The factors relevant to the selection of an appropriate method of evaluation are explored. This involves the initial categorisation of the various types of claims for overheads, such as original and further overheads. The particular or distinguishing features of these different types of claims assume importance, as does a proper understanding of the factors relevant to their proof and evaluation, and the extent to which in any given case such factors may appropriately be emphasised or relaxed.

The law has tended to side with the accountant’s approach to overheads, including its readiness to adopt conventions such as allocation and absorption costing. This can, for example, be seen in the various methods commonly used in the evaluation of further overheads claims, particularly the time-based appraisal methods. These and other methods—such as those based on volume considerations—are explored and their merits investigated, including the relevance to any such investigation of the principles of other disciplines, particularly economics.

The associated literature on the evaluation of construction overheads claims demonstrates a marked degree of inconsistency and confusion not only in relation to these areas but also over the legal principles which are relevant to the different types of overheads claims or to the components of their appraisal, what should be proved and in what circumstances such requirements might be relaxed, where the burden of proof lies with any component of the appraisal and why, mitigation, and equivalence.

Finally, the importance of duplication is explored, as is the validity of the methods commonly used to identify and remove that duplication in relation, in particular, to varied work.