Risk response

ISO15686-3 deals with quality assurance and auditing of service life. The above comments are a misinterpretation of the ISO 15686-3 as evidenced by Dr Davies in his presentation on Whole Life Costing (see slide 16 http://www.necdm.co.uk/speakers/hywel_davies/whole_life/sld001.htm). In fact, the scope of the document is to serve guidance on service life reviews and performance audits of building components. Examining the standard in greater detail will reveal that the terms ‘whole life cost’ and ‘whole life costing’ can be found only once, on page 10, which refers the reader to the as yet unpublished, ISO 15686-5. The level of detail that Part 3 of the standard pertains to is not appropriate to a text, which focuses upon cost modelling, but it is very relevant to a book on service life prediction. We understand that ISO 15686-5 is going to be about whole life cost models. But, Part 5 is not even published! Hence, we concluded that the reviewer might have confused the subject of whole life costing and service life planning.

The other criticisms in the review focus on the service life prediction aspects of the text. The authors have made reference to EOTA guidance developed on the basis of the service life prediction concepts as expressed in ISO 15686-2 plus other references in the chapter that have reviewed the standard. The overriding aim was to demonstrate that service lives of new and existing structures are a prerequisite for the determination of the replacement frequency of components and the whole life costing analysis period. We believed we achieved this aim with a novel method based on stochastic forecasting of service life of components.

The case study that concludes part two of the book is not about m&e design. It presents an empirical approach to comparing and selecting an alternative ac system based on whole life cycle costing. One should differentiate between the design and optimisation of m&e systems, which this book is not concerned with, and the use of the historical performance data of ac systems for whole life cycle cost calculation. In fact CIBSE TM30 differentiates between the two concepts. TM30 uses two models, the first (an optional generic model) which is used to optimise energy consumption. The output from the energy optimisation is used in the computation of whole life cycle cost. The second model allows the user to define capital and operating costs for whole life cycle cost computation. In fact, the model presented in TM30 uses the same whole life cycle cost centres that are used in our case study, although our model was published far earlier at the 9th International Conference on the Durability of Building materials and Components. Hence, the case study is related to the second model of TM30 not the generic model described. In our judgment the model presented in the case study is far superior to the TM30 whole life cycle cost model, for the reason that whole life costs are uncertain due to their long term projections, which are subject to variation in the attributes as discussed in detail in the book. Hence, stochastic modelling of ac whole life costs is a more appropriate methodology than that presented in TM30.

The reviewer does make a valid point though in that there are a few typographical errors, which the authors acknowledge and take full responsibility for.

Dr A H Boussabaine, School of Architecture, University of Liverpool; Dr RJ Kirkham, School of the Built Environment, Liverpool John Moores University