Building retrofit addressing occupancy: An integrated cost and environmental life-cycle analysis

Building retrofit can lead to important savings in operating cost and environmental impacts; however, the actual savings depend on future house occupancy, which is generally not taken into account. The goal of this article is to carry out an integrated (cost, environmental and energy) life-cycle (LC) assessment of alternative roof and exterior-wall insulation retrofit strategies for a single-family house addressing occupancy. Alternative scenarios were defined by type of use (residential and office) and occupancy level (low and high), set-points and family size. LC impacts were calculated for five environmental categories and non-renewable primary energy showing that an insulation level threshold (where total LC impacts are minimized) can be identified for exterior-wall retrofit (60-70 mm for all scenarios) and roof retrofit (90-100 mm for low residential occupancy; 80-90 mm for high residential occupancy and office use). Recommendations can be provided to enhance the retrofit performance of historic buildings in Southern Europe, depending on their use and occupancy level. Highly-insulated retrofit is more beneficial for high occupancy levels with higher thermal comfort conditions. No benefit is derived from incorporating insulation for lower comfort conditions. Interior insulation on exterior walls presents higher savings than exterior insulation.