Architecture / June 16, 2018 / .
In general it can be said that larger buildings with simple, rectangular, regular floor plans and elevations will be less expensive per sq.m. of floor area than smaller, complex shaped, curved or angular buildings. Economies of scale apportion fixed overheads to a larger extent of productive space. Simple setting out and buildable solutions encourage greater plant use and generate higher productivity and less waste. Complex layouts and details are slower to assemble and may involve a number of trades with a consequent greater risk of mistakes and defects. The degree of compartmentation and repetition will also affect the overall cost of the work. New building work is considerably cheaper than work of a repairing nature or work in existing buildings. Single storey structures tend to be more costly than buildings up to three storeys high, beyond which point they become progressively more expensive.
Clients who prioritise cost over speed or who require fixed price lump sums will generally experience longer development programmes, as designs must be substantially completed before tenders can be obtained. This process may take a considerable amount of time as careful thought is required to develop and refine the scheme design. The design, in turn, influences the contractors construction methods which determine length of time taken to complete the contract on site.
Speedy completion is often required on commercial developments. The pressure to achieve early completion intensifies when financing and interest costs associated with acquiring the site begin to mount. Clients will seek the early appointment of a contractor in these situations to enable a fast start up on site and will favour fast track design approaches where the design is developed in parallel with site construction operations. Such approaches risk allowing insufficient time to identify or consider beneficial design options, and may, on occasion, lead to abortive working and losing time. Speedy construction on site often requires accelerated working and shift or overtime payments, more intense management presence, and the use of dependable subcontractors and suppliers, all of which add to the cost of the project. Fast track approaches rule out cost certainty and the client will become aware of the eventual cost only at an advanced stage of the project.
The choice of the material, and hence the cost, may be influenced by factors other than aesthetic qualities. For example fast-track construction projects may use a steel frame in preference to an in-situ or precast concrete frame in order to reduce overall programme durations. Although the concrete option may be cheaper, the shorter programme achieved by using steel may offset this initial cost advantage. Technical decisions such as these are made for each building element and these have a direct bearing on the eventual cost. Where considerable repetition can be achieved it may prove economical to prefabricate certain structural elements or to standardise various components and fittings.