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IS 6534:1971 is the Indian Standard (BIS) for guiding principles for grading and inspection of timber. This standard lays down the guiding principles for the grading and inspection of timber. It defines common defects and establishes a framework for creating specific grading rules based on the intended end-use of the wood.
Guiding principles for grading and inspection of timber
BIM-relevant code. See the BIM Hub for ISO 19650, IFC, and LOD/LOIN frameworks used alongside it.
Practical Notes
! This is a foundational document; it provides the principles for creating grading rules, not the specific rules for a particular timber species (which are in other standards).
! The standard emphasizes visual inspection, so understanding how to identify and measure defects like knots, slope of grain, and checks is critical.
! Grading is essential for determining the suitability of timber for structural versus non-structural (joinery, furniture) applications.
EN 14081-1:2016+A1:2019CEN (European Committee for Standardization), Europe
HighCurrent
Timber structures — Strength graded structural timber with rectangular cross section — Part 1: General requirements
Defines the framework and requirements for both visual and machine strength grading of structural timber in Europe.
ASTM D245 - 20 (2024)ASTM International, USA
HighCurrent
Standard Practice for Establishing Structural Grades and Related Allowable Properties for Visually Graded Lumber
Provides the base principles for developing visual grading rules and assigning strength properties to those grades.
BS 4978:2007+A2:2017BSI (British Standards Institution), UK
MediumCurrent
Visual strength grading of softwood — Specification
Provides specific visual grading rules for softwood species, defining defect limits for grades like SS and GS.
ISO 19131:2018ISO (International Organization for Standardization), International
HighCurrent
Structural timber — Visual strength grading
Specifies requirements for visual strength grading of structural timber, serving as a global baseline.
Key Differences
≠IS 6534 provides descriptive quality grades (1, 2, 3) without assigning specific structural properties. Modern standards like EN 14081-1 link visual grades to pre-defined strength classes (e.g., C16, C24) with established engineering values.
≠The Indian standard is a general guide for numerous species, whereas international standards are often part of a system with specific rules for different species or species groups (e.g., softwoods vs. hardwoods, or specific regional species).
≠IS 6534 is from 1971 and does not cover modern grading concepts like machine strength grading, which is a key component of frameworks like EN 14081-1.
≠Measurement techniques differ. For example, European standards (e.g., BS 4978) use the Knot Area Ratio (KAR) for a more precise assessment of knot impact, while IS 6534 uses simpler measurements of knot diameter relative to face width.
Key Similarities
≈All standards are based on the same fundamental principle: visual defects reduce timber strength, and limiting them allows sorting into quality or strength grades.
≈The primary strength-reducing characteristics considered are universal: knots, slope of grain, shakes, checks, splits, and wane.
≈All standards establish multiple grade levels (e.g., Grade 1/2/3 in IS 6534; SS/GS in BS 4978) to enable efficient use of timber by matching quality to application requirements.
≈The basic method of measuring the slope of grain as a ratio (e.g., 1 in 12) is a common concept across all the standards.
Parameter Comparison
Parameter
IS Value
International
Source
Number of Structural Grades (Cut Timber)
3 grades (Grade 1, Grade 2, Grade 3)
2 primary grades (SS - Special Structural, GS - General Structural)
BS 4978:2007+A2:2017
Slope of Grain Limit (Highest Grade)
Not steeper than 1 in 15
Not steeper than 1 in 10
BS 4978:2007+A2:2017 (SS Grade)
Slope of Grain Limit (Second Grade)
Not steeper than 1 in 12
Not steeper than 1 in 6
BS 4978:2007+A2:2017 (GS Grade)
Wane Limit (Highest Grade)
Permitted up to 1/8 of the width of face or edge.
Permitted up to 1/3 of the width of face or edge.
BS 4978:2007+A2:2017 (SS Grade)
Knot Size Limit (Highest Grade, Margin Knot)
Not to exceed 1/4 of the width of the face.
Not to exceed 1/3 of the width of the edge.
BS 4978:2007+A2:2017 (SS Grade)
Through Checks/Shakes (Highest Grade)
Not permissible.
Not permitted. Other fissures are limited in length and depth.
BS 4978:2007+A2:2017 (SS Grade)
⚠ Verify details from original standards before use
Key Values0
No quick reference values available for this code yet.
Tables & Referenced Sections
Key Tables
No tables data
Key Clauses
Clause 3 - Defects in Timber
Clause 4 - Principles for Formulation of Grading Rules
To provide a uniform and systematic basis for grading and inspecting timber based on its natural defects and characteristics (Clause 1.1).
Does this standard give specific allowable knot sizes for grading?+
No, it outlines the principles for how to set those limits, but does not provide the specific values. These are found in standards for specific timber products or species.
What are the main types of defects considered for grading?+
Defects include knots, cross grain, checks, splits, shakes, insect attack, decay, and warp, among others (Clause 3).
What is 'cutting' in the context of timber grading?+
A hypothetical rectangular portion of a piece of timber, free from defects, used to assess the grade of the timber piece (Clause 2.3).