Preassembled timber panels for roof retrofit: a method for the selection of sustainable and recycled materials

Because of the sheer size of the building stock in Europe, meeting the goals of energy efficiency and reduced carbon emissions in the future requires radical interventions on existing buildings. Although Europe is facing the most critical economic crisis since the end of the Second World War, and construction is one of the most affected sectors, refurbishment and energy retrofit seem to have a great potential in the economical recovery of the real estate sector in consolidated areas like the EU. In Italy, the share of refurbishment and energy retrofit of existing buildings has considerably risen in the last five years. From a market survey recently carried out, the residential sector seems to be the one able to attract the highest share of resources and investors, with an increasing number of refurbished houses expected in the next 10 years. The same survey analysed also the different components of a building which are expected to account for the highest share of interventions in the next decades. Among all these, the roof seems to have the greatest potential, both because it often requires dismantling and rebuilding to extend the existing building, and because it presents a large amount of thermal energy loss in winter and energy gain in summer, being exposed to the sky vault. This paper focuses on the investigation of the real estate market and on the definition of methodological criteria for the choice of the most sustainable materials to be adopted in the energy retrofit of existing roofs. On the basis of the outcomes achieved within a privately funded research project, the work aims to develop a semi-quantitative matrix to classify and select the best products, components and elements available on the market for that purpose. All the selected materials are the basis for the design of a preassembled timber modular panel to be applied on the roof as a replacement for existing structures. In fact, even if increasing the insulation thickness of a roof is often a simple task, easier than in other parts of the building envelope (i.e. external walls, basement, etc.), there are several benefits in substituting the existing roof with preassembled timber modular panels: an optimization of the duration of on-site work during the construction phase – often a crucial problem especially in some historical Italian centres – a lower cost of on- site installation, a better control of the hygrometric performance of the elements, and generally a better quality of the built asset.