cut sizes of timber
1971 Edition

The code defines nominal thickness and width sizes for cut timber categorized into groups such as batten, scantling, plank, and baulk, as per IS 707-1968. Preferred nominal dimensions are indicated in the standard’s designated table, facilitating uniformity in stocking. Typical thicknesses range from 12 mm for battens to over 75 mm for baulks, with corresponding widths specified accordingly.

For non-structural timber, the standard classifies material into Grade 1 and Grade 2 based on permissible defects. Grade 1 timber has stricter limitations on defects such as knots, checks, and slope of grain, whereas Grade 2 allows larger or more frequent defects. This grading ensures timber suitability for uses where structural integrity is less critical but appearance and durability are maintained.

Permissible defects include limits on slope of grain (1:15 for Grade 1 and 1:12 for Grade 2), maximum size and quantity of live knots, allowable check depths, end splits, pitch pockets, and various forms of warp such as bow, spring, twist, and cup. Grade 1 timber has tighter restrictions to minimize the effect on strength and appearance, while Grade 2 allows for greater defect size and frequency but still maintains usability.

The dimensions are standardized at 20% moisture content and adjustments are necessary for cross-sectional dimensions only, as lengthwise dimensions remain constant. For timber species with specific gravity under 0.6 or more stable species, a dimensional change of 0.2% per 1% moisture variation from 20% is applied. For less stable species with specific gravity 0.6 or above, a 0.3% change per 1% moisture difference is used. Formulas provided in the standard calculate adjusted dimensions accordingly.

Each piece of cut timber must be marked at one end indicating the size (thickness and width), intended application or end use, and the manufacturer’s name or trademark. Optionally, the ISI Certification Mark may be displayed to confirm compliance with Indian Standards. These markings ensure traceability, quality assurance, and proper identification throughout the timber supply chain.