Lifecycle cost analysis of flat roofs of buildings

Flat roofs have had been gaining in popularity in several countries, and the roof is one of the building envelope elements where most thermal exchanges with the exterior occur, and this considerably influences the thermal performance of buildings. There is little international information on the joint thermal and economic performance, on the relevant methods of analysis, or on the comparison of various types of flat-roofing systems. A group of 472 flat roofs were studied, including roofs with limited access, accessible for people, and accessible for vehicles. All the costs associated with the lifecycle of flat roofs were estimated to find the most advantageous solutions in economic and energetic terms. It was found that material acquisition and execution costs are the most determinant; inverted flat roofs with limited accessibility are more economical; lightweight concrete with expanded polystyrene granules used as shaping layer and atactic polypropylene polymer bituminous or polyvinyl chloride thermoplastic membranes are the most economical solutions. The results achieved could help decision makers when selecting the flat-roof system to be used in each building.