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 In Translation
Public Enquiry End Date
10-Nov-2013
Publication Date
19-May-2016
ICS
79.040 - Wood, sawlogs and sawn timber
Technical Committee
KON.005 - Timber structures
Current Stage
6100 - Translation of adopted SIST standards (Adopted Project)
Start Date
17-Jun-2025
Due Date
16-Jun-2026
Ref Project
EN 338:2016 - Structural timber - Strength classes

Relations

Replaces
SIST EN 338:2010 - Structural timber - Strength classes
Effective Date
01-Jun-2016

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.

Frequently Asked Questions

SIST EN 338:2016 is a standard published by the Slovenian Institute for Standardization (SIST). Its full title is "Structural timber - Strength classes". This standard covers: 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.

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.

SIST EN 338:2016 is classified under the following ICS (International Classification for Standards) categories: 79.040 - Wood, sawlogs and sawn timber. The ICS classification helps identify the subject area and facilitates finding related standards.

SIST EN 338:2016 has the following relationships with other standards: It is inter standard links to SIST EN 338:2010. Understanding these relationships helps ensure you are using the most current and applicable version of the standard.

You can purchase SIST EN 338:2016 directly from iTeh Standards. The document is available in PDF format and is delivered instantly after payment. Add the standard to your cart and complete the secure checkout process. iTeh Standards is an authorized distributor of SIST standards.

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
...

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The SIST EN 338:2016 standard provides a comprehensive framework for the classification of structural timber into strength classes, which is critical for ensuring the integrity and safety of timber-based structures. The scope of this European Standard is well-defined, establishing a systematic approach for categorizing both softwood and hardwood timbers based on their characteristic strength and stiffness properties, as well as density values. This classification is particularly relevant for engineers and architects, as it facilitates the appropriate selection of materials for structural applications. One of the key strengths of the SIST EN 338:2016 standard lies in its detailed specifications, which align with the requirements set forth in EN 14081-1. These specifications enable designers to make informed decisions regarding material selection, thereby enhancing the structural performance and safety of timber constructions. The inclusion of comprehensive characteristic values for various strength classes ensures a systematic approach to timber design, promoting reliability and consistency across the structural engineering field. Additionally, the standard's relevance in modern engineering cannot be overstated. With the growing emphasis on sustainable construction practices, the use of timber has become increasingly prominent. By establishing clear strength classes, SIST EN 338:2016 effectively supports the ongoing trend towards using renewable materials while maintaining adherence to safety standards in construction. The standard not only aids in compliance with regulatory requirements but also bolsters confidence among stakeholders in the construction industry regarding the quality and reliability of timber products. Overall, SIST EN 338:2016 plays an essential role in the field of structural timber design, equipping professionals with the necessary tools to classify and utilize timber effectively in construction projects. Its rigorous approach to defining strength classes underscores its importance in ensuring the safety and performance of structures that utilize timber as a primary material.

SIST EN 338:2016は、構造用木材の強度クラスを定義する欧州標準であり、設計コードにおける一般的な使用のための強度クラスシステムを確立しています。この標準は、EN 14081-1に関連する各クラスの特性強度、剛性特性、および密度値を提供しています。 この標準の強みは、全ての軟材および硬材に適用できる点であり、構造用木材の設計において一貫性を持たせることができます。具体的には、開発された強度クラスは、木材の性能を明確に示し、設計者が適切な材料を選定する際の確固たる基準となります。また、標準により木材の使用条件や要求される特性が明文化されているため、施工時の信頼性や安全性が向上します。 SIST EN 338:2016は、特に建築分野において必要不可欠な文書であり、品質管理と性能の評価においても高い関連性を持っています。建設業界の専門家にとって、この標準を参照することで、木材の使用に関する理解を深め、標準化された強度データに基づいた設計を行うことが可能となります。このように、SIST EN 338:2016は、構造用木材の強度クラスに関して、技術的な基盤を提供するだけでなく、持続可能な建築の実現に向けた重要な指標でもあります。

La norme SIST EN 338:2016 est un document fondamental qui établit un système de classes de résistance pour le bois utilisé dans les structures. Son champ d'application est essentiel car il couvre tant les bois résineux que les bois feuillus destinés à un usage structural, offrant ainsi une vaste portée d'application dans le secteur de l'ingénierie et de la construction. Parmi les forces de cette norme, on trouve la définition claire des propriétés caractéristiques de résistance et de rigidité, ainsi que des valeurs de densité pour chaque classe de bois. Cela permet aux concepteurs et aux ingénieurs de sélectionner judicieusement les matériaux en fonction des exigences spécifiques des projets. L'importance de cette normalisation se manifeste également dans la manière dont elle facilite l'harmonisation des codes de conception à travers l'Europe, encourageant ainsi un échange fiable et standardisé des informations sur le bois. La pertinence de la norme SIST EN 338:2016 réside dans sa capacité à répondre aux besoins contemporains du secteur du bâtiment en matière de sécurité et de performance. En fournissant des données précises sur les classes de résistance, elle contribue à la durabilité et à la fiabilité des constructions en bois, ce qui est crucial à une époque où l'efficacité énergétique et la durabilité des matériaux sont au centre des préoccupations environnementales et économiques. En somme, la norme SIST EN 338:2016 s'impose comme un document incontournable pour quiconque travaille dans le domaine du bois structurel, en offrant un cadre normatif qui aide à garantir la qualité et la sécurité des constructions.

Die SIST EN 338:2016 ist ein wesentlicher Standard, der ein System von Festigkeitsklassen für die allgemeine Anwendung in Entwurfscodes festlegt. Dieser Standard bietet eine umfassende Übersicht über die charakteristischen Festigkeits- und Steifigkeitsmerkmale sowie die Dichtewerte für jede Klasse, auf die in der EN 14081-1 verwiesen wird. Ein entscheidender Punkt des Dokuments ist seine breite Anwendbarkeit. Die Festigkeitsklassen sind für alle Nadelhölzer und Laubhölzer, die im Bauwesen verwendet werden, relevant. Dies gewährleistet, dass der Standard eine große Palette von Holzarten abdeckt und es den Planern und Ingenieuren ermöglicht, fundierte Entscheidungen bei der Materialauswahl zu treffen. Ein weiterer großer Vorteil von SIST EN 338:2016 besteht in der Schaffung eines einheitlichen Rahmens, der die Kommunikation zwischen den Akteuren der Baubranche erleichtert. Durch die klar definierten Festigkeits- und Steifigkeitswerte fördert dieser Standard die Sicherheit und Effizienz im Bauwesen. Zudem ermöglicht die Standardisierung eine bessere Vergleichbarkeit von Materialien und deren Eigenschaften, was sowohl für Hersteller als auch für Verbraucher von Bedeutung ist. Die Relevanz dieser Norm ist nicht zu unterschätzen, da sie wesentliche Grundlagen für die Berechnung und den Entwurf von Tragwerken bereitstellt. Indem sie eine systematische Klassifizierung von Holz als Baumaterial vorlegt, trägt die SIST EN 338:2016 dazu bei, die Qualität und Langlebigkeit von Holzstrukturen zu optimieren und die Anforderungen an Nachhaltigkeit zu unterstützen. Zusammenfassend lässt sich sagen, dass die SIST EN 338:2016 ein robustes und flexibles Instrument bereitstellt, das die Festigkeitsklassen von Strukturholz klar definiert und somit für die Anwendung in der Bauindustrie unverzichtbar ist.

SIST EN 338:2016은 구조용 목재의 강도 등급을 규정하는 유럽 표준으로, 설계 코드에서 일반적으로 사용되는 강도 등급 시스템을 설립합니다. 이 표준은 각 강도 등급에 대해 특성 강도, 강성 특성 및 밀도 값을 제시하며, EN 14081-1과 연관이 있습니다. SIST EN 338:2016의 범위는 구조적 용도로 사용되는 모든 침엽수와 활엽수 목재에 적용됩니다. 이는 다양한 목재 종류에 대한 적합성을 보장하여 설계 시 목재 선택의 폭을 넓히는 데 큰 기여를 합니다. 강점으로는, 이 표준이 제공하는 강도와 강성 특성이 명확하게 정의되어 있어, 엔지니어와 설계자가 보다 신뢰성 있는 구조를 설계할 수 있도록 돕습니다. 기준에 따른 특성값은 구조 안전성 및 내구성을 높이는 데 있어 결정적인 역할을 수행합니다. 또한, 다양한 목재 재료에 대한 포괄적인 데이터는 사용자가 보다 효과적으로 자재를 비교하고 선택할 수 있게 해 줍니다. 따라서, SIST EN 338:2016은 구조용 목재의 설계와 적용에 있어 필수적인 문서로, 최신 건축 기준을 충족하는 것을 목표로 하는 모든 전문가에게 매우 중요한 표준입니다. 이 표준은 특히 유럽 지역 내에서의 목재 사용 및 관리에 있어 중요한 기준점 역할을 하며, 지속 가능한 건축물 설계에 기여하는 바가 큽니다.