Life-cycle environmental and cost assessment of building retrofits: Evaluating conventional and streamlined approaches

Building retrofits can promote a significant reduction in the environmental load and operating costs of the European building stock. In Portugal there are two million households needing refurbishment (34% of the Portuguese building stock). Most of those buildings are among the largest contributors to the poor energy performance of the building sector. However, given their long life span, it is essential that designers and developers are encouraged to identify effective strategies that reduce the overall burden of the building in life-cycle (LC) perspective. Life-cycle approaches have been extensively applied to analyze building environmental impacts and costs. However, they are time consuming and resource-intensive to implement, preventing a more widespread use. Additionally, they are usually performed in late design stages when significant reduction in total life-cycle impacts is costly to achieve. The main goal of this PhD thesis is to explore both conventional and streamlined LCA and LCCA approaches to identify the most appropriate strategies to improve the LC environmental and economic sustainability of building retrofits for family households and office buildings in South European climates. An integrated cost and environmental conventional LC approach combined with thermal dynamic simulation was developed and implemented to different building retrofit projects (a single-family house, an apartment, and an office building). Final and primary energy, environmental impacts and costs are assessed and trade-offs identified. LCCA is performed using the equivalent annual cost method to calculate the net annual savings. A sensitivity analysis addressing occupancy is performed to increase the robustness of the results. A novel approach was developed to streamline LCA and LCCA for building retrofits that both accommodates varying amounts (and quality) of information on retrofit design and provides both estimates and uncertainty in the estimate for both environmental and economic performance. A framework was developed that fully integrates a streamlined embodied LCA, statistical-based operational energy and cost models. The method comprises the application of structured under-specification, probabilistic triage, and guided sequential specification. Drawing on the results, some recommendations can be provided to enhance the environmental performance of building retrofits in historic city centers with load-bearing stone wall systems in South European buildings from the late 1800s to the early 1900s, pointing to a roof and exterior-wall insulation thickness threshold (where total life-cycle impacts are minimized) depending on the type of house and occupancy. Highly-insulated retrofit strategies are more beneficial for high occupancy levels with higher thermal comfort conditions. Exterior-wall with 40 mm insulation presents the highest marginal savings and the lowest environmental impacts. There are no benefits in roof insulation of more than 80 mm for all types of occupancy. A sensitivity analysis performed to a set of building cases concluded that highly influential design attributes should be defined early in the design process as it may leverage further design decisions. Occupancy-related parameters have been identified has highly influential to the total LC impacts of buildings retrofit irrespective to location, type of house and wall-system. Three retrofit strategies were assessed to compare the recommendations derived from the streamlined approach with the previous conventional LCA studies. The model identified the same preferred options as conventional LCA with only five to eight building design attributes specified. The streamlined approach allows the designers to either identify an environmentally and economically superior design or evaluate the design choices by increasing specification efficiently until the level of resolution in the result is sufficient to make decisions. An equally important aspect is to enhance the potential of this approach for widespread use of LCA and LCCA as decision-making tools in the current uilding design practice.