ISO 13823:2008

General principles on the design of structures for durability

ISO 13823:2008 specifies general principles and recommends procedures for the verification of the durability of structures subject to known or foreseeable environmental actions, including mechanical actions, causing material degradation leading to failure of performance. It is necessary to insure reliability of performance throughout the design service life of the structure. Fatigue failure due to cyclic stress is not within the scope of ISO 13823:2008.

Principes généraux du calcul des constructions pour la durabilité

General Information

• Status: Published
• Publication Date: 08-Jun-2008
• ICS: 91.080.01 - Structures of buildings in general
• Technical Committee: ISO/TC 98/SC 2 - Reliability of structures
• Drafting Committee: ISO/TC 98/SC 2 - Reliability of structures
• Current Stage: 9093 - International Standard confirmed
• Start Date: 15-Feb-2024
• Completion Date: 13-Dec-2025

Overview

ISO 13823:2008 - "General principles on the design of structures for durability" - provides high-level, practical guidance for the verification of structural durability under known or foreseeable environmental actions. It establishes a cause‑and‑effect framework linking the structure environment, transfer mechanisms, environmental actions, and action effects that lead to material degradation and potential failure. ISO 13823 integrates durability considerations into the widely used limit‑states design approach (see ISO 2394) and focuses on ensuring reliable performance over the specified design life. (Note: fatigue from cyclic stress is explicitly excluded.)

Key topics and requirements

• Scope and definitions: Clear terminology (e.g., action effect, agent, transfer mechanism, initiation limit state, serviceability and ultimate limit states) to harmonize durability language across standards.
• Basic concepts for verifying durability: Framework for identifying environmental influences, mechanisms that transfer those influences into material agents, and the resulting effects on components.
• Durability requirements: Principles for specifying design life, characteristic service life, and target reliability of structures and components.
• Service‑life prediction methods: Recommended approaches include prediction based on experience, modelling (conceptual and mathematical), and testing.
• Design formats: Use of the partial factor method and limit‑states formats to account for uncertainties and variabilities in basic variables.
• Strategies for durability design: Guidance on maintenance, inspection, repair strategies and considerations of difficulty/cost of replacement and consequences of failure.
• Informative annexes: Practical examples of limit‑states applications, environmental agents, transfer mechanisms, material‑specific actions and recommended procedures for ensuring durability.

Practical applications and users

ISO 13823 is intended for:

• Structural engineers and designers integrating durability into structural design and detailing.
• Asset managers and facility owners planning service life, maintenance and replacement strategies.
• Code writers and standards developers harmonizing durability requirements with limit‑states design.
• Materials scientists and researchers developing predictive models for material degradation.
• Construction and inspection professionals using the framework for risk‑based durability verification.

Typical applications include buildings, bridges and other constructed assets where environmental exposure (corrosion, chloride ingress, moisture, UV, biological attack) can reduce performance over time.

Related standards

• ISO 2394:1998 - General principles on reliability for structures (limit‑states method)
• ISO 15686 (all parts) - Service‑life planning for buildings and constructed assets
• ISO 13822:2001 - Assessment of existing structures
• ISO 3898 / ISO 8930 and national standards (e.g., AS 5604) for material durability ratings

By using ISO 13823:2008, practitioners can better predict service life, set design life targets, and apply consistent, risk‑based durability verification across projects.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 13823
First edition
2008-06-15
General principles on the design of
structures for durability
Principes généraux du calcul des constructions pour la durabilité

Reference number
©
ISO 2008
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ii © ISO 2008 – All rights reserved

Contents Page
Foreword. iv
Introduction . v
1 Scope .1
2 Normative references .1
3 Terms and definitions .1
4 Symbols .4
5 Application .4
6 Basic concepts for verifying durability .5
6.1 General.5
6.2 Structure environment .5
6.3 Transfer mechanisms.5
6.4 Environmental action .5
6.5 Action effects .6
6.6 Limit states .6
7 Durability requirements .7
7.1 Basic durability requirement .7
7.2 Formats for checking durability.8
8 Design life of a structure and its components, t .11
D
8.1 Structure .11
8.2 Components.11
8.3 Component service life related to the design life of the structure .11
8.4 Difficulty and cost of maintenance or replacement .11
8.5 Consequences of failure .11
8.6 Selection of target reliability.11
9 Predicted service life, t .12
SP
9.1 General.12
9.2 Prediction based on experience.13
9.3 Prediction based on modelling .13
9.4 Prediction based on testing.14
10 Strategies for durability design.14
Annex A (informative) Examples of the application of the limit-states method .15
Annex B (informative) Examples of influences (structure environment) and agents (environmental
action) .26
Annex C (informative) Examples of transfer mechanisms.32
Annex D (informative) Environmental actions for structural materials and their control .34
Annex E (informative) Procedures for ensuring durability .37
Bibliography .39

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 13823 was prepared by Technical Committee ISO/TC 98, Bases for design of structures, Subcommittee
SC 2, Reliability of structures.
iv © ISO 2008 – All rights reserved

Introduction
The limit-states method, as developed in ISO 2394, has been adopted and used for preparing and
harmonizing national and regional structural design standards and codes around the world. Although
ISO 2394 includes durability in its principles, the limit-states method has not been developed for failures due
to material deterioration to the extent that it has for failures due to actions such as gravity, wind, snow and
earthquake. Also, many premature failures have occurred because of a lack of understanding of material
deterioration in the structural engineering profession.
The first objective in developing this International Standard is to improve the evaluation and design of
structures for durability by the incorporation of building-science principles into structural-engineering practice.
These principles are now being taught in engineering courses in many countries. This goal is achieved by the
incorporation of these principles into the limit-states method currently used in structural engineering practice
and defined in ISO 2394, and by the use of a common, user-friendly terminology for physical phenomena.
Developments have recently taken place in mathematical modelling of the mechanisms that cause material
deterioration and failure. There is a need to harmonize the use of these models in practice by using the limit-
states method and a common terminology.
The second objective in developing this International Standard is to provide a framework for the development
of mathematical models to predict the service life of components of the structure. Such models are currently
being developed, for example, for concrete slabs subjected to chloride diffusion from de-icing salts. These
models are material-dependent and, therefore, are being developed by other ISO/TCs. The goal of this
International Standard is to ensure that all analytical models are incorporated into the limit-states method, the
same as currently used for the verification and design of structures for gravity, wind, snow and earthquake
actions.
While this International Standard does not address design procedures for durability, it lays a solid foundation
by identifying a process starting from the structure’s environment, followed by mechanisms that transfer this
environment into environmental actions on component materials leading to action effects, such as damage
(see Figure 1). It is necessary to take this cause-and-effect process into account in developing methods for
the prediction of service life.
This International Standard is intended to serve a similar unification role as ISO 2394 has had over the past
30 years for the verification and design of structures against failure due to mechanical actions, such as
gravity, wind, snow and earthquake.
This International Standard does not directly address sustainability for structures, except through referencing
in notes in 8.4 and Clause 10. Most considerations of sustainability, such as the choice of material as it affects
waste and energy consumption, are outside the scope of this International Standard. Sustainability
considerations in the future, however, are expected to increase the emphasis on choice of materials,
technologies, inspectability, maintenance, repair and replacement in the planning and design of structures.
It is intended that this International Standard be used in parallel with ISO 15686 (all parts) on service-life
planning for buildings and construction assets. Service-life prediction for structures based on experience and
testing are contained in ISO 15686 (all parts). Service-life prediction of structures based on the modelling of
durability, in addition to experience and testing, using conceptual as well as mathematical models, are
described in this International Standard.

INTERNATIONAL STANDARD ISO 13823:2008(E)

General principles on the design of structures for durability
1 Scope
This International Standard specifies general principles and recommends procedures for the verification of the
durability of structures subject to known or foreseeable environmental actions, including mechanical actions,
causing material degradation leading to failure of performance. It is necessary to ensure reliability of
performance throughout the design service life of the structure.
Fatigue failure due to cyclic stress is not within the scope of this International Standard.
NOTE Reference can be made to ISO 2394 for failure due to fatigue.
2 Normative references
The following referenced documents are indispensable for the application 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.
ISO 2394:1998, General principles on reliability for structures
ISO 3898:1997, Bases for design of structures — Notations — General symbols
ISO 8930:1987, General principles on reliability for structures — List of equivalent terms
ISO 13822:2001, Bases for design of structures — Assessment of existing structures
ISO 15686-5, Buildings and constructed assets — Service-life planning — Part 5: Life-cycle costing
ISO 15686-6, Buildings and constructed assets — Service life planning — Part 6: Procedures for considering
environmental impacts
AS 5604, Timber — Natural durability ratings
3 Terms and definitions
3.1
action effect
S
effect of an environmental action on a component of a structure (e.g. damage, reduced resistance, internal
force, displacement, change in appearance)
3.2
agent
chemical or biological substance or physical process (e.g. UV) or biological (e.g. insect attack) process that,
alone or together with other agents, including contaminants in the material itself, acts on a structure or
component to cause material degradation
3.3
basic variable
variable describing the structure environment, transfer mechanism, environmental action, action effect,
material property or geometrical quantity
3.4
characteristic value of a basic variable
specified fractile of the variable determined in accordance with ISO 2394
3.5
characteristic service life
value of a predicted service life chosen either on a statistical basis, so that it has a specified probability of
being more unfavourable (i.e. lower), or on a non-statistical basis, for instance based on acquired experience
3.6
component
any part of the structure and any non-structural part that may affect the durability of the structure
3.7
degradation
material deterioration or deformation that leads to adverse changes in a critical property of a component
3.8
design value of a basic variable
factored characteristic value of the variable determined in accordance with ISO 2394
3.9
design life
specified period of time for which a structure or a component is to be used for its intended purpose without
major repair being necessary
NOTE This term is equivalent to design working life in ISO 2394:1998, 2.2.15.
3.10
durability
capability of a structure or any component to satisfy, with planned maintenance, the design performance
requirements over a specified period of time under the influence of the environmental actions, or as a result of
a self-ageing process
3.11
environmental action
chemical, electrochemical, biological, physical and/or mechanical action causing material degradation of a
component
NOTE 1 See Figure 1.
NOTE 2 See also environmental influences in ISO 2394:1998, 6.3.
3.12
failure
loss of the ability of a structure or component to perform a specified function
3.13
initiation limit state
ILS
state that corresponds to the initiation of significant deterioration of a component of the structure
NOTE See 6.6.
3.14
limit state
state beyond which a structure or component no longer satisfies the design performance requirements
3.15
maintenance
combination of all technical and associated administrative actions during a component’s service life (3.21)
with the aim of retaining it in a state in which it can perform its required functions
2 © ISO 2008 – All rights reserved

3.16
model
simplified conceptual or mathematical idealization or test set-up simulating the structure environment, transfer
mechanisms, environmental action, action effects and structural behaviour that can lead to failure
NOTE See Figure 1.
3.17
partial factor method
calculation format in which allowance is made for the uncertainties and variabilities of the basic variables by
means of characteristic values, partial factors and, if relevant, additive quantities
3.18
predicted service life
service life (3.21) estimated from recorded performance, previous experience, tests or modelling
3.19
reliability
ability of a structure or component to satisfy the specified design performance requirements within the design
service life
3.20
repair
restoration of a structure or its components to an acceptable condition by the renewal or replacement of worn,
damaged or deteriorated components
3.21
service life
actual period of time during which a structure or any of its components satisfy the design performance
requirements without unforeseen major repair
3.22
serviceability limit state
SLS
state that corresponds to conditions beyond which specified serviceability requirements for a structure or its
components are no longer satisfied
NOTE See 6.6.
3.23
structure environment
external or internal influences (e.g. rain, de-icing salts, UV, humidity) on a structure that can lead to an
environmental action
NOTE See Figure 1.
3.24
transfer mechanism
mechanism by which influences in the structure environment are, over time, transferred into agents on and
within components or prevent such transfer
NOTE See Figure 1.
3.25
ultimate limit state
ULS
state associated with collapse, or with other similar forms of structural failure
NOTE See 6.6.
4 Symbols
P
probability
P probability of failure
f
P target probability of failure
target
P target probability of failure, serviceability limit state
target,SLS
P target probability of failure, ultimate limit state
target,ULS
R resistance
mean resistance
R
S
action effect
mean action effect
S
S serviceability limit
lim
t time, expressed in years
t design life, expressed in years
D
t time after initiation of degradation, expressed in years
exposed
t reference service life, expressed in years; see 9.3.2
ref
t service life, expressed in years, that occurs or that is represented by a mathematical probability
S
function
t characteristic value of t , expressed in years
Sk S
t predicted service life, expressed in years
SP
t time to initiation of degradation, expressed in years
start
X basic variable for modelling t , S and R
i start
Y basic variable for modelling t , S and R
i exposed
γ partial factor for predicted service life; see Equation (4)
S
5 Application
It is the intention that the general principles in the verification and design of structures and components for
durability in this International Standard be used whenever a minimum service life is required, for new
structures as well as for the assessment of existing structures.
The considered components include non-structural components that can affect the durability of the structure.
NOTE Because of the complex nature of the degradation and damage of structures, durability of structures is related
not only to structural components but also to non-structural components. However, non-structural components, such as
equipment, are generally not included in this International Standard because they are normally easily replaced.
The general principles apply to the design phase as well as to planning maintenance, repair and replacement
measures, in failure investigations, etc. However, additional considerations can apply to existing structures.
For existing structures, procedures and criteria in this International Standard may be modified to take into
account inspection and test results concerning the quality of workmanship, conditions of maintenance and
variation in the durability of materials. In addition, if they can be justified (see ISO 13822), lower target
reliability levels may be used for existing structures.
4 © ISO 2008 – All rights reserved

6 Basic concepts for verifying durability
6.1 General
This International Standard recommends the use of the limit-states method shown in Figure 1 for the design
and verification of structures for durability. For any component of the structure, this requires an understanding
of the structure environment (6.2), the transfer mechanisms (6.3), the environmental action (6.4), leading to
action effects (6.5) that can result in the failure of the component.
For examples of the application of the limit-states method in Figure 1, see Annex A.
NOTE Environmental action can also occur as the result of a self-ageing process (see 6.3, Note 3).
6.2 Structure environment
The structure environment contains influences, such as air, rain, contaminants, temperature, biological life and
solar radiation, that provide agents such as moisture and oxygen that can affect the durability of components.
These influences occur outside (climate, ground or body of water) or inside (climate, chemicals) the structure.
For examples of influences in the structure environment, see Annex B.
6.3 Transfer mechanisms
Transfer mechanisms, such as gravity, condensation and drainage, promote or prevent transfer of
environmental influences into agents causing environmental action on or within the components of the
structural system.
For examples of transfer mechanisms, see Annex C.
NOTE 1 Modelling of the deterioration process requires an understanding of the transfer mechanisms and
environmental actions leading to failure. These are based on knowledge of the materials of the components and the
microclimate in the vicinity of the components of the structure.
NOTE 2 Moisture, with or without contaminants, is the most important agent causing premature deterioration. The
application of building science principles permits the generation of models — conceptual, mathematical or test set-up —
for predicting the mechanisms, paths, volumes and forms of moisture that components are required to accommodate and
to resist.
NOTE 3 Transfer mechanisms can also include a manufacturing process that results in a self-ageing degradation
without agents transferred from the structure environment, for example the addition of sea sand into the concrete mix.
6.4 Environmental action
An environmental action, such as corrosion, decay or shrinkage, is a chemical, electrochemical, biological
(e.g. insect attack), physical (e.g. UV) or mechanical action causing material deterioration or deformation.
Except for mechanical action, an environmental action is the consequence of the expected environmental
agents, such as moisture, oxygen and temperature, the chemical, electrochemical and physical properties of
the materials of the components, and the interaction of the different components, including electrochemical
(e.g. galvanic corrosion) and physical (e.g. deformation) interactions. Environmental actions, such as
corrosion of steel, decay of wood, shrinkage or freeze-thaw of cement-based materials such as masonry or
concrete, can result in loss of performance.
For examples of agents affecting different materials, see Annex B.
For examples of environmental actions, see Annex D.
a
Both conceptual and mathematical.
Figure 1 — Limit-states method for durability
6.5 Action effects
Action effects include damage, loss of resistance, internal force/stress or unacceptable appearance due to
material deterioration, or displacement due to material deformation. An action effect can result in the loss of
performance as defined by one or more of the limit states given in 6.6.
For examples of action effects, see Annex D.
6.6 Limit states
6.6.1 Ultimate limit state
For material deterioration resulting in failure due to loss of resistance, the ultimate limit state is defined when
the resistance of the component or structure becomes equal to, or less than, the internal mechanical force.
See Clauses A.1 and A.2.
6 © ISO 2008 – All rights reserved

6.6.2 Serviceability limit states
For material degradation, the serviceability limit states are defined by
⎯ local damage (including cracking) or change in appearance that affects the function or appearance of
structural or non-structural components,
⎯ relative displacements that affect the function or appearance of structural or non-structural components.
6.6.3 Initiation limit state
This limit state is defined by the initiation of deterioration of a component that precedes the occurrence of the
serviceability or ultimate limit states. The time to reach this limit state is designated by t in Figure 1. See
start
Clause A.3.
NOTE 1 A deterioration or deformation occurring on or inside a structure does not necessarily mean failure. Therefore,
it is important to consider not only the environmental action and action effects, but also the limit states (e.g. fracture,
movements, gaps, appearance, material weakening) that correspond to functional failure of the component for its intended
use. Examples are given in Annex D of the forms of failure associated with prevalent environmental actions for materials.
NOTE 2 Although not within the scope of this International Standard, mould growth due to moisture accumulation on
components can also serve as a limit state affecting human health.
7 Durability requirements
7.1 Basic durability requirement
Structures and their components shall be conceived, designed, constructed and operated, inspected,
maintained and repaired in such a way that, under foreseeable environmental conditions, they maintain their
required performance during their design lives with sufficient reliability for the safety and comfort of users and
the intended use of the structure.
The service life, t , of the structure and its components shall meet or exceed the design life, t , as expressed
S D
in Equation (1):
t W t (1)
S D
When a component is protected against agents (e.g. concrete cover of reinforcement, zinc coating of steel,
preservative treatment of wood), the service life, t can be determined as given in Equation (2) (see Figure 1):
,
S
t = t + t (2)
S start exposed
where
t is the time of the initiation of deterioration;
start
t is the service life after initiation of the deterioration.
exposed
The service life of the structure is based on the service lives of all the components, management procedures,
inspection, maintenance, repair and replacement strategies for the structure and its components to ensure
functionality over the design life of the structure.
Components whose predicted service life is less than the design life of the structure shall be inspectable and
replaceable.
In the event of renovation, the design life of the revised structure shall be reconsidered.
In the event of repairs necessary to correct damage or premature deterioration, the repairs shall be designed,
constructed and maintained to provide the required performance over the design life agreed upon between the
owner and the designer.
7.2 Formats for checking durability
7.2.1 General
The basic durability requirement formulated in 7.1 shall be checked in one of the following two ways:
⎯ by the service-life format in 7.2.2;
⎯ by the limit-states format in 7.2.3.
7.2.2 Service-life format
The service-life format consists in specifying the design life, t , of the component or structure in accordance
D
with Clause 8, and in determining the predicted service life, t , of the component or structure in accordance

SP
with Clause 9 for a target reliability selected in accordance with 8.6.
For service-life prediction based on data from experience and tests (e.g. the factor method in 9.3.2.4), the
basic requirement of 7.1 is given by Equation (1) with t = t .
S SP
For a service-life prediction based on the limit-states method using the probabilistic format in 9.3.2.2, the basic
requirement of 7.1 is as given in Equation (3):
P(t u t ) u P (3)
S D target
where the service life, t , is modelled mathematically as a function of basic variables X , Y and time t, where X
S i i i
is a function of agent transfer for t in Equation (2), and Y is a function of damage or resistance for t
start i exposed
in Equation (2). See Figure 2 and Clause A.3.
Alternatively, this limit state can also be checked using a partial factor format (see also 9.3.2.3):
t /γ W t and γ W 1,0 (4)
Sk S D S
where
t is the characteristic value of t as defined in 3.5;
Sk S
γ is a partial factor calibrated in accordance with ISO 2394 to satisfy Equation (3).
S
7.2.3 Limit-states format
7.2.3.1 Ultimate limit state
The basic requirement for the ultimate limit state (ULS) defined in 6.6.1 at any time, t, during the design life of
the component, t , is given by Equation (5):
D
R(t) W S(t) (5)
where
R(t) is the resistance capacity of the structural component at time t;
S(t) represents the action effect (e.g. an internal force or stress) at any time t.
8 © ISO 2008 – All rights reserved

R(t) and S(t) are modelled mathematically as a function of the basic variables, X , Y and t, in accordance with
i i
ISO 2394. The ULS condition given in Equation (5) is ensured by checking that, at any time t, the conditions in
Equation (6) hold:
P (t) = P[R(t) − S(t) < 0] < P (6)
f target,ULS
R(t) and S(t) are depicted in Figure 2. The probability of failure, P , is indicated in Figure 2 as the region below
f
the horizontal axis for time t. This probability should not exceed P , as determined in accordance with
target,ULS
8.6 (see Figure 2).
7.2.3.2 Serviceability limit states
The basic requirement for the serviceability limit states (SLS) defined in 6.6.2 at any time, t, during the design
life of the component, t , is given by Equation (7):
D
S > S(t) (7)
lim
where
S(t) is the action effect (e.g. a stress or deformation) at any time t;
S is the serviceability limit (see Figure A.6).
lim
S(t) is modelled mathematically as a function of basic variables, X , Y and t, causing damage or loss of
i i
appearance. The SLS condition in Equation (7) is ensured by checking that the conditions in Equation (8)
hold:
P (t) = P[S − S(t) < 0] < P (8)
f lim target,SLS
In practice the limit state conditions in Equations (5) and (7) can also be checked using a properly calibrated,
partial factor design check format as described in ISO 2394. Equations (6) and (8) serve as the basis for
calibrating partial factor design check equations associated with Equations (5) and (7).
NOTE Figure 2 shows the service life, t , as a random variable having its own cumulative probability function as
S
indicated below the horizontal axis in Figure 2. The service life can be found as the time at which R no longer exceeds S
for the ULS, or S no longer exceeds S for the SLS. In the case of cumulative probability functions as shown in Figure 2,
lim
there is a one-to-one correspondence between the basic durability requirement embodied in the service-life format,
Equation (3), and the limit state format, Equations (6) and (8). This applies to material deterioration and to material
deformation that is cumulative. For cyclic material deformation due, for example, to annual cyclic moisture or temperature
changes, the limit-states format in ISO 2394 is recommended. The effect of interventions, such as protective treatment of
wood during the service life, is indicated in Figure 3 (see also Clause A.2 for a case regarding a timber power pole).
7.2.3.3 Initiation limit state
The basic requirement for the initiation limit state can be evaluated in accordance with 7.2.3.1 or 7.2.3.2 by
assuming that t (Y ,t) = 0. See Clause A.3.
exposure i
7.2.4 System durability versus component durability
The limit state analysis for durability using Equations (1), (2), (5) or (7), is equally applicable to structural
systems as to the individual components of a structural system. If a system can be described in terms of a
well-defined, logical assembly of components, then systems analysis, such as fault-tree or cause-tree
analysis, can be applied to determine the durability of the system.
Key
1 probability density function of R(t)
2 probability density function of S(t)
Figure 2 — Mathematical model for predicting service life

Key
1 interventions
Figure 3 — Model for predicting service life, taking into account interventions

10 © ISO 2008 – All rights reserved

8 Design life of a structure and its components, t
D
8.1 Structure
The design life of a structure should be agreed with the client and the appropriate authority. Typical design life
categories for structures are given in ISO 2394:1998, Table 1.
8.2 Components
The design life of a component should be determined considering
⎯ the design life of the structure,
⎯ exposure conditions (environmental action),
⎯ difficulty and cost of maintenance or replacement, taking into account its accessibility,
⎯ the consequences of failure of the component in terms of costs of repair, disruption and operation, and
the hazard to users or others (see Table 1),
⎯ current and future availability of suitable components,
⎯ technical or functional obsolescence.
8.3 Component service life related to the design life of the structure
Permanent components (foundations and main structural members) should be expected to perform for the
design life of the structure with a high reliability (low probability of failure). Components whose design life is
less than that of the structure (or an assembly of components of a structure) should be designed to be
accessible to allow inspection, repair or replacement, as well as the maintenance requirements. A rational,
long-term plan for maintenance of the structure and its components, including planned repair and
replacement, should be set up as recommended in Clause 10.
8.4 Difficulty and cost of maintenance or replacement
Individual components can be classified into categories of maintenance (for example “little or none”,
“significant” or “extensive”) by considering costs, extent and frequency of disruption for users (e.g. access).
The selection or design of components and the specification of the necessary maintenance should be
determined by life-cycle cost (including user cost) for economy or life-cycle assessment for sustainability. To
extend the service life, inherent superior durability or implementation of a more comprehensive maintenance
programme, or both, should be specified.
NOTE 1 Methods of life-cycle cost (for economy) are provided in ISO 15686-5.
NOTE 2 Methods of life-cycle assessment (for sustainability) are provided in ISO 15686-6.
8.5 Consequences of failure
Table 1 identifies four categories of failure. Components whose failure threatens life or health or causes major
disruption should be designed to provide a greater reliability during the design life than those whose failure
does not threaten life or health or cause major disruption.
8.6 Selection of target reliability
Reliability of the durability of the structure and of each component shall be chosen based on the design life of
the structure, the component design life related to the design life of the structure and the difficulty and
expense of maintenance and consequences of failure, as given in 8.2 to 8.5. The serviceability criteria and the
appropriate level of reliability should be agreed with the client and the appropriate authority.
NOTE Recommended target reliabilities (expressed in terms of the reliability index, β) are provided in
ISO 2394:1998, Table E.2.
Table 1 — Categories of component failure
Category Consequences of failure Examples
1 Minor and repairable damage, no injuries Components where replacement after failure is planned for, or
to people where other reasons for replacement are more relevant, like
coatings or sealants
2 Minor injuries or little disruption of the Replaceable but important components for the function of the
use and occupancy of the structure, structure, such as installations for heating, lighting and
including components that protect other ventilation or windows, whose replacement is planned before
components essential for the function of failure
the assembly
3 Non-serious injuries or moderate Non-heavy, non-structural components of the facility requiring
economic, social or environmental major repair work if they fail, such as plumbing, or
consequences components/systems whose replacement is planned before
failure, such as structural bearings and railings or cladding
4 Loss of human life or serious injuries, or Structural components that are parts of the primary or
considerable economic, social or secondary load-carrying system, emergency exits or
environmental consequences components causing major damage if they fail (e.g. heavy
parts of the envelope, prefabricated wall elements, heavy
inner walls, etc.)
9 Predicted service life, t
SP
9.1 General
9.1.1 The predicted service life of the components or the structure as a whole shall be assessed taking into
account
a) experience in accordance with 9.2,
b) modelling in accordance with 9.3,
c) testing in accordance with 9.4.
All methods used to determine predicted service life should be based on a sound understanding of building
science principles in accordance with Figure 1.
9.1.2 For the prediction of service life of any component of the structure,
a) experience may be applied where identical assemblies have been used successfully and in the same
environments,
b) modelling and experience should be applied where
⎯ a similar component or assembly has been used successfully in the same environments, or
⎯ proven components or assemblies have been used successfully, but in moderately different
environments,
c) modelling and testing should be applied where
⎯ innovative components and assemblies are going to be used, or
⎯ proven components or assemblies are going to be used in significantly different environments.
12 © ISO 2008 – All rights reserved

9.1.3 The degree to which an assembly or its components are innovative, or the service life is dissimilar to
the one previously experienced, should be established by the application of building science principles as
described in Figure 1.
NOTE 1 The predicted service life of any component of the structure is approximate, based on the environmental
action, damage, loss of resistance or unacceptable appearance assumed in the design, and on construction and
maintenance procedures.
NOTE 2 Service-life prediction of products used in buildings and construction works based on experience and testing
are provided in ISO 15686 (all parts). Service-life prediction of structures based on modelling durability, using conceptual
or mathematical models in addition to experience and testing, are provided in this International Standard.
NOTE 3 Prescriptive requirements for durability of specific components are contained in current codes and standards
and other sources. These requirements usually imply service lives of components which are consistent with current
expectations and which may be considered appropriate for structures of medium or long design life.
9.2 Prediction based on experience
Procedures on the collection and use of data based on experience, by means of inspection of facilities, are
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contained in ISO 15686-2 .
Properly documented local experience, because it is based on reality, provides the most reliable information
for traditional proven components and assemblies. Also, properly documented new experience of unexpected
failures that occur as a result of innovation without adequate research is especially important to control future
failures. Table D.1, for example, is based on experience as well as research. For innovative components and
assemblies, or where non-traditional components and assemblies known to be effective in one environment
are used in a significantly different environment, experience cannot be relied upon; testing and modelling
(research) are also necessary.
9.3 Prediction based on modelling
9.3.1 Conceptual modelling
Conceptual modelling in the design for durability is the application of building science principles in accordance
with Figure 1 and Annexes B, C and D. This applies to the structure environment, transfer mechanisms,
environmental action, and action effects leading to failure. An example of application of conceptual modelling
in accordance with building science principles (Figure 1) for the design for durability is provided in Clause A.1.
9.3.2 Mathematical modelling
9.3.2.1 General
Specific models are material-dependent and, therefore, belong to material design standards.
9.3.2.2 Probabilistic format
Following the selection of target failure probabilities in accordance with the consequences of component
failure (see 8.5) for the limit states in 6.6, a structural-reliability analysis can be performed to check if either
Equations (2) and (3) or Equations (6) or (8) are satisfied. Guidance is given in ISO 2394. See Clauses A.2
and A.3.
9.3.2.3 Partial factor format
Durability can be verified by checking if specific design check equations are satisfied. Equation (4) can be
used to check if the factored characteristic service life exceeds the design life. The factor γ in Equation (4) is
S
calibrated in such a way that Equation (3) is satisfied. Guidance about partial factors and calibration can be
found in ISO 2394.
9.3.2.4 Factor method
An empirical calculation method for estimating service life is described in ISO 15686-8. The factor method is
based on the reference service life obtained through experience and testing under specified conditions. Seven
factors (component quality, design details, site work, indoor environment, outdoor environment, use conditions
and maintenance) are chosen for the particular application and location, multiplied together to give γ in
S
Equation (4), and applied to a reference service life, t , to estimate a characteristic service life, t . The
ref Sk
predicted service life, t , can then be estimated by Equation (4) (see 7.2.2).
SP
[19]
NOTE See ISO 15686-8 for alternative formats for the factor method and for the application of the factor method.
9.4 Prediction based on testing
Testing of components or assemblies is carried out to estimate the predicted service life, t caused by
SP,
mechanisms that occur at t
...