Home / Wood Compare / Thermowood Birch ThermoD vs Thermowood Ash ThermoD
Professional Comparison · Verified Engineering Data · Updated 19 July 2026
Thermowood Birch ThermoD VS Thermowood Ash ThermoD
Which wood is better for your project? Scores are computed from the verified figures on each species page — how we score.
🥇
Thermowood Birch ThermoD
62/100 Library Score
🪵Hardwood🌧Outdoor💧Moisture Stable
- Leads on stiffness, machining ease, lightness — a narrow but consistent edge
🥈
Thermowood Ash ThermoD
56/100 Library Score
🪵Hardwood🌧Outdoor💧Moisture Stable
- Harder wear surface
- Solid choice where its profile fits the project
Visual comparison
Thermowood Birch ThermoDThermowood Ash ThermoD
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 ThermoD |
| Strength (MOR) | Tie |
| Stiffness (MOE) | Thermowood Birch ThermoD |
| Flame spread | Tie |
| Machining ease | Thermowood Birch ThermoD |
| Lightness | Thermowood Birch ThermoD |
Engineering data
| Property | Thermowood Birch ThermoD | Thermowood Ash ThermoD |
|---|---|---|
| Janka Hardness | 1210ITWA lbf | 1320ITWA lbf |
| Density | 0.62ITWA g/cm³ | 0.66ITWA g/cm³ |
| MOE | 12.0ITWA GPa | 11.5ITWA GPa |
| MOR | 95.0ITWA MPa | 90.0ITWA MPa |
| Durability | Class 2 Durable (treated) | Class 2 Durable (treated) |
| Stability | Good | Good |
| Fire (E84) | Class C indicative | Class C indicative |
| 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 ThermoD | ★★★★☆ |
| Exterior cladding | 🥇 Thermowood Birch ThermoD | ★★★☆☆ |
| Flooring / wear surfaces | 🥇 Thermowood Ash ThermoD | ★★★☆☆ |
| Furniture / interior joinery | 🥇 Thermowood Birch ThermoD | ★★★☆☆ |
| Structural / load-bearing | 🥇 Thermowood Birch ThermoD | ★★★☆☆ |
| Sauna / wet interiors | 🥇 Thermowood Birch ThermoD | ★★★★☆ |
Advantages & limitations
Thermowood Birch ThermoD
Advantages
- Rated for exterior exposure (EN 350 Class 2)
Limitations
- Few practical drawbacks within its intended uses
Thermowood Ash ThermoD
Advantages
- Rated for exterior exposure (EN 350 Class 2)
Limitations
- Few practical drawbacks within its intended uses
Recommendation
Choose Thermowood Birch ThermoD if…
- You want the stronger all-round engineering profile
Choose Thermowood Ash ThermoD if…
- You need the harder wear surface
- Its profile matches the application better than a single overall score
Frequently asked questions
Which is more durable, Thermowood Birch ThermoD or Thermowood Ash ThermoD?
Neither — both carry the same EN 350 rating (Class 2, Durable (treated)). For outdoor decisions between them, weigh dimensional stability and hardness instead.
Which wood is better for outdoor use?
They are closely matched outdoors — durability and stability come out almost level. Let the application decide: harder surface for decking traffic, lighter weight for cladding.
Is Thermowood Birch ThermoD harder than Thermowood Ash ThermoD?
No — Thermowood Ash ThermoD is harder (Janka 1320 vs 1210 lbf).
How we score. Each wood gets a weighted composite of the verified figures shown above: durability 22%, stability 18%, hardness 12%, bending strength 12%, machining ease 12%, stiffness 8%, flame spread 8%, lightness 8%. The Library Score is that composite's percentile rank within our 60-species library — 50 means the library median, 90 means it outperforms nine of every ten species we cover. No price data is scored — cost guidance is qualitative. The score summarises the data; it does not replace judgement about your specific application.