Life cycle assessment of prefabricated buildings towards a building stock approach

Buildings are big consumers of energy and materials, and significant producers of waste and emissions. Buildings are increasingly more energy efficient, but the rising number of buildings balances the impact reduction of single buildings; therefore, building stock life cycle impacts are a growing problem. Moreover, energy efficiency is sometimes achieved through increased embodied impacts, offsetting the impact reduction during the use phase. To achieve global and European Union (EU-27) targets, the impacts of buildings should be reduced towards a more sustainable construction sector while increasing the competitiveness of the construction sector. Prefabricated buildings may be a way to accomplish the construction sector's dual challenge: reducing buildings' impacts and costs. This thesis has two main goals: First, to assess life cycle environmental impacts and costs of prefabricated buildings and compare them with conventional buildings. A life cycle assessment (LCA) model was developed to assess prefabricated and conventional single-family houses, mapping the main differences between both construction approaches and disclosing tradeoffs, e. g. , between construction and use phases. The LCA focused on two single-family houses built in Portugal and alternatives including different house sizes, structural materials, final house locations, and insulation levels. A “cradle-to-site” assessment of a prefabricated house was performed focusing on embodied impacts; a “cradle-to-use” LCA balanced embodied and operational impacts to disclose tradeoffs between both phases; and a “cradle-to-grave” LCA assessed the environmental impacts, costs, waste, and production time of different prefabricated and conventional buildings using different structural materials. Second, a building stock approach was developed and implemented to assess the influence of prefabrication wide adoption on EU-27 building stock. This goal also aims to contribute methodologically to the assessment of the introduction of disruptive technology– in this case, prefabrication – in a large set of products in use – the building stock. The building stock model (BSM) developed included the definition of archetypes representing EU-27 building stock, modular life cycle inventory (LCI) to calculate impacts, building information modeling (BIM) to forecast energy needs and extracted quantities, and statistics to estimate results at a country and EU-27 building stock levels. BIM integration allows the streamlined LCI and energy simulation. The proposed modular LCI calculates impacts of a large set of buildings using proxies such as building elements area, number of components, workdays, distance to the site. The developed building stock approach creates a large dataset of results combining alternatives: e. g. , construction approaches, typologies, structural materials, insulation levels, and final location; while addressing regional variability with different climates, costs, electricity mixes. The results from the life cycle model developed show that compared with conventional, during construction prefabricated single-family houses can use one-fourth of materials, produce the same fraction of waste, reduce 20% of costs, and take one-third of the time to be built. During the use stage, prefabricated buildings have similar energy performance (or better if insulation is adjusted to local climate) and produce one-fourth of the waste. At the end of life, prefabricated buildings produce one-fourth of the waste, being this waste 40% more recyclable, thus balancing up to 20% of the embodied impacts.