ThermoWood Birch Thermo-D VS ThermoWood Ash Thermo-D
- Leads on machining ease in this pair
- Harder wear surface
- Solid choice where its profile fits the project
Visual comparison
Winner by category
There isn't one universally best wood — there's a best wood for each purpose.
| Category | Winner |
|---|---|
| Durability | Tie |
| Stability | Tie |
| Hardness | ThermoWood Ash Thermo-D |
| Strength (MOR) | Tie |
| Stiffness (MOE) | ThermoWood Ash Thermo-D |
| Flame spread | Tie |
| Machining ease | ThermoWood Birch Thermo-D |
| Lightness | ThermoWood Ash Thermo-D |
Engineering data
| Property | ThermoWood Birch Thermo-D | ThermoWood Ash Thermo-D |
|---|---|---|
| Janka Hardness | 1210UNV lbf | 1320UNV lbf |
| Density | 0.62ITWA g/cm³ | 0.55ITWA g/cm³ |
| MOE | 12.0ITWA GPa | 13.3ITWA GPa |
| MOR | 95.0ITWA MPa | 90.0ITWA MPa |
| Durability | Class 2 Durable (treated) | Class 2 Durable (treated) |
| Stability | Good | Good |
| Fire (E84) | Not classified | Not classified |
| Radial Shrink | 1.6ITWA % | 1.7ITWA % |
| Tangential Shrink | 3ITWA % | 3.2ITWA % |
| T/R Ratio | 1.88 | 1.88 |
Figures carry the same source status as the species pages they come from — verified where cited, indicative where marked.
Best for
| Application | Recommended | Suitability |
|---|---|---|
| Outdoor decking / pergola | 🥇 ThermoWood Birch Thermo-D | ★★★★☆ |
| Exterior cladding | 🥇 ThermoWood Birch Thermo-D | ★★★☆☆ |
| Flooring / wear surfaces | 🥇 ThermoWood Ash Thermo-D | ★★★☆☆ |
| Furniture / interior joinery | 🥇 ThermoWood Birch Thermo-D | ★★★☆☆ |
| Structural / load-bearing | 🥇 ThermoWood Birch Thermo-D | ★★★☆☆ |
| Sauna / wet interiors | 🥇 ThermoWood Birch Thermo-D | ★★★★☆ |
Advantages & limitations
ThermoWood Birch Thermo-D
Advantages relative to ThermoWood Ash Thermo-D
Limitations relative to ThermoWood Ash Thermo-D
ThermoWood Ash Thermo-D
Advantages relative to ThermoWood Birch Thermo-D
Limitations relative to ThermoWood Birch Thermo-D
Recommendation
Choose ThermoWood Birch Thermo-D if…
- Exterior cladding, interior panelling and flooring, sauna benches and interiors where the specific thermally modified birch profile matches the specification
- Furniture and joinery where the birch grain and appearance are the aesthetic preference
Choose ThermoWood Ash Thermo-D if…
- Decking (Ash's signature thermally modified application), garden furniture and interior flooring where the ash figure is the design intent
- Exterior cladding and joinery where either species could serve and the ash grain is preferred
Frequently asked questions
Which is more durable, ThermoWood Birch Thermo-D or ThermoWood Ash Thermo-D?
Neither — both carry the same EN 350 rating (Class 2, Durable (treated)). Outdoors, movement will not separate them either — 3.0% against 3.2% tangential. The practical difference is weight: ThermoWood Birch Thermo-D runs 0.62 g/cm³ against 0.55, so ThermoWood Ash Thermo-D is the easier fix overhead and the cheaper one to freight.
Which wood is better for outdoor use?
Both are EN 350 Class 2, and tangential movement runs 3.0% for ThermoWood Birch Thermo-D against 3.2% for ThermoWood Ash Thermo-D — close enough that decay resistance will not choose between them, and ThermoWood Birch Thermo-D holds its dimension marginally better. ThermoWood Ash Thermo-D gives the harder wearing surface at 1,320 lbf and the lighter section at 0.55 g/cm³; ThermoWood Birch Thermo-D leads on machining ease — traffic and handling favour Ash, cutting and shaping favour Birch.
Is ThermoWood Birch Thermo-D harder than ThermoWood Ash Thermo-D?
No — ThermoWood Ash Thermo-D is harder (Janka 1320 vs 1210 lbf).