The timber extracted from felled trees is classified based on the position of the trees as per IS 399 belongs to:
IS 399: Classification of Timber
Indian Standard IS 399 provides a systematic way to classify timber based on various criteria to ensure clarity in trade and usage. The main bases for classification are position, modulus of elasticity, and durability.
Based on Position:
- Standing timber: A living tree before it has been felled.
- Rough timber: A felled tree before it has been processed into logs or planks.
- Converted timber: Timber that has been sawn into pieces like logs, planks, posts, etc.
Based on Modulus of Elasticity (E):
- Group A: E > 12.5 kN/mm² (High stiffness)
- Group B: E = 9.8 – 12.5 kN/mm² (Medium stiffness)
- Group C: E = 5.6 – 9.8 kN/mm² (Low stiffness)
Based on Durability (Average Life):
- High Durability: Average life of 10 years or more.
- Medium Durability: Average life between 5 and 10 years.
- Low Durability: Average life less than 5 years.
đź“ť Detailed Analysis of the Options
(a) Living timber & (d) Standing timber
Standing timber is the correct term used in IS 399 to refer to a living tree before it has been felled. "Living timber" is a descriptive phrase but not the official classification. Both refer to a tree that has not yet been cut down.
(c) Dead timber
This term is not a formal classification based on position in IS 399. While a tree can be dead, the standard classifies timber based on whether it is standing or has been felled and processed.
(b) Rough timber
This is the correct answer. According to IS 399, once a tree is felled (cut down), the resulting log is referred to as rough timber. It is the raw material, with bark still on, before any further cutting or shaping into planks, posts, or beams.
đź“Š Summary of IS 399 Timber Classifications
| Basis | Classification | Description |
|---|---|---|
| Position | Standing Timber | A living tree. |
| Rough Timber | A felled tree (log). | |
| Converted Timber | Sawn timber (planks, posts, etc.). | |
| Modulus of Elasticity | Group A | E > 12.5 kN/mm² |
| Group B | E = 9.8 – 12.5 kN/mm² | |
| Group C | E = 5.6 – 9.8 kN/mm² | |
| Durability | High | Average life ≥ 10 years |
| Medium | 5 ≤ Average life < 10 years | |
| Low | Average life < 5 years |
đź’ˇ Study Tips
- Follow the Process: Think of the timber's journey. It starts as Standing (living), then becomes Rough (felled log), and finally gets Converted (sawn into pieces).
- Rough = Raw: Associate "rough timber" with the raw, unprocessed log immediately after felling.
- Check the Standard: Remember that these specific terms (Standing, Rough, Converted, Groups A/B/C, etc.) come directly from IS 399.