oSIST prEN 460:2019

SLOVENSKI STANDARD
oSIST prEN 460:2019
01-januar-2019
Trajnost lesa in lesnih izdelkov - Naravna trajnost masivnega lesa - Zahteve po
trajnosti lesa, ki se uporablja v posameznih razredih ogroženosti
Durability of wood and wood-based products - Natural durability of solid wood - Guide to
the durability requirements for wood to be used in hazard classes
Dauerhaftigkeit von Holz und Holzprodukten - Natürliche Dauerhaftigkeit von Vollholz -
Leitfaden für die Anforderungen an die Dauerhaftigkeit von Holz für die Anwendung in
den Gebrauchsklassen
Durabilité du bois et des matériaux dérivés du bois - Durabilité naturelle du bois massif -
Guide d'exigences de durabilité du bois pour son utilisation selon les classes de risque
Ta slovenski standard je istoveten z: prEN 460
ICS:
79.040 Les, hlodovina in žagan les Wood, sawlogs and sawn
timber
oSIST prEN 460:2019 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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oSIST prEN 460:2019

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oSIST prEN 460:2019


DRAFT
EUROPEAN STANDARD
prEN 460
NORME EUROPÉENNE

EUROPÄISCHE NORM

November 2018
ICS 79.040 Will supersede EN 460:1994
English Version

Durability of wood and wood-based products - Natural
durability of solid wood - Guide to the durability
requirements for wood to be used in hazard classes
Durabilité du bois et des matériaux dérivés du bois - Dauerhaftigkeit von Holz und Holzprodukten -
Durabilité naturelle du bois massif - Guide d'exigences Natürliche Dauerhaftigkeit von Vollholz - Leitfaden für
de durabilité du bois pour son utilisation selon les die Anforderungen an die Dauerhaftigkeit von Holz für
classes de risque die Anwendung in den Gebrauchsklassen
This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee
CEN/TC 38.

If this draft becomes a European Standard, 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.

This draft European Standard was established by CEN 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, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and United Kingdom.

Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are
aware and to provide supporting documentation.

Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without
notice and shall not be referred to as a European Standard.


EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2018 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 460:2018 E
worldwide for CEN national Members.

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Contents Page
European foreword . 3
Introduction . 4
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Use class . 7
5 Durability classes . 7
6 Consequence of failure . 8
7 Material resistance in the various Use classes . 8
7.1 General . 8
7.2 Durability: wood-destroying fungi . 8
7.3 Durability: wood-destroying beetles . 11
7.4 Durability: termites . 11
7.5 Durability: marine organisms . 11
Annex A (informative) Important factors in the relationship between expected service life
and natural durability . 12
A.1 Service life . 12
Annex B (informative) Example of a factorisation approach for durability-based design and
service life prediction of timber structures . 13
Annex C (informative) Moisture dynamics . 16
C.1 General . 16
C.2 Treatability . 16
C.3 Moisture dynamics . 16
C.4 Test methods . 16
Annex D (informative) National interpretation of performance classes . 18
Annex E (informative) Consequence of Failure (CoF) . 19
Bibliography . 21

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European foreword
This document (prEN 460:2018) has been prepared by Technical Committee CEN/TC 38 “Durability of
wood and wood-based products”, the secretariat of which is held by AFNOR.
This document is currently submitted to the CEN Enquiry.
This document will supersede EN 460:1994.
Compared to the current EN 460, the following modifications apply:
— general modifications.

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Introduction
There is increasing need to understand and be able to communicate with users the service life of wooden
components, especially in construction. Service life in the Construction Products Regulations is
performance within an economically acceptable period, under normal exposure and normal
maintenance. It is usually considered to be how many years a construction component will provide
satisfactory function in its use environment. This standard is concerned with performance classification
for wood and wood-based products, the first building block for understanding service life for
construction products and other wood products.
Architects, construction engineers, the public, life cycle assessments (EN 15804) and other standards
(e.g. ISO 15686 series) require information on service life of construction products. Internationally wood
experts are currently developing methods and techniques to match data on durability of wood against
biological hazards with service life expectation, considering numerous influencing factors. As long as
reliable methods continue to be unavailable to prevent misleading interpretation of durability data and
to avoid unjustified expectations of service life the following is stated:
As for other materials wood in outdoor applications or exposed to high moisture content will age in a
distinct manner.
Wood utilized in the correct way can be in service for hundreds of years, as examples worldwide show.
At present due to the variety of conditions under which wood may be in service a direct, simple and
reliable deduction from durability classes to service life under real-use conditions is not available.
In addition to the durability against biological hazards service life depends on wood species, construction
details, climate, maintenance and many other issues.
The shorter the forecasting horizon the higher the probability that an estimated service life will be
reached in practice.
If wood-destroying organisms are likely to attack wood in service, a suitable pathway for meeting service
life needs to be selected. There are principally two pathways (i) by durability - either select a wood
species of sufficient natural durability or ensure the durability characteristics of the wood are enhanced
by treatment with a wood preservative, chemical modification or non-biocidal treatment to manage the
challenge presented in the use environment or (ii) by design for durability - minimizing the moisture risk
(or exposure dose) the wooden component is exposed to or by denying the access for organisms through
construction measures. Typically it is a combination of both to deliver a reasonable service life.
This standard allows a user to choose a wood or wood-based material for a product and knowing its
durability class alongside the use class of the end use environment establish a performance classification.
No attempt has been made to quantify the working life that could be expected from a particular
combination which is reflected in national interpretation documents (Annex D).
This standard includes scope for benchmark performance testing e.g. if the product performs better or
equal to the existing product in service, which can be used for CE marking purposes.

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1 Scope
This document gives guidance on the selection of wood species based on their biological durability and
selection of wood materials based on their specific enhanced resistance (wood preservative treatment,
wood modification and other non-biocidal methods) to attack by wood-destroying organisms for use as
solid wood, as engineered wood products (e.g. glulam) and as wood based composites (e.g. plywood,
wood polymer composites) in the use classes defined in EN 335.
This standard does not consider:
i) the durability characteristics of the glue used in engineered wood products or wood-based
composites;
ii) the aesthetic function of wood products (discoloration, surface weathering, mould);
iii) the strategy for protection of products as it will be different based on priorities of the user and client
and the type of product e.g. glulam compared to plywood.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
EN 335:2013, Durability of wood and wood-based products — Use classes: definitions, application to solid
wood and wood-based products
EN 350, Durability of wood and wood-based products — Testing and classification of the durability to
biological agents of wood and wood-based materials
CEN/TS 16818, Durability of wood and wood-based products — Moisture dynamics of wood and wood-
based products
EN 599-1, Durability of wood and wood-based products — Efficacy of preventive wood preservatives as
determined by biological tests — Part 1: Specification according to use class
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http://www.electropedia.org/
— ISO Online browsing platform: available at http://www.iso.org/obp
3.1
benchmark performance
performance of an existing product well-known in the market place in that end use
3.2
biological durability
quality of resistance against wood destroying organisms
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Note 1 to entry: This inherent resistance is due to the presence of natural components that can exhibit different
levels of toxicity towards biological organisms and/or to anatomical particularities or a specific constitution of
certain wood-based materials.
3.3
component
product manufactured as a distinct unit to serve a specific function or functions
3.4
consequence of failure (COF)
significance of the components failure in service expressed as a risk and a tolerance of that risk
3.5
critical biological hazard (CBH)
biological hazard or hazards that are most significant for the end use application and its geographical
location (see Annex E)
3.6
desired service life
how long a consumer requires a product to function
Note 1 to entry: National variation are refered in Annex D.
3.7
design life (DL)
service life intended by the designer as support to the client to enable specification decisions
3.8
estimated service life (ESL)
service life that a building or parts of a building would be expected to have in a set of specific in-use
conditions, determined from the reference service life data, having taken into account any differences
from the reference in-use conditions
3.9
exposure dose
scale which respresents the extent to which the product is challenged by moisture, temperature and
organisms as a result of climate and design
3.10
limit state
point where a product is deemed to have failed
Note 1 to entry: The limit state is reached earlier than loss of function (failure) occurs.
Note 2 to entry: For Use Class 3 models this is the on-set of decay.
3.11
material resistance
intrinsic ability of a material to endure a specific biological challenge
3.12
material resistance dose
scale that represents a combination of inherent durability and its moisture dynamic behaviour relevant
for the different biological agents
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3.13
moisture dynamics
physical characteristic of a wood species or wood product to respond to environmental conditions and
take on and release moisture (vapour or liquid)
3.14
performance class
scale to enable classification of broad performance outcome as short, medium or long
3.15
performance level
behaviour of the product in terms of its effectiveness in service defined as a combination of exposure
dose and material resistance dose
3.16
permeability to water
ease with which water penetrates a wood-based matrix (wood of a particular species, wood-based
material) and is released by evaporation
3.17
reference service life (RSL)
service life of a product, component, assembly or system which is known to be expected under a
particular set of in-use conditions which can form the basis for estimating the service life under other in-
use conditions
3.18
service life
period of time after installation during which a component part meets or exceeds the performance
requirements due to the amount of deterioration that can be tolerated before the component fails
3.19
wood modification
process of a chemical, biological or physical change of wood resulting in a permanent desired property
enhancement to primarily enhance biological durability and dimensional stability e.g. thermal
modification and acetylation
Note 1 to entry: The mode of modification action should be nonbiocidal.
4 Use class
The service situations in which wood is susceptible to biological attack have been divided into five Use
classes which are defined in EN 335. Guidance on the application of these use classes to solid wood is
given in EN 335. The required efficacy of preventive wood preservatives according to Use classes are
specified in EN 599-1.
5 Durability classes
Classification systems for the durability of solid wood and wood-based materials on resistance to attack
by various wood-destroying organisms are given in EN 350.
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6 Consequence of failure
This is an important element to plan the service life of wooden components. The higher the consequences
of failure the more conservative measures have to be taken to secure the performance targets. The
consequence of failure of structural elements is the highest as a life safety issue, the consequence of
failure of a cladding board is lower concerning life safety. Further targets are in the Construction Product
Regulations (CPR) which lists seven essential basic requirements for construction works. CoF often
considers life safety and ease of maintenance or replacement (Annex D).
If CoF are unacceptable then higher material resistance or techniques to reduce exposure dose need to
be selected. Although different components can fall into the same Use class, the likelihood of failure or
the consequence of failure can be quite different and these should be assessed in accordance with a
recognized process. Each component should be classified based on the likelihood and the severity of the
consequences of failure.
7 Material resistance in the various Use classes
7.1 General
The natural durability of a wood species should be considered separately for each wood-destroying
organism. In practice supplies of sawn timber may include sapwood as well as heartwood. If the
proportion of sapwood present is such that its loss would have adverse implications for the performance
of the component, or if the sapwood and heartwood cannot be distinguished, the durability of the whole
component should be regarded as equivalent to that of the sapwood.
In addition to the natural durability, there are other factors that influence performance (chemical and
physical) which should also be taken into consideration in the selection of a wood species and the
decision whether or not its durability requires enhancement to meet a desired service life.
In Use Class 3 the significance of moisture dynamics is of most influence compared with other Use Class
aplications. Wood with low permeability may acquire lower moisture contents under intermittent
wetting conditions, compared to a more permeable species, and will therefore have a reduced risk of
fungal attack under such service conditions.
Moisture has a significant influence on the mechanical and physical properties and on the biological
durability of wood and wood-based products. For example, the test method described in the European
Technical Specification CEN/TS 16818 provides a basis for assessment of the moisture dynamics of wood
and wood-based products in service. The method permits the determination of the water uptake and
moisture release which may provide important information on the susceptibility to the onset of fungal
attack in certain end uses.
Information on some further factors is given in Annex A.
For each product application, the performance against biological agents needs to be considered, and the
critical biological hazard needs to be identified.
7.2 Durability: wood-destroying fungi
Guidance on the use of a wood species in the various use classes depending upon their degree of natural
durability is given in Table 1. In many cases the natural durability of the chosen wood species will be
sufficient to meet service life expectations. If the natural durability of the chosen species is inadequate, a
means to enhance material durability or means to reduce the exposure shall be considered. Wood and
wood-based products of lower durability may be used if exposure control data and/or moisture dynamic
data are available and sufficient as illustrated with a flow diagram in Figure 1. Annexes A, B, and C provide
guidance on verifying the effect of exposure control data and/or moisture dynamic data.
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Table 1 — Wood-destroying fungi — Recommended minimum durability classes of wood species
for use classes
Performance class
Use Class
 short medium long
1 5 5 5
2 5 4 3
3.1 4 4 3
3.2 3 3 2
4 2 2 1
5 2 1 1
 Performance class
 short medium long
Design working life category 1 and 2 3 4 and 5
according to
EC0 EN 1990:2002, Table 2.1

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Figure 1 — Wood-destroying fungi — Decision diagram illustrating the potential to deploy
robust moisture dynamic evidence and exposure control evidence in future to influence
performance outcome
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The following sections consider other biological hazards which on consideration of the region and
product application maybe the critical biological hazard and overrule fungi.
7.3 Durability: wood-destroying beetles
Wood-destroying beetles are present throughout the European area, but the risk of attack varies greatly
from high to insignificant. Reference should be made to local or regional expertise for advice on the risk
of attack by wood-destroying beetles. In situations where there is a significant risk of attack which would
result in an unacceptable loss of function, wood species classified as susceptible in EN 350 should be
treated with a preservative or where regionally acceptable kiln dried. By denying the access for beetles
the use of susceptible wood can be sufficient.
7.4 Durability: termites
In situations where there is a significant risk of termite attack only the heartwood of wood species which
is classified in EN 350 as “durable” (D) or “moderately durable” (M) to termites may be used untreated.
The choice between “durable” (D) and “moderately durable” (M) wood depends upon the specific
requirements, for example for function, end use, expected service life, and the significance of failure. By
denying the access for beetles the use of susceptible wood can be sufficient. Reference should be made to
local or regional expertise for advice on design measures.
7.5 Durability: marine organisms
In situations where there is a significant risk of attack by marine organisms, only the heartwood of wood
species which is classified in EN 350 as “durable” (D) or “moderately durable” (M) to marine organisms
may be used untreated. The choice between “durable” (D) and “moderately durable” (M) wood depends
upon the specific requirements, for example for function, end use, expected service life, and the
significance of failure. By denying the access for marine organisms the use of susceptible wood can be
sufficient. Reference should be made to local or regional expertise for advice on such design measures.
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Annex A
(informative)

Important factors in the relationship between expected service life and
natural durability
A.1Service life
The service life of a timber component will depend upon many factors, not just durability classification
against wood-destroying organisms. For instance, in Use class 3 the design details of a timber component,
which prevent water penetration and collection and encourage drainage and ventilation, together with
local climatic conditions and maintenance procedures, may have an influence on long-term performance.
Similarly, in Use class 4 climatic conditions can have a marked effect on performance. Therefore, it is not
appropriate to base an expected service life solely upon the durability classification. For most
constructional uses there is a generally accepted minimum level of natural durability, which in
conjunction with the other factors gives a service life considered reasonable for a given component. The
selection of a wood with a higher durability classification than that recommended in this standard may
be expected to provide an increased service life for a given end-use.
If constructional components are required to have only a short service life (temporary or semi-
permanent) or if extreme longevity is necessary, it may be appropriate to use wood species with lower
or higher durability classifications than those given in Table 1.
An estimate of expected service life may be obtained by comparing the durability of the wood which is
proposed for use with the known durability and service life of other well-known wood species that have
been used in the same location and for constructions with similar design and maintenance details.
Where fungal attack occurs on lateral surfaces, the service life of a timber component may be influenced
by its thickness. For example, in regions such as parts of central and southern Europe, which experience
long, dry periods, it has been found that timber components having a relatively small cross-section in
ground contact are likely to have a higher service life expectancy than similar components of larger cross-
section due to their ability to dry rapidly.
Biological attack is often progressive, and the service life will therefore also depend upon the amount of
deterioration that can be tolerated by the user before the component is considered to have failed.
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Annex B
(informative)

Example of a factorisation approach for durability-based design and service
life prediction of timber structures
Future classification of performance of wood and wood-based products needs to consider the following
parameters in a quantitative manner:
— macro climate;
— local conditions;
— design;
— surface treatments including coatings;
— decay organisms;
— inherent protective properties due to naturally occurring or artificially impregnated ingredients;
— moisture dynamics;
— susceptibility to cracking and ageing;
— maintenance and inspection intervals.
The current principle of describing both, exposure and material resistance, stepwise as classes needs to
be overcome and a continuous scale for both parameters needs to be established. It is therefore important
that the current classification scheme as well as its application is compatible with an approach for
continuously describing the above listed parameters. We need to move from a class:class system to a
dose:dose system.
Both, exposure and resistance can be expressed as dose, and dose-response relationships are feasible to
describe their effect on the resulting performance of a wood product. The principle of expressing
performance as function of an exposure dose and a resistance dose, both based on a complex dose-
response relationship, is illustrated in Figure B.1.
Performance prediction of wooden structures is generally considered to be a three-step approach. The
design principle describes the climatic exposure on the one hand, and the resistance of the material on
the other hand.
The effect of the above listed influence parameters on the performance of wood in terms of durability
against various biotic agents requires the quantification of the respective dosage for at least three
separate models as illustrated in Figure B.2.
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Figure B.1 — Principle of expressing performance as function of an exposure dose and a
resistance dose, both based on a complex dose-response relationship, here shown exemplarily
for fungal decay


Figure B.2 — Stepwise modelling approach to quantify exposure and resistance on the basis of
dose-reponse relationships and an engineering design principle (DEd = Exposure dose;
DRd = Resistance dose)
The principle
...