A novel stay–in–place formwork for vertical walls in residential nZEB developed for the Mediterranean climate: Hygrothermal, energy, comfort and economic analyses

The Stay-in-place (SIP) formworks technique facilitates construction scheduling and labor savings. In continental climates, traditional Insulating Concrete Formworks (ICF) are largely used to limit thermal losses; nevertheless, the internal insulating layer hinders rational exploitation of building inertia to reduce cooling demand when ICFs are used in warm climates. Consequently, novel SIP formworks must be developed to overcome this limitation. In this paper, SIP solutions made of an external insulation layer and a high thermal conductivity internal layer, are proposed and compared with a traditional ICF and brick masonry wall. Energy performances, hygrothermal behavior, thermal comfort, and economic revenues were evaluated regarding two opposite Mediterranean climatic contexts. The dynamic hygrothermal analysis reported a higher water content in SIP walls compared to brick masonry. However, the use of cellular concrete, gypsum fiber, and plasterboard panels on the inner side provided better results than standard ICF. Water content highly affects the U-value of the wall and, during the heating period, a wider variation range was detected compared to the brick wall. Energy simulations performed on a reference building using a steady-state U-value proved that the proposed SIP walls reduce the thermal heating requirement by 9% compared to ICF walls, whereas slight decrements were obtained in comparison with the brick walls. Regarding the indoor operative temperature, assuming a free-running building without air-conditioning, SIP walls with internal gypsum-fiber panels led to higher values in winter and lower in summer. Instead, SIP walls with internal plasterboard panels produced the best cost-effective scenario.