What is the standard increment for structural timber lengths?

Lengths typically start at 1.5 m and increase in standard increments of 0.3 m up to 6.0 m.

Do these dimensions apply to finished or rough sawn timber?

The dimensions represent rough sawn timber sizes. Machining, planning, or finishing requires appropriate dimensional allowances.

How does moisture affect the specified sizes?

Dimensions are standard at 12% moisture content (IS 287). Timber will shrink if dried below this level and swell if moisture increases.

IS 4891

: 1988

preferred cut sizes of structural timber - Specification

CurrentSpecializedSpecificationBIMStructural Engineering · Building Construction Practices incl. Painting, Varnishing

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This standard specifies the preferred dimensions (thickness, width, and length) for cut sizes of structural timber. It aims to facilitate standardization, reduce milling wastage, and optimize the availability of structural timber in the market.

preferred cut sizes of structural timber - Specification

Quick Reference Values

Minimum preferred length1.5 m

Maximum preferred length6.0 m

Length increments0.3 m

Moisture content for standard dimensions12 percent

Tolerance for width/thickness < 100mm+3 mm, -1 mm

Tolerance for width/thickness >= 100mm+6 mm, -2 mm

Practical Notes

Always specify timber dimensions at standard moisture content (typically 12%) as actual dimensions will vary with shrinkage or swelling.

Using standard preferred sizes drastically reduces material cost and lead time, as sawmills optimize their log cutting for these dimensions.

Specified sizes are for sawn timber. If planed or finished timber is required, nominal allowances (usually 2-3 mm per face) must be added during procurement.