Estimating the Life Expectancies of Building Component

Structural Survey Estimating the life expectancies of building components in life-cycle costing calculations Allan Ashworth Ashworth

Ar t ic l e in fo rm ati on : To cite this document: Allan Ashworth, Ashworth, (1996),"Estimating (1996),"Estimating the life expectancies expectancies of building building components components in life-cycle costing costing calculations", calculations", Structural Structural Survey, Vol. 14 Iss 2 pp. 4 - 8 Permanent link to this document: http://dx.doi.org/10.1108/02630809610122730 Downloaded on: 16 June 2015, At: 01:02 (PT) References: this document contains references to 6 other documents. To copy this document: permissions@emeraldinsigh [email protected] t.com The fulltext of this document has been downloaded 2019 times since 2006*

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Eric Korpi, Timo Ala-Risku, (2008),"Life cycle costing: a review of published case studies", Managerial Auditing Journal, Vol. 23 Iss 3 pp. 240-261 http://dx.doi.org/10.1108/02686900810857703 Anni Lindholm, Lindholm, Petri Suomala, Suomala, (2007),"Learn (2007),"Learning ing by costing: costing: Sharpening Sharpening cost image through life life cycle costing?", International Journal of Productivity and Performance Management, Vol. 56 Iss 8 pp. 651-672 http:// dx.doi.org/10.1108/17410400710832985 George Norman, (1990),"Life cycle costing", Property Management, Vol. 8 Iss 4 pp. 344-356 http://dx.doi.org/10.1108/ EUM0000000003380

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Introduction

Est ima t ing the lif e expe ct ancies of building com pone nt s in life -cycle cost ing calculat ions

Estimates of the life expectancies of building components result in different answers depending on the purpose required. I n theory, many of the components used in buildings are capable of lasting for a very long time. Evidence exists in many very old buildings where an original component continues to provide a satisfactory performance. H owever, in practice, the life expectancy of building components is frequently much shorter for a variety of different reasons. Obsolescence that eventually occurs both in the design and the technology are perhaps the main reasons why generally sound components are removed and replaced. In other situations components decay, are damaged or disused. While reliance may be placed on actual recorded performance data for the life expectancies of building components, it has been shown that such data are frequently subject to a lack of data characteristics. Without this information their value is limited. T hese characteristics include the maintenance policies being applied, the data classification, causes of component failure, the useof non-identical replacements, time-lag delays, hidden costs, timing distortions and the effects of delayed work. Even where these characteristics are known there is still the difficulty of applying the derived life expectancies to new situations for new pro jects. Such lifeexpectancies form an integral part of a life cycle costing calculation.

A llan A shworth

) T P ( 5 1 0 2 e n u J 6 1 2 0 : 1 0 t A A Y A L A M F O Y T I S R E V I N U y b d e d a o l n w o D

The author Allan Ashwort h is Head of Division of Surveying , School of t he Built Environment, N ene College of Higher Education, Northampton, UK. Abstract Considers how t he life expectancies of building components in a life cycle cost calculation can be d etermined. M akes comparisons w ith init ial capital cost estimating, w here forecasts or estimates of cost have b een carried out for m any years. By definitio n an estimat e is unlikely to be spot-on. Also recognizes that life expectancy is not just a math ematical calculation but also requires the use of expert judgement. Any forecast of a future event, while utilizing previously recorded performance data w ill always be infl uenced by prevailing condition s and future expectations. The initial qualit y and standards of the building project are importan t characteristics in determining component life expectancy as is the type of p roject itself. Identifi es a range of different sources of pub lished informatio n on build ing compo nent life expectancies. Different techniques are also discussed that have a pot ential in assisting w ith the prediction of t he lives of building components.

Init ial capit al costing Estimating the capital costs of new building projects requires, among other factors, a combination of knowledge, skill, experience and judgement[1]. T he knowledge component relies on an availability and analysis of previously recorded cost information. In professional practice, this cost information may have been gathered from a surveyor’s own records, building price books or other sources of information such as BCIS (Building Cost Information Service). H owever, these secondary sources of information are used only in those circumstances where personal cost information does not exist, or where it is necessary to validate this information.

Structural Survey Volume 14 · Number 2 · 1996 · pp. 4–8 © M CB Un iv ersi ty Press · I SSN 26 63 -0 80 X

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Estimating the life expectancies of building components

Structural Survey

Allan Ashw orth

Volume 14 · Number 2 · 1996 · 4–8

Building contractors supposedly rely on feedback data from actual building operations on site. T he process which they use is illustrated in Figure 1. All building contractors have their own standard outputs and cost data that are adjusted, usually, subjectively to take into account the peculiar nature of each individual building project. H owever, in practice, estimators make only limited use of previously recorded site feedback, preferring to rely on their own established data, experience and intuition when attempting to forecast future building costs.

in use. T he main purpose of a life cycle cost estimate is in helping to select the best option from a number of competing proposals. H owever there is, as yet, little evidence to support the view that previous life cycle costs have produced reliable forecasts. I n fact when attempting to estimate so far into the future, there is a good possibility that the forecast will be incorrect, bearing in mind the time scale involved. Also the estimated values in a life cycle cost may bear little resemblance to the actual values if these are ever measured.

Chara cteristics of t he prop osed building Figure 1 Site feedb ack process


Constructing a building to a high quality initially supposes that costs in use may then be Estimate reduced. For example, using hardwood windows in preference to standard softwood windows should ensure that the windows will have a longer life expectancy. H owever, a high Feedback Im plem ent quality building might also require higher costs in use in order to maintain its high quality in use and aesthetics. Monitor H owever, in principle, where a building has used a specification requiring the useof good quality materials and a high standard of workSite feedback for an individual project is but manship, these should, under comparative a single sample of data and as such may be conditions, allow for lower sums to be an unreliable predictor of building costs expended on future costs in use. I n addition generally. T here are many examples of to the specification it is also important to identical projects being constructed with examine the design and detailing of the buildvarying total costs and substantial differences ing project to ensure that these conform to between the individual elements that make up sound constructional practice. All too frethe cost. Also the recording of site informaquently poor detailing is repeated, often on a tion is sometimes poor, relies heavily on good large scale. T he type of project being analysed site organization, the skills of the actual opera- is also important since different project types tives, the lack of interference from the client have in themselves different project life and designers, weather conditions and the cycles which in turn influence thelife other vagaries of actual site conditions. Such expectancy of their various components. information has little repeatable value and is A further issue to consider is the way therefore only used where new technologies in which the project is proposed to be or new methods of working are adopted. maintenance managed throughout its life. A further factor which needs to be consid- T his is very much a key issuefor lifecycle ered is that estimating the initial capital costs costing. Buildings that are allowed to go into of new building projects has been carried out disrepair before any work is carried out will for a very long time and as such includes a result in different life cycle cost profiles than substantial base of expertise, knowledge buildings that are managed optimally in terms and practice. of their maintenance and improvements. I n practice, when a building owner’s funds are limited, it is often the amounts that are spent Life cycle cost a naly sis on building maintenance that suffer a reduc T he importance of any estimateis the consistion in their budgets. F or example, the tency and reliability of the forecasts. All life repainting cycles of school buildings are cycle cost calculations require a consideration frequently extended beyond that originally both of the initial costs and the future costs envisaged at the inception of the project. T his 5

Estimating the life expectancies of building compon ents

Structural Survey

Allan Ashworth

Volume 14 · Number 2 · 1996 · 4–8

has an effect not only on the painting costs in use, but maintenance work of this kind often reveals defects that need to be rectified before they deteriorate further. I t is thus seen as a form of preventive maintenance where it is carried out at the specified time intervals. Such delays are likely to have consequences on the life expectancies of the building components that are directly affected. T hepreparation of a lifecycle cost is based on specific assumptions, at or prior to the final design of the building project, that may later be shown to have been false assumptions.

expectancies depending on whether the physical, economic, functional, technological or social and legal obsolescence is the paramount factor influencing their life. For example, the rapid advancements in fuel technology can mean that it is economically (and environmentally) sensible to replace a central heating boiler, even though it is capable of providing a good service for a much longer life. I ts life expectancy is curtailed by its having reached technical obsolescence. An important and useful source of data for those involved in life cycle costing is their own accumulated research and expertise. In the absence of this, one or more of the sources of information identified above could be used. Another source of information is Life [6]. T his Expectancies of Bui ldi ng Components represents the findings from a survey of building surveyors. T he information typically is represented in the format shown in F igure 2. It provides an indication of the sample size and the estimated component life in years using a variety of statistical measures. It can be observed from thesedata, that the life expectancy of softwood windows and doors can vary between one and 150 years. Typically, it represents a life expectancy of about 30 years. F urthermore, it would be foolish, for example, to prepare a life cycle cost based on 150 years, even where guaranteed maintenance is promised, owing to the possibility of advancing obsolescence in buildings as identified above. Changes in use, the implications of fashion and the development of new technologies will also have some impact on life expectancies. T he important message from investment analysts that “past

Building component life ex pectancy data ) T P ( 5 1 0 2 e n u J 6 1 2 0 : 1 0 t A A Y A L A M F O Y T I S R E V I N U y b d e d a o l n w o D

T here is a variety of sources of published information and data on the life expectancy of the different building components. T hese include the manufacturers, Building M aintenance Information (BM I)[2], the former National Building Agency (N BA)[3], the Housing Association Property M anual (H APM )[4], the former Property Services Agency (PSA)[5] and the Building Research Establishment (BRE)[6]. Some of these sources emphasize the longevity of some building components. It can be argued that if a building is properly designed and constructed then it can be maintained almost indefinitely. T here are many examples in buildings where the original components remain in use for hundreds of years. H owever, for the purpose of life cycle costing it is not so much a question of “how long will a component last?” but “how long will a component be retained?” All components have widely different life

Figure 2 Life expectancies of softw ood w indow s Window s and doors: softw ood – painted Number

Num ber of replies 66

20 Estim ated life in years M edian M ean SD M inim um M axim um

30 32 22 1 150

15 10 5 0

0

20

Time in years

6

40

60

80

100

120


Estimating the life expectancies of building components

Structural Survey

Allan Ashw orth

Volume 14 · Number 2 · 1996 · 4–8

performance is no guarantee of future projections” can be applied so easily to building life cycles and the forecast of building component lives. A further analysis of the data shown in Figure 2 is provided in Table I. T his combines three separate charts from the RI CS/BRE survey[6].T his indicates that 14 per cent of the respondents to the survey expected softwood windows to last less than ten years, almost 40 per cent to last for less than 20 years and over 70 per cent for no longer than 30 years. T he survey does not providean indication of the possible reasons for the expected different life expectancies. T he replacement of the windows may be due to general decay, vandalism, fashion, the installation of double glazing in order to reduce long-term maintenance, development of new technologies, etc. T hese and other data characteristics are not provided. I f this information were included, then the range of values under a particular set of circumstances would be reduced. T his would then allow its reuse in new situations to be made with greater confidence. On the basis of this and other information alone, it is not possible to select a precise life expectancy for a particular building component. T he use of the following technique can be used to test the effects of best, worst, typical and any other scenario in terms of assessing the life expectancy.

may have been introduced. One way of testing whether the results of the life cycle cost analysis are appropriate is to repeat the calculations by changing the values that have been attributed to the individual variables. T his is described as sensitivity analysis. In the caseof building component life, these can be revised easily by using a suitable computer packageor by using a spreadsheet. It is therefore possible to test the effect on the life cycle cost calculations of any building component life expectancy against that which has been included in the analysis as the most appropriatecomponent life. It needs to be remembered that life cycle costing is a technique to assist in the selection of the best or most economic of the alternatives that are available. Sensitivity analysis will not do this for us, but it will provide us with a range of different values that can be used to help to formulate overall judgements.

Othe r te chniques to consider It is also worth noting two other methods or techniques that can help to select the most appropriate life expectancies for the different components in the building that is being life cycle costed. T hefirst of these is called M onte Carlo simulation and is based on the general idea of using sampling to estimate the desired results. T he sampling process requires the description of the problem under study by an appropriate probability distribution from which sample values are then drawn. T he forecasting of building component life expectancies is an ideal problem for simulation. Simulation is simply a means of creating a typical representation of the system being studied. I n order to do this it is necessary to know the detailed characteristics and the

Use of sensitivit y ana lysis During a life cycle cost analysis a large number of different assumptions need to be made, such as the lives of the different building components. I t is necessary to test these assumptions in order to reduce any possible distortions or misleading information that

Table I Life expectancies of softw ood w indow s: percentage distribution o f respondents

Life expectancy (years) 0-10 11-20 21-30 31-40 40+

Painted (% )

M icroporous paint ed (% )

Stained a nd varnished (% )

Tot als (% )

11 24 33 17 15

17 25 28 15 15

15 28 30 10 17

14 25 31 14 16

100

100

100

100

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Estimating the life expectancies of building compon ents

Structural Survey

Allan Ashworth

Volume 14 · Number 2 · 1996 · 4–8

relevant measures to be applied in order that sampling from a probability distribution can take place. A second method is to develop and use an intelligent knowledge based system (I K BS), sometimes colloquially referred to as an expert system. T hese are systems that behave like experts. T hey do not necessarily break any new ground, but pick the brains of a group of experts, who already have the knowhow to solve a particular problem. T he rules that an individual uses are stored carefully in the computer’s memory and recalled in much the same way that an expert arrives at a decision. T he construction and property industries already use a number of expert systems software, that have developed to assist practitioners in their work. I n the context of building component life expectancies, a series of question sets would be displayed on the computer monitor to be answered by the user. Where answers could not be provided then the expert system would make assumptions depending on the other answers provided and the information retained in the expert system program.

• • •

•

• •

• • •

Conclusions

for the same building component in the same situation and under the same circumstances. Assess the initial quality and standards of the building being constructed. Assess the design and detailing of the different components. Consider ways of improving the design in order to reduce defects and encourage component longevity where this is desirable. Examine the different sources of information on component life expectancies in addition to using personal data. Relatethe data and other information to the particular project and client type. Assess management policies recognizing that these may also change many times during a project’s life. Apply sensitivity analysis to the results. Consider theuse of simulation or expert systems. U se acombination of objective analysis and subjective judgements to determine the life expectancies of the different building components.

References

L ife cycle costing requires many different variables to be assessed, usually over considerable periods of time into the future. T he estimation of life expectancies of the different building components are just one of these variables. T here are wide variations in the life expectancies of building component data from practice. T his makes the estimating of values uncertain and difficult to predict. I t can never be precise due to the many vagaries associated with design, construction, use and management of buildings. T he following process should assist the practitioner: • Recognize that, in practice there is a wide variation in life expectancy values even

1 Ashworth, A. and Skitmore, R.M., Accuracy in Estimat- in g , Chartered Institute of Building, Occasional Paper No. 27, 1977. 2 BM I, Occupancy Cost Planning , Building Maintenance Informat ion Service, 1992. 3 NBA, Maintenance Cycles Life Expectancies , National Building A gency, 1985. 4 HAPM , Component Life Manual , E. & F.N. Spon , London, 1992. 5 Property Services Agency, Costs in Use Tables , HM SO, 1991. 6 RICS/BRE, Life Expectancies of Building Components: Preliminary Results from Survey of Building Surveyors’ Views , Royal Institution of Chartered Surveyors Research Papers, No. 1 1, 19 92.

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Estimating the Life Expectancies of Building Component

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