The existing methods of evaluating the environmental life cycle assessment (LCA) and life cycle costs (LCC) performance of a building concept have been widely used, since they offer the possibility to consider the system globally and avoid, thus, the hidden impacts. However, many studies have indicated the possible uncertainties of the input parameters and recommended the use of probabilistic methods, to deal with these issues. The current study continues towards this direction and presents a systematic way to take into account the uncertainties of the building elements’ service life within a stochastic framework, by defining the corresponding probability density functions, based on a new service life database. Applying this methodology for the calculation of the LCA & LCC for multifamily houses in Switzerland revealed that the replacement stage contributes with a share of up to 36% on the GHG emissions. Furthermore, through a global sensitivity analysis, the uncertainty on the replacement rate of six building elements was found to mainly influence the LCA & LCC uncertainty, i.e. compact façade (external insulation), windows, roofing, flooring, internal layout and ceiling covering. Finally, it was found that the reference service life of the building significantly influences the LCA and LCC uncertainty. In order to increase the reliability on the building LCA and LCC results, it is recommended to take into account probabilistically the service lives of the building elements, which mostly influence the LCA uncertainty.