Deep energy retrofits using different retrofit materials under different scenarios: Life cycle cost and primary energy implications

Deep energy retrofits of existing buildings can contribute to achieving a renewable-based society, though they are mostly lacking in the EU. To understand the cost and primary energy savings of deep energy retrofits, all life cycle phases, including construction, operation, maintenance and end-of-life, must be considered. The initial building without retrofit must be analysed over its remaining lifetime covering energy operation, maintenance and end-of-life implications that change with a retrofit. Such a method is applied to a multifamily building retrofitted to two passive house standards limiting annual final heat use to 50 and 30 kWh/m2. Energy improvements to the building envelope are analysed considering different versions of initial cladding materials and retrofit materials, and different economic and electricity supply scenarios. A retrofit to 50 kWh/m2 is profitable for all economic scenarios while the 30 kWh/m2 version is profitable for most of the scenarios giving net primary energy savings of 57–60% and 63–72%, respectively, compared to the non-retrofitted building. The cost of different retrofit materials is similar, while the primary energy use is much lower for wood-based materials. The changed costs and primary energy use for the non-retrofit building, in maintenance and end-of-life phases, varies depending on assumed initial cladding materials.