opposite. The treatment makes wood a little more brittle and a bit less hard. What you gain is stability and rot resistance, not strength. Do not use ThermoWood for load-bearing beams.
Which species work best for thermal treatment?
Pine, spruce, ash and radiata pine are the common ones. Softwoods are used for cladding and decking; thermo ash is popular where a darker, richer look is wanted.
How long does ThermoWood last outside?
Properly treated ThermoWood reaches Durability Class 2, which in most climates means decades of outdoor use without preservative chemicals. The surface still greys in the sun unless you oil it.