Structural timber is the collective term for construction-grade wood in beam form — rectangular or square cross-section — used as a load-bearing element in floors, roofs, canopies and other structures. It differs from plank material by its larger cross-section and structural use.
Common dimensions
| Dimension (mm) | Application |
|---|---|
| 50 x 100 | Light battens, supporting |
| 50 x 150 | Rafters, deck joists |
| 63 x 175 | Rafters, purlins (medium) |
| 75 x 200 | Purlins, beams |
| 75 x 225 | Heavy beams, spans up to 5 m |
| 100 x 100 | Posts, columns |
| 120 x 120 | Heavy posts |
| 150 x 150 | Structural columns |
Wood species
- Spruce — Standard structural timber, inexpensive, indoor or sheltered outdoor use
- Douglas fir — More durable, suitable for exposed outdoor use
- Pressure-treated spruce — Budget option for outdoor use
- Larch — Comparable to Douglas fir
Planed vs. rough-sawn
- Rough-sawn — Straight from the saw, rough surface. Cheaper. The stated dimension is the actual dimension.
- Planed — Smooth planed surface. The actual dimension is 3-5 mm smaller than the stated dimension (wood has been planed off).
Example: a “75 x 200 planed” beam is actually approximately 70 x 195 mm.
Related terms
- Beam
- Girder
- Purlins
- Spruce wood
- Douglas fir wood
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