Impact Factors on the Cost Calculation for Building Services within the Built Environment

Different building epochs, materials and styles challenge planners and furthermore executing companies to define the required services upfront. The presumptions made, often differ from the real conditions on site (building substance), so that additional investigations in advance would be helpful, to gain more knowledge on the existing structure. These deviations then demand additional services on site, which are usually not listed in the bills of quantities and lead to budget overruns. Clients can cushion such overruns through reserves in the budget, but how do contractors deal with those uncertainties in their calculation? To investigate if and how these risks of differing construction and site conditions affect their bids of contractors, quantitative research has been applied and a survey has been conducted. The trend shows, that not the cost component of labour work increases, but is calculated into the prices for materials in order to hide those additional costs. Uncertainties in construction works on existing buildings will always be difficult to evaluate. To minimize the risks of running an unprofitable construction site, employers have the possibility to work with a flexible budget, but contractors can only act to uncertainties and additionally required services with claiming.