Economic and Sensitivity Analysis of Net Zero Energy Refurbishment of Terraced Houses

Postwar terraced houses, built en masse for the European middle-class, remain a major consumer of energy, significantly affecting the performance and quality of the residential stock. Prêt-à-Loger is a net zero energy refurbishment (NZER) concept addressing 1.4 million postwar Dutch terraced houses and possibly some other 30.6 million spread throughout NorthWestern Europe. By applying an integrated external renovation system living quality and the durability of the house are improved, and extra space is added. This non-invasive renovation project competed at the Solar Decathlon Europe 2014, winning five prizes, among which the first in sustainability. Despite the easy and fast applicability, the financial aspect still presents a serious barrier for large-scale implementation of this and other energy neutral renovation concepts. The research summarised in this paper firstly identifies the economic factors that can boost the investment in energy neutral refurbishments, on the basis of interactions with public and local authorities, private companies, research institutes and end-users. Secondly, it studies the economic potential of the NZER and the relative importance of the identified factors with Monte Carlo simulations. Different cases are considered to address the situation of single homeowners as well as housing associations needing to refurbish multiple dwellings. The increase of total rent after renovation for the housing association case and the energy prices for the homeowner case are the most influential factors together with the capital expenditures; the maintenance cost and increase of property value are also relevant elements that can be affected by the right design choices. For the Prêt-à-Loger solution, for instance, a higher increase of property value is registered in comparison to other energy neutral renovation concepts. These findings provide an important support and inspiration for designers and decision makers operating in the field of deep energy retrofit.