SIST EN 336:2013

Overview

SIST EN 336:2013 is a European standard developed by CEN that specifies the sizes and allowable deviations for structural timber. It applies to both softwood and hardwood species used in construction and structural applications. The standard defines target sizes at a reference moisture content of 20% and details two tolerance classes for permitted dimensional deviations. It covers sawn and prepared square-edged structural timber with thicknesses or widths greater than 6 mm.

This specification ensures uniformity and quality in structural timber dimensions, facilitating interoperability and reliability in timber engineering and construction projects across Europe.

Key Topics

• Scope and Applicability
  SIST EN 336:2013 applies to structural timber with parallel edges used in load-bearing applications, including timber sections thicker than 6 mm. It is relevant for both softwood and hardwood species.

• Target Size and Moisture Content
  Dimensions are specified based on a reference moisture content of 20%. The standard provides guidelines on how timber size changes with moisture content variations:

  • Softwoods and poplar: thickness and width increase or decrease by 0.25% per 1% change in moisture content from 20% (up to 30%).
  • Hardwoods: thickness and width change by 0.35% per 1% moisture content change.

• Permitted Deviations
  Two tolerance classes define permitted deviations from target sizes:

  • Tolerance Class 1 (wider tolerances for general applications):
    • Thickness/width ≤ 100 mm: -1 mm / +3 mm
    • 100 < thickness/width ≤ 300 mm: -2 mm / +4 mm
    • Thickness/width > 300 mm: -3 mm / +5 mm
  • Tolerance Class 2 (narrower tolerances for precise applications):
    • Thickness/width ≤ 100 mm: -1 mm / +1 mm
    • 100 < thickness/width ≤ 300 mm: -1.5 mm / +1.5 mm
    • Thickness/width > 300 mm: -2 mm / +2 mm

• Measurement Standards
  Dimensions should be measured following EN 1309-1, and moisture content determined using EN 13183 parts 1, 2, or 3, ensuring consistency in assessment methods.

• Length Deviations
  Negative length deviations (shorter than target length) are not allowed. Overlengths should be controlled via contractual agreements.

Applications

SIST EN 336:2013 is essential in multiple practical fields involving structural timber, including:

• Construction Engineering
  Ensures timber components meet strict dimensional accuracy for load-bearing elements, supporting structural integrity and safety.

• Timber Manufacturing
  Provides standardized size tolerances for sawn and prepared timber products enabling quality control and conformity across manufacturers.

• Quality Assurance and Inspection
  Assists inspectors and engineers in verifying timber sizes against established tolerances, factoring in moisture-induced size changes for accurate assessment.

• Architectural Design
  Facilitates the design of timber structures with predictable, reliable component dimensions, supporting modular construction and material optimization.

• Timber Trade and Procurement
  Enables clear communication of size expectations and tolerances between suppliers and buyers, reducing disputes and enhancing supply chain efficiency.

Related Standards

• EN 1309-1 – Method of measurement of dimensions for sawn timber, guiding accurate size measurement techniques.
• EN 13183 (Parts 1, 2, 3) – Standards for moisture content determination by oven dry, electrical resistance, and capacitance methods.
• EN 14298 – Sawn timber drying quality assessment, relevant for understanding and controlling moisture-related changes.
• EN 1995 (Eurocode 5) – Design of timber structures, where SIST EN 336:2013 ensures compliance of materials used.

By adhering to SIST EN 336:2013, stakeholders throughout the timber construction value chain can ensure structural timber components meet consistent size specifications with reliable quality, supporting safer, more efficient, and standardized timber engineering practices across Europe.