A functional cost approach in the development and use of a project budget cost limit estimator (PBCLE) for capitol building works

The concept of functional cost allocation is not new having been considered in the 1960s and 70s under the title of spatial costing (Ferry and Brandon, 1980). The concept was sound; however, the difficulty was that the allocation of cost to functional (spatial) units (eg rooms) was expensive in preparing a detailed cost analysis on a function cost basis. Ferry and Brandon (1980) stated "Computer models which symbolise a particular building ... are more likely to provide a better solution in the future". This paper will describe a system developed for a major public 'agency' client in Scotland, charged with the responsibility for the provision and operation of specialist buildings. The paper will develop the concept of functional analysis and describe the work undertaken within the Department of Building and Surveying at Napier University, Edinburgh. This work has resulted in the design of a cost limit estimator based upon the concept of functional cost. It is based upon two projects which were commissioned by a public sector client to design a cost limit estimator for defined construction schemes. The projects were organised in two phases and resulted in development of a: 1. function-based cost model and alpha spreadsheet (completed in February 1995); 2. computer-based estimating system (completed in January 1996). Having designed and developed the system, the client is at present using the software (the Project Budget Cost Limit Estimator [PBCLE]). Over the next twelve months the results from its use will be utilised in refining the cost model built into the system. Initial tests of the system have shown its accuracy in calculating the cost limit for a scheme to be within acceptable tolerances for the client. Further validation on its accuracy will be carried out over the next twelve months.