Standards for design life of buildings: utilization in the design process

Construction

and Buil&ng Materials, Vol. 10, No. I, pp. 487490, 1996 Copyright la 1996 Elsevier Science Ltd All rights reserved 095&0618/96$lS.OO+O.OO

Printed in Great Britain.

PII:SO!HJ-O618(96)OOO18-9

ELSEVIER

Standards for design life of buildings: utilization in the design process G. Soronis Building Standards Received

Institution,

1 December

BST, Stockholm,

Sweden

1995; revised 3 June 1996; accepted 3 June 1996

Durability is an integral part of modern building design. To meet this issue many national standards have been developed, principally to assist the communication of information of design life and durability between the parties involved in a building product, i.e. clients, designers, manufacturers, contractors and specialists. In particular those standards are intended to discourage unrealistic expectations of the service life of buildings and parts of buildings. This paper contains a state of the art review of national standards and principal guides in the UK, Japan and Canada. It also outlines the first draft of an international standard in service life planning of buildings and gives recommendations for its further development. Finally, this paper presents issues concerning the implementation of the standards. Copyright 0 1996 Elsevier Science Ltd. Keywords:

durability; service life; standards

management plan. Thus, standardization work is not based on pure scientific knowledge alone, but also on empirical knowledge. Many countries have developed national standards and guides to facilitate the service life planning of buildings. The International Standards Organization (ISO) has also focused this area and in 1994 initiated the IS0 TC 59/SC 3/WG 9 group which aims to the development of international standards and guidelines for the service life planning of buildings.

Recent attention world-wide has highlighted the need for the construction industry to cut its costs significantly and to improve its effectiveness. For example in the UK a figure of 30% has been proposed by a joint government/industry review. Such savings can only be achieved by significant improvements in current practice. One such improvement would be the ability to design buildings for a specified design life’. The European Construction Products Directive in force in the EU and most EFTA states sets out six essential requirements for works which must be satisfied during an economically reasonable working life2. It has created a regulatory framework in which working life and durability aspects of products find an important place. Technical specifications for building products prepared by CEN and EOTA must contain provisions for assessing the product durability. Building design always begins with a pre-planning process which includes the selection of materials and the determination of their relative positions in a construction to produce a building or a part of a building. Considerations on durability in building design, demand extensive knowledge and understanding of the service life of materials in their in-service environment3. Thus, there is a great need for standards to address the issue of durability in building design. This is a large and significant task which requires that durability information is available to designers in a readily usable format, compatible to other design tools. The objective of the standards is to set out a procedure for designing buildings for a specific service life. This service life is expected to be achieved without major problems, if it is maintained according to the proposed maintenance

Aims The purpose of the work presented here is to: l

l

l

To give a state-of-the-art review on the existing national standards and guides for service life planning of buildings. To outline the current work for the development of an international standard for service life planning of buildings. To give recommendations for further development and implementation of these standards.

State of the art review in national standards and guides

British Standurd

BS7543

The expression of durability in BS7543, ‘Guide to Durability of Buildings and Building Elements, Products and Components’4, is provided by detailed definitions of the terms for Service Life, Required 487

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Service Life, Predicted Service Life and Design Life. The durability limit is also discussed in relation to potential problems or unclear definition of the acceptable level of deterioration and attention is drawn to areas in which misunderstanding is more likely, The service life is taken as the period to the point at which performance deteriorates to an ‘agreed’ or ‘defined’ unacceptable level. The required service life is that which meets the users’ requirements and is usually the same as the client’s brief. The predicted service life is an estimate of service life derived from previous experience, from extrapolation from short term or accelerated test results. The methodology proposed for predicting service life of building materials and components follows the principles as described by Masters and Brand?. The design life is intended by the designer in discussion with the client and aims to support the client’s performance specifications. Recommendations for the design life of buildings are given (< 10 yrs, > 10 yrs, >30 yrs, >60 yrs, > 120 yrs). The building components or assemblies are divided in three levels: replaceable, maintainable or lifelong, plus the level of maintenance required. The standard gives a categorization of the effects of failure in building assemblies and components from A-H. Categories A-D denote failure connected with danger to life and health. Categories E-H denote failures connected only with non-human impacts and mostly connected with economic considerations. A systematic design life data sheet is also described. This should be filled in by the designer during the briefing and early design stages of a building project, to record proposals for the durability of the building and its parts. This will provide a statement of the designer’s intentions that can be used for discussions with the client which have the aim of reaching an accord on detailed design and specification. It should also alert the client to the need for maintenance and replacement of parts of the building during its entire design life. The Cunadian Standurd

S478

The expression of durability in S478, ‘Guideline on Durability in Buildings’6, is provided by detailed definitions of the terms for Service Life, Predicted Service Life and Design Service Life. The Guide provides a framework for durability targets and suggests criteria for specifying the durability performance of buildings in terms that are commonly used, but were previously undefined. The service life is taken as the actual period during which the building or any of its components performs without unforeseen costs or disruption for maintenance and repair. The predicted service life is defined as the service life predicted from recorded performance, previous experience, tests, or modelling. No specific methodology is recommended for service life predictions of building materials and components. The design service life is defined as the service life specified by the designer in

life of buildings:

G. Soronis

accordance with the expectations (or requirements) of the owner of the building. Recommendations for the design service life of buildings are given (~10 yrs, 10-24 yrs, 25-49 yrs, 50-99 yrs, ‘100 yrs). Durability and quality assurance are emphasized as an essential consideration in every stage in the design service life of any building as, for example, the stages of Conception, Design (detail, specifications), Tendering, Construction, Handover, Operation and Maintenance, and Renovation. When determining the design service life for building components, it is suggested that at least three categories be used to describe necessary maintenance: little or none, significant and excessive. The standard gives a categorization (l-8) of the effects of failure defined by the worst consequence of a failure in that category. Categories l-5 denote failures connected only with nonhuman impacts and mostly connected with economic considerations. Categories 6-8 denote failure connected with danger to life and health. A systematic building design data sheet is given. Its intended function is to document the basic requirements for the building and the design variables the designer will need to work with, as agreed by the owner. Once completed and accepted by both the designer and the owner the building design data table would normally not be altered unless there is a major alteration in the owner’s requirement for the use, construction or operation of the building. A systematic maintenance guide (to be tilled in by the designer) is given. It is intended to identify explicitly for the owner the extent of maintenance necessary to ensure that design service lives are achieved. The Jupunese

Principul

Guide

In 1993, the Architectural Institute of Japan published the English edition of the ‘Principal Guide for Service Life Planning of Buildings’. In principle the Japanese Guide is similar to the British BS7543 and the Canadian S478 as in much as it requires the Planned Service Life (corresponding to Design Life in BS7543 and Design Service Life in S478) of a building, its components and the maintenance needed to be specified by the designer. However the Japanese guide differs clearly from the other standard documents because it contains distinct formulation of the responsibilities of all people involved with durability in building (these responsibilities have to be specified by the designer). In addition to this the Japanese Guide takes into consideration not only the physical deterioration, but also aspects concerning the flexibility and obsolescence of the building. Thus, the Predicted Service Life has to determined as the smaller value of the predicted values of Service Life obtained on the basis of physical deterioration and obsolescence. Two methodologies are proposed for the prediction of service life. The one is the methodology as proposed by Masters and Brandt’. The other is an empirical factorial approach which is based on a reference value for the predicted service life (mainly based on the locai environment). This reference value has then to be

Standards

for design life of buildings: G. Soronis

adjusted by the designer by using empirical factors concerning the quality of materials used, the design level, the work execution level, etc. The Japanese guide has nine classes with representative values of the planned service life of 3, 6, 10, 15, 25, 40, 60, 100 and 150 yrs. The guide goes beyond BS7543 and S478 by providing recommended classes of planned service life for different structure and building use and for different parts of building elements and components. Two standard specification tables are recommended in the guide. These tables describe the specification of maintenance of parts elements, components and services of buildings which concerns repair, renewal, inspection and care. The HAPM

Component Lije Manuul

One of the few sources to provide quantitative information on the expected service life of building components is the HAPM manual (Housing Association Property Mutual Ltd) in the UK*. This document was written by Construction Audit Limited and published in 1992. Although this document has been prepared specifically for insurance purposes, readers using the data for other purposes may wish to add their own adjustment factors. The guide is mainly intended for domestic dwellings up to three storeys by covering seven primary groups; flooring components, walling and cladding components, roofing components, doors, windows and joinery, mechanical equipment components and external work and outbuildings. The HAPM document is the first document to provide extensive life-span assessments for a wide range of building components which are classified within the concept of quality specifications. Each specification in the document is represented by a coding (A-H) which defines its Insured Life class for >35, 35, 30, 25, 20 and up to 5 yrs. Insured lives are assigned to components on the assumption that a minimum level of maintenance will be carried out. When non-typical or extreme conditions prevail, adjustments factors are provided. These may be negative or positive depending on whether the deviation from the norm is detrimental, or beneficial. Examples of such conditions include marine environments, polluted/industrial atmosphere and frost pockets. General guidelines also include installation in accordance with manufacturers’ direction, good practice, relevant code of practice and British standards and the use of appropriate design details. Data sheets in each component group include a description of each component type, adjustment factors, assumptions, locations, typical maintenance, and specific notes. It is well known that in order to make reliable predictions of service life it is essential to obtain regular feedback from structures. HAPM have automatic feedback via claims (when they are large enough to be of consequence) and hence are in a unique position to be able to update the manual to reflect performance in ser-

489

vice. This makes the HAPM Component Life Manual exceptionally valuable as a source of service life predictions.

International standardization Work within IS0 aims to provide a methodology for assessing whether a particular design can confidently be expected to result in a building which, if built and maintained as intended will achieve the intended life. This work has been much facilitated by the pioneering documents on the same subject in Japan, the UK and Canada as described earlier. A first draft of the standard has been presented in Delft, The Netherlands (in the IS0 TC59/SC3/WG9 meeting), in April 1995’. This document presents the generic principles which can be applied in estimating the expected life of a building of any type to be built in any environment. It can also be applied in estimating the remaining life of an existing building. However, while the principles are generic, tables are provided to help assess the lives of materials and components in a building that may not cover every eventuality. The standard is in five parts. Part I presents general principles for evaluating whether the expected service life will be at least as long as the design life. Part II details the methods to be used in determining the expected life. Part III presents information on quality assurance, maintenance and performance audits. Part IV provides references to relevant standards and other literature, and a glossary. Recognizing that computers will almost always will be used in applying the standard, Part V recommends formats for the data to be used and the reports to be generated. The standard is planned to serve designers, owners, potential buyers/investors, educators, students, etc. and the benefit they should gain from it. It will point out that while it is difficult (sometimes impossible) to make precise estimates of building life, the availability of a standard approach will put estimates on a common basis. The methodology used for the drafting of the standard incorporates all the above mentioned methodologies for national standards and guides into a general generic methodology for assessing whether a building or a building component will perform satisfactorily over its intended life, the Design Life (DL: Design Life of a Building, DLC: Design Life of a Building Component). Thus, the designer has to ensure that the Service Life of the Building (SL) and the Service Life of building components (SLC) are greater than the DL and DLC, respectively. The methodology used for prediction of the service life of the building components follows the Japanese ‘Principal Guide”. That means that the final decision of the service life of the building materials and components is to be taken by the designer whose responsibility is to know precisely all the design parameters. A detailed description of the IS0 work is described in Reference 10.

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Conclusions and recommendations Utilization of standards for service life planning of buildings means that the service life of a building and its components are specified in detail, emphasizing the fact that buildings and building components have a finite life. It also confirms the responsibility of the designer for long term performance and defines the role of the builder, owner, user and maintainer during the entire design life of the building”. The principal barrier to the use of these standards has always been the fact that there are few quantitative methods for reliably predicting the service life of materials and components in a building. To overcome this problem, it is necessary to provide the designer either with quantitative information on the in-service properties of building materials and components or with a method for modelling their performance as a function of time. Of these two approaches, the former is more readily accepted by the designers. For example the HAPM Component Life Manual provides both a user friendly format and substantial information which could form the basis of a manual for design for durability. Results from the latter method could give more accurate information, but they are commonly not used in practical design work. The reason is that this information is fragmentary and not well formulated and mostly available only in scientific publications. In practice where problems must be solved ‘now’, designers do not have the time to study these voluminous documents. However, irrespective of which method is used, it is essential that there is feedback from buildings in use combined with the results of long term performance tests. The prediction of the in-service performance of materials and components becomes more accurate and the safety factors can be reduced. An example of facilities to handle such kind of information is the BRE’s (Building Research Establishment) Defect Database. Another system for monitoring the Performance and Cost-in-Use of Buildings will shortly be available in the form of the Performance and Cost Managed Buildings (PCMB) package. This was developed in the UK under the DoE/SERC Link Programme on Construction Maintenance and Refurbishment by BRE, Ove Arup and the University of Strathclyde. Another important barrier in the utilization of service life information is the development of specification systems to address durability in building design. An example of such a system which could provide a means for incorporating durability/service life information is the British ‘Specification Manager’ package, mainly based on the National Building Specification (NBS). It is therefore crucial for the utilization of the standards to develop integral systems to transfer information from defect, performance and cost management databases to practical building specification for current information on service life, and maintenance requirements.

life of buildings:

G. Soronis

However, the above mentioned system developments are a long term activity. In the shorter term, national and international committees dealing with standardization of service life planning of buildings have the responsibility of planning the implementation of those standards. This can be achieved by: l

0

Encouraging the utilization of empirical values of service life or existing systematic service life information manuals similar to the HAPM Component Life Manual. These values may be conservative, but indicate to the clients that buildings and building components do have a finite service life. Encouraging and initiating research for further development of information which could be directly applied as input to the existing standards.

Acknowledgements I would like to express my deep gratitude to Taywood Engineering Ltd, Building Performance Services and Building Research Establishment for sponsoring my work preparing the first draft of the IS0 standard for service life planning of buildings in autumn 1994. Particularly my thanks go to: l Dr Roger Browne and Dr Phil Bamforth, Taywood Engineering Ltd, UK. l Dr Hywel Davis and Dr Andy Lewry, BRE, UK. l Dr Kathryn Bourke and Mr Paul Wornell, BPS, UK. References I

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2

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S. and Soronis, G. CIB W94 Report 1. In Durubility of

Masters, W.L. and Brandt, E. Systematic methodology vice life prediction of building materials and components. Struct. 1989, 22, 385-392 Guidelines on Durubility

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in

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Principul Guide jiw Service Lijti Plunning of Buildings, English Edition, Architectural Institute of Japan, 1993 The HAPM Component Lijti Munuul, E&FN Spon, London, UK, 1992 Srundurrl /or Service Lijti Plunning of Buildings, Draft I, IS0 TC59ISCIWG9, International Organization for Standardization, 1994 Browne, R.D. and Soronis G. A proposed IS0 Standard for the service life of buildings: Part I, General Principles. In Durubility of Building Stockholm,

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Building Muterids and Components, Proc. Sixth Inr Conf:, Omiyu, Jupun, E&FN Spon, London, UK, 1993 Products und Guide to Durubility of’ Building Elemenh, Componenrs, British Standards Institution, BS 7543, 1992

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Caluwaerts, P., Sjiistrbm, Ch and Haagenrud, S.E. Service life standards - background and relation to the European Construction Products Directive. In Durubilily q/’ Building Muterids und Components, Proc. Sevenrh Int. Slveden, E&FN Spon, London, UK, 1996

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Mureriub und Components. Proc Sevenrh Inr. Conj.‘. Sweden, E&FN Spon, London, UK, 1996 P.B. A Revieiv of 837543, A Guide to Durability of Elements, Producrs und Componenrs, Taywood

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