CEN/TR 16816:2015

End use performance of wood products - Utilisation and improvement of existing methods to estimate service life

The scope of WG28 Performance Classification is expressed in this Technical Report:
Guidance on the determination of end use performance of wood products: utilization and improvement of existing test methods to estimate service life, in order to give input to the harmonized product standards dealing with the durability requirement of the CPD and future Regulation (EU) No 305/2011 (The Construction Products Regulation CPR).
This Technical Report brings together the evaluations and discussions to date that have occurred within CEN/TC38/WG28 Performance Classification.
This technical report does not address panel products specifically.

Leistungseigenschaften von Holzprodukten bei der Verwendung - Anwendung und Verbesserung von bestehenden Verfahren zur Abschätzung der Lebensdauer

Performances des produits en bois dans leur emploi - Utilisation et amélioration des méthodes existantes pour estimer la durée de vie

Obnašanje izdelkov iz lesa med uporabo - Uporaba in izboljšava obstoječih metod za oceno življenjske dobe

General Information

• Status: Published
• Publication Date: 07-Apr-2015
• ICS: 79.080 - Semi-manufactures of timber
• Technical Committee: CEN/TC 38 - Durability of wood and derived materials
• Drafting Committee: CEN/TC 38/WG 28 - Performance classification
• Current Stage: 6060 - Definitive text made available (DAV) - Publishing
• Start Date: 08-Apr-2015
• Due Date: 06-Sep-2015
• Completion Date: 08-Apr-2015
• Directive: 305/2011 - Regulation (eu) No 305/2011 of the European Parliament and of the Council of 9 march 2011 laying down harmonised conditions for the marketing of construction products and repealing council directive 89/106/eec
• Directive: 89/106/EEC - Construction products
• Ref Project: SIST-TP CEN/TR 16816:2015 - End use performance of wood products - Utilisation and improvement of existing methods to estimate service life

Overview

CEN/TR 16816:2015 - End use performance of wood products - is a CEN Technical Report produced by CEN/TC 38 (Durability of wood and wood‑based products). It provides guidance on the determination of end‑use performance and on the utilisation and improvement of existing test methods to estimate service life of wood products. The report is intended to feed into harmonized product standards addressing the durability requirement of the Construction Products Directive and the Construction Products Regulation (CPD / CPR). Note: this Technical Report does not specifically address panel products.

Key topics

• Service‑life prediction and planning: guidance on linking laboratory and field test results to in‑service performance, including probabilistic approaches and calibration of predictive models (references ISO 15686 concepts).
• Performance classification: outcomes from CEN/TC 38/WG28 about defining performance classes and resistance classes for wood materials.
• Design resistance index (Ir or Rd): a simplified material resistance classification based on durability, moisture dynamics and expert judgment. Example resistance indices from the report include:
  • Class A (very durable heartwood, treated sapwood): 10.0
  • Class B (durable heartwood): 5.0
  • Class C (moderately/slightly durable): 2.0
  • Class D (slightly durable, low permeability): 1.0
  • Class E (sapwood / high sapwood content): 0.7
• Gap analysis of existing standards in TC38 to inform service‑life estimates and suggestions for improving test methods.
• Projects and evidence base: summarizes contributions from initiatives such as COST Action E37, the WoodExter project (cladding and decking pilot model), and links to work in CEN/TC 350 (sustainability / reference service lives) and CEN/TC 351 (release of dangerous substances).

Applications and users

This Technical Report is practical for:

• Standards developers and working groups (CEN, ISO) refining durability requirements and harmonized product standards.
• Manufacturers and product developers of timber cladding, decking and other above‑ground wood components seeking performance‑based specification.
• Designers and specifiers integrating service‑life prediction into building design and lifecycle planning.
• Testing laboratories and researchers improving methods to correlate laboratory or field tests with in‑service durability.
• LCA and sustainability practitioners who need reference service lives for environmental product declarations and lifecycle assessments.

Related standards and concepts

• ISO 15686 (service‑life planning / design life)
• EN 350 (natural durability classification)
• EN 335 (use classes for biological attack)
• Construction Products Regulation (EU) No 305/2011 (CPR)
• Work by CEN/TC 38, CEN/TC 350 and CEN/TC 351

This report helps bridge existing test methods and practical service‑life estimation to support performance‑based durability requirements for wood products. Keywords: CEN/TR 16816:2015, service life, wood products, durability, performance classification, design resistance index, WoodExter, CPD/CPR.

Standards Content (Sample)

SLOVENSKI STANDARD
01-junij-2015
2EQDãDQMHL]GHONRYL]OHVDPHGXSRUDER8SRUDEDLQL]EROMãDYDREVWRMHþLKPHWRG
]DRFHQRåLYOMHQMVNHGREH
End use performance of wood products - Utilisation and improvement of existing
methods to estimate service life
Leistungseigenschaften von Holzprodukten
Performance de fin d'utilisation de produits en bois - Utilisation et amélioration de
méthodes existantes pour améliorer la vie de service
Ta slovenski standard je istoveten z: CEN/TR 16816:2015
ICS:
13.020.60 Življenjski ciklusi izdelkov Product life-cycles
79.020 Postopki v tehnologiji lesa Wood technology processes
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

TECHNICAL REPORT
CEN/TR 16816
RAPPORT TECHNIQUE
TECHNISCHER BERICHT
April 2015
ICS 79.080
English Version
End use performance of wood products - Utilisation and
improvement of existing methods to estimate service life
Performances des produits en bois dans leur emploi - Leistungseigenschaften von Holzprodukten
Utilisation et amélioration des méthodes existantes pour
estimer la durée de vie
This Technical Report was approved by CEN on 21 March 2015. It has been drawn up by the Technical Committee CEN/TC 38.

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
© 2015 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR 16816:2015 E
worldwide for CEN national Members.

Contents Page
Foreword .3
1 Scope .4
2 Background .4
2.1 General .4
2.2 ISO/TC 59/SC14 “Design life” .4
2.3 CEN/TC 350 Sustainability of Construction Words .5
2.4 CEN/TC 351 Construction Products: Assessment of release of dangerous substances .5
2.5 COST Action E37 sustainability through new technologies for enhanced wood durability .5
2.6 WoodExter project .6
2.7 Design value I for resistance factor depending on material .6
Rd
3 Work in this area continued in the Swedish led project WoodBuild 2008-2013.CEN/TC38
Standards: requirements for efficacy .8
3.1 Preservative treated wood .8
3.2 Naturally durable wood .9
4 Guidance on the determination of end use performance of wood products . 10
5 Guidance on utilization and improvement of existing methods to estimate service life . 11
5.1 General . 11
5.2 Gap analysis of existing standards in TC38 to inform on service life . 11
6 Actions . 30
6.1 General . 30
6.2 WG21 . 30
6.3 WG23 . 31
6.4 WG25 . 31
6.5 WG24 . 31
7 Acknowledgements . 32
Bibliography . 33

Foreword
This document (CEN/TR 16816:2015) has been prepared by Technical Committee CEN/TC 38 “Durability of
wood and wood-based products”, the secretariat of which is held by AFNOR.
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.
1 Scope
The scope of WG28 Performance Classification is expressed in this Technical Report:
Guidance on the determination of end use performance of wood products: utilization and improvement of
existing test methods to estimate service life, in order to give input to the harmonized product standards
dealing with the durability requirement of the CPD and future Regulation (EU) No 305/2011 (The Construction
Products Regulation CPR).
This Technical Report brings together the evaluations and discussions to date that have occurred within
CEN/TC38/WG28 Performance Classification.
This technical report does not address panel products specifically.
2 Background
2.1 General
The development of performance-based design methods for durability requires that models are available to
predict performance in a quantitative and probabilistic format. The relationship between performance during
testing and in service needs to be quantified in statistical terms and the resulting predictive models need to be
calibrated to provide a realistic measure of service life, including a defined acceptable risk of non-conformity.
Service-life prediction or planning is a process for ensuring that, as far as possible, the service life of a
building will equal or exceed its design life, while taking into account (and preferably optimising) its life-cycle
costs (ISO 15686 [1]). For a long time, the international organizations CIB and RILEM have been leading this
development, which has had an impact on standardization work nationally, regionally, and globally through
ISO.
Service-life prediction should be integrated into the design process for constructions, but it is also applicable
to existing buildings and other construction works.
Drivers for establishing service-life planning methodology and routines include the need for building owners to
be able to forecast and control costs throughout the design life of a building or construction. It also influences
the reliability of constructed assets, and hence the health and safety of users.
The construction sector is under pressure to improve its cost effectiveness, quality, energy efficiency and
environmental performance and to reduce the use of non-renewable resources. A key issue for the
competitiveness of wood is the delivery of reliable components of controlled durability with minimum
maintenance needs and life-cycle costs.
The importance of service-life issues is reflected in the Construction Products Directive (CPD) with its six
essential requirements, which should be fulfilled by construction products during a ‘reasonable service life’.
2.2 ISO/TC 59/SC14 “Design life”
The development of performance-based design methods for durability requires that models are available to
predict performance in a quantitative and probabilistic format. The relationship between performance during
testing and in service needs to be quantified in statistical terms and the resulting predictive models need to be
calibrated to provide a realistic measure of service life, including a defined acceptable risk of non-conformity.
Service-life prediction or planning is a process for ensuring that, as far as possible, the service life of a
building will equal or exceed its design life, while taking into account (and preferably optimising) its life-cycle
costs (ISO 15686 [1]). For a long time, the international organisations CIB and RILEM have been leading this
development, which has had an impact on standardization work nationally, regionally, and globally through
ISO.
Service-life prediction should be integrated into the design process for constructions, but it is also applicable
to existing buildings and other construction works.
Drivers for establishing service-life planning methodology and routines include the need for building owners to
be able to forecast and control costs throughout the design life of a building or construction. It also influences
the reliability of constructed assets, and hence the health and safety of users.
The construction sector is under pressure to improve its cost effectiveness, quality, energy efficiency and
environmental performance and to reduce the use of non-renewable resources. A key issue for the
competitiveness of wood is the delivery of reliable components of controlled durability with minimum
maintenance needs and life-cycle costs.
The importance of service-life issues is reflected in the Construction Products Directive (CPD) with its six
essential requirements, which should be fulfilled by construction products during a ‘reasonable service life’.
2.3 CEN/TC 350 Sustainability of Construction Words
CEN/TC 350 is responsible for the development of voluntary horizontal standardized methods for the
assessment of the sustainability aspects of new and existing construction works and for standards for the
environmental product declaration of construction products.
The objective is to ensure that LCA-based data for environmental product declarations are consistent,
comparable, verifiable and scientifically based. Since the life cycle has to be defined, it is essential to include
information on service lives, including reference service lives.
Methods for sustainability assessments should be based on a performance-based approach, and should
cover environmental, social and economic performance.
2.4 CEN/TC 351 Construction Products: Assessment of release of dangerous substances
The work of CEN/TC 351 is directed to the area covered by the Biocidal Products Directive and REACH.
Indicators, criteria and developed standards will have significant influence in the future on the materials
available for construction products and on service-life design options.
2.5 COST Action E37 sustainability through new technologies for enhanced wood durability
The Task Force Performance Classification (TFPC) was established at the COST Action E37 workshop in
Ljubljana in 2004 [2]. Its aim was to outline principles for a performance-based classification of wood
durability, in particular in using the natural durability of untreated wood and for modified wood products,
traditional and non-traditional treatments and non-biocidal measures for wood protection.
The COST Action ended in September 2008, and the TFPC submitted a final report for inclusion in the overall
documentation of the Action [3]. Standards for durability of wood and wood-based products, not least those
produced by CEN/TC 38 Durability of wood and wood-based materials, were of primary interest to the TFPC.
They considered that the present standards could not deliver adequate performance-based data. One goal of
the Task Force was therefore to address the way durability is treated in standardization. It was conceived that
well-founded proposals on amalgamating modern, material-independent methods of service-life prediction and
design with traditional wood assessment methods would be of direct use, e.g. to CEN/TC 38 and the
construction industry.
The TFPC recognized the use of Reference Service Life (RSL) as a basis for estimations of Estimated Service
Life (ESL). The estimates are not necessarily reached by use of the Factor Method as in ISO 15686, but the
basic principle is useful. To develop a range of performance classes, the scientific community must connect
better and cooperate with user groups and stakeholders and define reference products that can be evaluated
under reference service conditions. Test results on any commodities, products and components will then be
compared with agreed RSLs, and this can form the foundation for a range of performance classes. During this
development, existing use classes have to be taken into account and, if necessary, adapted to suit a
forthcoming system for performance classification. As an input to Factor A (Quality of components) in the
Factor Method, it will be necessary to define a range of Resistance Classes to feed into the assessments.
This work is carried forward in CEN/TC 38 WG28 and the WoodExter project.
2.6 WoodExter project
The WoodExter project [4] (2007 – 2010) was a collaborative pan-European-funded research project
supported by WoodWisdom-Net and the Building with Wood industry initiative. Its objective was to take the
first steps towards introducing performance-based engineering design for wood and wood-based building
components in outdoor above-ground situations. This enables capture of the benefits of ‘design for durability’
and has delivered a practical engineering tool for service-life estimation based on a novel methodology. The
project focused on cladding and decking as two test case products to rigorously assess this methodology.
The project aims were to:
— characterize climatic influence on performance of timber cladding;
— characterize new and existing techniques as in-service indicators of performance prediction;
— combine the above in an engineering-based model;
— calibrate and rigorously test the model for the selected Use Class 3 products, cladding and decking;
— transfer knowledge to enable confident specification of timber cladding and decking.
A pilot model has been developed in the WoodExter project incorporating key input data and the interactions
between them that influence performance of cladding www.kstr.lth.se/guideline. The consequence class
depends on the severity of consequences in case of non-performance and is described by the factor γ .
d
The exposure index I is conceived as a ‘characteristic (safe) value’ accounting for uncertainties. The
sk
exposure index is assumed to depend on:
— geographical location determining global climate;
— local climate conditions;
— the degree of sheltering;
— distance from the ground;
— detailed design of the wood component;
— use and maintenance of coatings.
2.7 Design value I for resistance factor depending on material
Rd
The design resistance index I for selected wood materials is determined on the basis of resistance class
Rd
according to Table 1. This is a simplified first step for a material resistance classification based on a balanced
expert judgment of moisture dynamics and durability class. The resistance class term is based on a
combination of durability class data according to EN 350-2, test data, experience of treatability and
permeability for wood species as well as experience from practice.
Biological durability is the key factor determining performance for wood in different use classes. The robust
laboratory and field test methods that exist make it possible to assign a durability rating to timber linked to the
intended use class according to EN 335, assuming a worst case scenario. Other factors determine the
likelihood of the worst case scenario occurring in practice.
The natural durability of wood is classified into durability classes as described in EN 350-1 and presented as
durability classes for heartwood of timber species in EN 350-2. Durability class is a classification on five levels
from non-durable to very durable. This is based on decades of data from ground contact field trials for use
class 4. The natural durability for a wood species can vary widely.
Table 1 — Resistance classification of selected wood materials and corresponding design resistance
index
I
Material a
Rd
Examples of wood materials
resistance
class
A Heartwood of very durable tropical hardwoods, e.g. 10,0
afzelia, robinia (durability class 1)
Preservative-treated sapwood, industrially processed to
meet requirements of use class 3.
B Heartwood of durable wood species e.g. sweet chestnut 5,0
(durability class 2)
C Heartwood of moderately and slightly durable wood 2,0
species e.g. Larch and Scots pine (durability class 3 and
4,)
D Slightly durable wood species having low water 1,0
permeability (e.g. Norway Spruce)
E Sapwood of all wood species (and where sapwood 0,7
content in the untreated product is high)
a
For the majority of wood materials there is variability in material resistance. The material
resistance classification should defer to local knowledge based on experience of performance of
cladding and decking and where this is not available field test data and then laboratory test data. It is
possible that a classification with different design resistance indices may need to be adopted for
specific regions or countries, based on practical experience e.g. from the use of a material in that
region.
For out of ground contact (e.g. exterior wood cladding) the challenge is to translate durability class from use
class 4 to use class 3. In EN 350-1 the term “markedly different” is used to describe the additional benefits of
low permeability on the performance of wood out of ground contact. Expert advice is recommended for
assigning the material resistance class for wood materials such as:
Preservative treated wood is often a combination of mixed treated heartwood and sapwood. The treated
sapwood should be thoroughly treated and enhanced to durability class 1. The heartwood is more resistant to
treatment and the enhancement of the heartwood can be considered to be slightly higher than the natural
durability class of the heartwood for the species (EN 350-2). Therefore, for preservative treated decking it may
be more sensible to take a mid-point between the resistance class of the treated sapwood and the treated
heartwood. E.g. for pine heartwood treated (resistance class C) and pine sapwood treated (resistance class
A) the overall batch of preservative treated wood should then be classified as resistance class B.
For untreated wood if there is a mixture of heartwood and sapwood present in the wood species then the
material resistance can either be classified as the mid-point between the class of the heartwood (resistance
class A to D) and the sapwood (resistance class E). If this risk is not acceptable then the material resistance
class should be taken as the worst case (E), the least resistant competent of the overall material.
The durability of modified wood, e.g. acetylated, furfurylated and thermally modified, is specific to the
technologies employed and may vary between specifications for the different materials. Expert advice is
recommended for assigning the material resistance class for modified wood.
The input data are described by Thelandersson et al. [5] (2011) and the design of a detail is made in the
following steps:
1) Choose consequence class to determine γ
d;
for the exposure index depending on the geographic location of interest;
2) Determine a base value I
S0
3) Find a correction factor for the exposure index to account for the local climate conditions (meso- or micro-
climate). Factors of importance are orientation, overall geometry of the structure, nature of the
surroundings;
4) Find appropriate correction factors for:
— Sheltering conditions;
— Distance from ground;
— Detailed design of the wood component considered.
for the exposure index.
Steps 2–4 give a characteristic value I
Sk
for the resistance index;
5) 5Choose material to determine a design value I
Rd
6) Check performance by the condition:
I =γ ⋅I ≤ I
d Sk
Sd Rd
Where:
I is performance
Sd
γ is consequence class
d
I is characteristic value for the exposure index;
Sk
I is design value for the resistance index
Rd
7) If non-performance, change inputs in some or all of steps 2, 3, 4 and 5.
3 Work in this area continued in the Swedish led project WoodBuild 2008-
2013.CEN/TC38 Standards: requirements for efficacy
3.1 Preservative treated wood
The majority of CEN/TC38 efficacy tests are relevant to preservative treated wood. The CEN/TC38 system
involves a framework in which specifications for preservation can be made on a country-by country basis
depending on the requirements of any given country, yet using the same set of efficacy tests. This framework
for specification is laid down in European standards EN 351-1 and EN 599-1. Of these it is EN 599-1 which
governs the choice of appropriate test methods depending on the use class in which the treated wood is to be
used.
EN 599-1 ensures the appropriate efficacy tests are performed for each use class (including the correct choice
of artificial aging procedure). Some efficacy tests are considered “minimum requirements” while others are
considered to be “additional / local tests”, which are not necessarily required in all European countries. Tests
differ if the preservative is a penetrating preservative or a superficial preservative. Table 2 summarizes the
requirements for the testing of a penetrating preservative in accordance with EN 599-1.
Table 2
Minimum and additional test requirements for penetrating preservatives according to Use
Class, as specified in EN 599–1
Use Pre-conditioning Minimum requirements Additional / local tests
Class requirement
1 EN 73 EN 47 and/or EN 117
EN 49–2 and/or
EN 20–2
2 EN 73 EN 113 (brown rot fungi only) UC1 tests
EN 152
3 EN 73 EN 113 (brown rot fungi only) UC1 tests
EN 84 (EN 84 not required
EN 152
if EN 330 conducted)
EN 113 (on C versicolour)
EN 330
4 EN 73 EN 113 (brown rot fungi and UC1 tests
C. versicolour)
EN 84 EN 152
ENV 807
EN 252
5 EN 73 As UC4 plus UC1 tests
EN 84 EN 275 EN 152
The vast majority of the efficacy tests are conducted on small blocks of pine sapwood that are defect-free.
They are mainly conducted in conditions where the test organism is the only organism present (e.g. in the
case of basidiomycetes pure cultures are used) and in conditions conducive to the wood degrading activity of
that organism.
All the minimum requirement tests are laboratory efficacy tests, with the exception of EN 275 for UC5. It is not
possible to conduct efficacy tests against all organisms which may attack wood in practice. Test organisms
have been chosen to be representative of the types of organism that are encountered in the relevant use
class.
The results from each of the relevant efficacy tests are assessed using guidelines given in EN 599-1 and a
“biological reference value” (brv) is calculated for each test in terms of the application of preservative required
to pass the test. The highest of the brv’s from the tests required for a particular use class is known as the
“Critical Value” (CV) of that preservative for the given use class.
The CV is not necessarily the retention requirement. In order to calculate the retention requirement for a
preservative the CV can be adjusted. This adjustment is done within a given country to take account of local
conditions and expectations.
3.2 Naturally durable wood
The natural durability classes of timber species commonly traded in Europe are given in EN 350-2. These
durability classes are based on long term experience and on field performance in UC4 exposure. EN 350-1
describes assessment methods for naturally durable species for which the same experience is not necessarily
available and that are not listed in EN 350-2. The assessment of these species is based on EN 252 (ground
contact field test), though a laboratory test based on EN 113 (basidiomycete fungi) is permitted to derive a
provisional natural durability class which can be used until the field test results become available. Two further
technical specifications have been developed by CEN/TC 38 to test natural durability. CEN/TS 15083-1 is a
laboratory test against basidiomycete fungi, and CEN/TS 15083 is a laboratory test against soft rot fungi.
4 Guidance on the determination of end use performance of wood products
Certain aspects peculiar to wood products should be taken into account when estimating the service life of
construction products and planning the service life of buildings and constructions. These include:
— biological durability: a key factor for wood products in service;
— service conditions: period of wetness of the substrate, and what influences this, is the main factor in
determining risk of decay. ISO 21887:2007 [6] defines a system of ‘service classes’ for wood products
called Use Classes;
— insect hazard: damage by wood-boring insects and termites is affected more by whether the insects are
present in the geographical region than by the service conditions;
— assessment procedures: standard tests for the biological durability of wood, especially of treated wood
products, already exist (EN 599);
— natural variability: as wood is a natural material with large inherent variations, it is more realistic to define
broad service classes than precise service life in years.
Broadly, for each Use Class the expected service life is determined by a combination of the biological
durability of the timber and the physico-chemical factors that put the products at risk of biological degradation.
The intended or designed service life can be met by selecting a timber of suitable biological durability or by
reducing or eliminating the factors that put wood at risk of degradation. In practice, service life is usually met
by a combination of the two.
By assigning values to these two characteristics it is possible to derive a value equivalent to a service class.
This approach is in keeping with the aims of the factor method and compatible with it.
Considering two unique features of wood products more closely:
— Biological durability is the key factor determining performance in different use classes. Existing laboratory
and field test methods make it possible to assign a durability rating to any timber product linked to the
intended Use Class, assuming a worst-case scenario. Other factors determine the likelihood of the
scenario. In assessing the biological durability the principle is to determine performance against reference
service products for each use class and service-life period;
— Period of wetness of the substrate is key for the development of timber decay. This is affected by
environmental parameters (including design, building physics, exposure, and maintenance) which have a
marked effect on performance and vary greatly across Europe. No internationally agreed methods for
assessing these parameters exist, but various national approaches based on experience take them into
account. Any one of these parameters or a combination thereof can have an over-riding influence on
performance.
At present, a single value for each factor should be allocated at a national approval level. This allows national
experience for certain products to play a key role. For example, untreated spruce, a non-durable timber, is
known to achieve the desired service life when used as painted exterior cladding in the Nordic countries, but
this is not always the case in other European countries. Therefore in that region, a high rating can be allocated
to the product making it unnecessary to invoke enhanced durability. The national schemes may well follow the
ISO methods in detail.
Notwithstanding the above, if factors outside the control of moisture risk exist, such as the risk of wood-
destroying beetles or termites, then this invokes the need for enhanced durability or protective design
measures to eliminate the risk.
This information concentrates on the biological performance of wood-based products. Although this is a most
important aspect, other factors in ISO 15686 also need to be taken into account.
A significant, if not the most significant, challenge is to be able to predict the performance of products (e.g.
window, woodpole, timber deck, structural beam) from tests that by their very nature do not consider the
primary influences of service life such as design, exposure and maintenance. CEN/TC38 tests almost
exclusively consider only the material, and an idealised material (e.g. preservative treated sapwood), and the
primary influence of material resistance not the moisture risk. Termites and insects might present a special
case. They have to be present so there is a need to consider the product use location (e.g. South France) and
insects and termites as an ‘add on’ to service life prediction. Beyond that we may just accept that the reliable
material resistance (durability + permeability) data are the only influence CEN/TC 38 may have over
performance classification and service life prediction. In which case our insect and termite tests should have a
high predictive ability and be good at classifying the performance of wood and wood-based materials.
The primary two means of delivering performance for a UC3 wood product are design of the product (and its
execution in the real building) and the exposure aspects (meso, macro, micro). Design and exposure can be
controlled to deliver a wood product that meets a desired service life through elimination of moisture risk.
However, it can be difficult to achieve and risks are high of non-conformities (e.g. poor workmanship on
installation of the window) which will compromise performance. The third means is the material resistance. For
most of our tests we classify the performance of preservative treated wood (the material) not the product. The
more complex the construction product the further away from the prediction we are with our tests. The
material resistance is a hugely important part of service life modelling so perhaps we can accept that this is all
we will achieve – but then we must be sure that how we measure material resistance, against which reference
products is appropriate for our nee
...