EN 338:2016

Structural timber - Strength classes

This European Standard establishes a system of strength classes for general use in design codes.
It gives characteristic strength and stiffness properties and density values for each class to which EN 14081-1 refers.
This standard is applicable to all softwood and hardwood timber for structural use.

Bauholz für tragende Zwecke - Festigkeitsklassen

Diese Europäische Norm legt ein System von Festigkeitsklassen für den allgemeinen Gebrauch in Bemessungsnormen fest.
Sie gibt charakteristische Werte der Festigkeit, Steifigkeit und Rohdichte für jede Klasse an, auf die sich EN 14081 1 bezieht.
Diese Norm gilt für alle Nadel- und Laubhölzer für tragende Zwecke innerhalb des Anwendungsbereiches von EN 14081-1.

Bois de structure - Classes de résistance

La présente Norme européenne établit un système de classes de résistance d'utilisation générale pour les codes de calcul de structures.
Elle donne, pour chaque classe référencée dans l'EN 14081-1, les valeurs caractéristiques des propriétés de résistance et de rigidité, et les valeurs de masse volumique.
La présente norme s'applique à tous les bois résineux et feuillus à usage structurel.

Konstrukcijski les - Trdnostni razredi

Ta evropski standard določa sistem razredov trdnosti za splošno uporabo pri projektnih kodah.. Določa značilne lastnosti trdnosti in togosti ter vrednosti gostote za vsak razred, na katerega se sklicuje EN 14081-1. Ta standard se uporablja za vse mehke in trde vrste lesa za uporabo pri konstrukcijah.

General Information

• Status: Published
• Publication Date: 05-Apr-2016
• ICS: 79.040 - Wood, sawlogs and sawn timber
• Technical Committee: CEN/TC 124 - Timber structures
• Drafting Committee: CEN/TC 124/WG 2 - Solid timber
• Current Stage: 9093 - Decision to confirm - Review Enquiry
• Start Date: 17-Jul-2022
• Completion Date: 23-Sep-2025
• Ref Project: SIST EN 338:2016 - Structural timber - Strength classes

Relations

• Replaces: EN 338:2009 - Structural timber - Strength classes
• Effective Date: 08-Jun-2022

Overview - EN 338:2016 (Structural timber - Strength classes)

EN 338:2016, published by CEN and prepared by CEN/TC 124, establishes a harmonised system of strength classes for structural timber for use in European design codes. The standard defines characteristic strength, stiffness (modulus of elasticity) and density values for each class and applies to both softwood and hardwood intended for structural use. EN 338:2016 supersedes EN 338:2009 and links directly to grading and property determination procedures in EN 14081‑1 and EN 384.

Key topics and technical requirements

• Classification system:
  • Strength classes designated as Cxx (softwood, edgewise bending), Txx (softwood, tension-based) and Dxx (hardwood, edgewise bending). The numeric suffix indicates the 5‑percentile characteristic strength in N/mm².
• Characteristic properties provided:
  • Bending strength, tension/compression parallel and perpendicular to grain, shear strength, mean and 5‑percentile modulus of elasticity, and mean and 5‑percentile density for each class.
• Grading and allocation:
  • Populations (one species or species combination from one source) must have characteristic values determined per EN 384.
  • Visual grading must follow a grading standard meeting EN 14081‑1; machine grading must comply with EN 14081 (all parts).
  • A population can be assigned to a strength class only if its characteristic values equal or exceed the tabulated values in EN 338 (Tables 1–3).
• Special notes:
  • T‑classes are mainly intended for glued laminated timber (glulam) or other applications dominated by tension.
  • Values are given for timber at typical equilibrium moisture content (≈12%) and for timber without fissures (shear strength per EN 408).

Applications and who uses EN 338:2016

• Structural engineers and designers: to specify timber strength classes in load-bearing calculations and design documentation.
• Timber graders and manufacturers: to set visual or machine grading procedures and to certify batches against class values.
• Glulam and engineered timber producers: to select appropriate T‑classes where tension performance is critical.
• Regulators, certification bodies, and standards committees: to harmonise national standards and product conformity with European rules.
• Architects and contractors: for material selection when specifying load-bearing timber members.

Related standards

• EN 14081 (all parts) - Strength graded structural timber (visual and machine grading)
• EN 14081‑1 - Requirements for visual grading standards
• EN 384 - Determination of characteristic values of mechanical properties and density
• EN 408 - Structural timber - Test methods (relevant to shear and bending tests)

EN 338:2016 is essential for consistent specification, grading and interchangeability of structural timber across Europe, improving design confidence and enabling reliable use of both softwood and hardwood in construction.

Standards Content (Sample)

SLOVENSKI STANDARD
01-junij-2016
1DGRPHãþD
SIST EN 338:2010
Konstrukcijski les - Trdnostni razredi
Structural timber - Strength classes
Bauholz für tragende Zwecke - Festigkeitsklassen
Bois de structure - Classes de résistance
Ta slovenski standard je istoveten z: EN 338:2016
ICS:
79.040 Les, hlodovina in žagan les Wood, sawlogs and sawn
timber
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN 338
EUROPEAN STANDARD
NORME EUROPÉENNE
April 2016
EUROPÄISCHE NORM
ICS 79.040 Supersedes EN 338:2009
English Version
Structural timber - Strength classes
Bois de structure - Classes de résistance Bauholz für tragende Zwecke - Festigkeitsklassen
This European Standard was approved by CEN on 30 January 2016.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2016 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 338:2016 E
worldwide for CEN national Members.

Content
Page
European foreword . 3
Introduction . 4
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Symbols and abbreviations . 5
5 Classification of structural timber . 6
6 Allocation of a population to a strength class . 10
6.1 Grading . 10
6.1.1 Visual graded timber . 10
6.1.2 Machine graded timber . 10
6.2 Classification . 10
6.2.1 Characteristic values . 10
6.2.2 Allocation to a strength class . 10
Bibliography . 11

European foreword
This document (EN 338:2016) has been prepared by Technical Committee CEN/TC 124 “Timber structures”,
the secretariat of which is held by AFNOR.
This European Standard shall be given the status of a national standard, either by publication of an identical
text or by endorsement, at the latest by October 2016, and conflicting national standards shall be withdrawn
at the latest by October 2016.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN 338:2009.
Compared to EN 338:2009, the following modifications have been made:
— new table of strength classes for softwood species based on tension tests;
— extension with new classes in the table of strength classes for hardwood species based on edgewise
bending tests;
— modification of some characteristic values for strength, stiffness and density;
— equations to determine the characteristic values of other strength properties from the grade
determining properties has been transferred to EN 384.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech
Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece,
Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland,
Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom.
Introduction
A strength class system groups together grades, species and sources with similar strength properties thus
making them interchangeable. This then permits an engineer to specify a chosen strength class and use the
characteristic strength values of that class in design calculations.
1 Scope
This European Standard establishes a system of strength classes for general use in design codes.
It gives characteristic strength and stiffness properties and density values for each class to which
EN 14081-1 refers.
This standard is applicable to all softwood and hardwood timber for structural use, within the scope of
EN 14081-1.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
EN 384, Structural timber — Determination of characteristic values of mechanical properties and density
EN 14081 (all parts), Timber structures — Strength graded structural timber with rectangular cross section
3 Terms and definitions
For the purposes of this document, the following term and definition apply.
3.1
population
timber of one species or species combination and one source for which the strength, stiffness and density
properties apply
4 Symbols and abbreviations
E
m,0,mean mean characteristic value of modulus of elasticity in bending parallel to grain (in
kN/mm );
E mean characteristic value of modulus of elasticity in tension parallel to grain (in
t,0,mean
kN/mm );
E 5-percentile characteristic value of modulus of elasticity in bending parallel to
m,0,k
grain (in kN/mm );
E 5-percentile characteristic value of modulus of elasticity in tension parallel to
t,0,k
grain (in kN/mm );
E mean characteristic value of modulus of elasticity in bending perpendicular to
m,90,mean
grain (in kN/mm );
E mean characteristic value of modulus of elasticity in tension perpendicular to
t,90,mean
grain (in kN/mm );
f 5-percentile characteristic value of compressive strength parallel to grain (in
c,0,k
N/mm );
f 5-percentile characteristic value of compressive strength perpendicular to grain
c,90,k
(in N/mm );
f 5-percentile characteristic value of bending strength (in N/mm );
m,k
f 5-percentile characteristic value of tensile strength parallel to grain (in N/mm );
t,0,k
f 5-percentile characteristic value of tensile strength perpendicular to grain (in
t,90,k
N/mm );
f 5-percentile characteristic value of shear strength (in N/mm );
v,k
G mean characteristic value of shear modulus (in kN/mm );
mean
ρ 5-percentile characteristic value of density (in kg/m );
k
ρ mean characteristic value of density (in kg/m )
mean
5 Classification of structural timber
This standard provides for a number of strength classes, each designated by a number indicating the value of
the edgewise bending or tension strength in N/mm .
For softwood species based on edgewise bending tests, the characteristic values of strength, stiffness and
density for
...