Studio LCA degli interventi per il miglioramento delle prestazioni ambientali ed energetiche nella ristrutturazione edilizia di una cascina lombarda

Nowadays, there is a general consensus about the fact that the environmental impacts generated by the building sector are quite severe; nonetheless, this is a human activity which is considered indispensable for the future development; the house is perceived by most persons as a primary need and certainly a positive social and economic indicator. For sure, the sector is a major consumer of intermediate products and related services; moreover, the poor energy performance of buildings and the large use of non-renewable resources in the production and transport of construction materials may have a very detrimental effect on the environmental sustainability. Therefore, a careful choice of construction materials can very much help reduce global environmental impacts; so, a larger use of building materials of natural origin (e.g. wood, hemp, kenaf, cork, clay and lime) could be very beneficial to save non-renewable resources. In addition, most natural materials have thermal and hygrometric performances comparable to those of their synthetic counterparts. So, good thermal building insulation as well as high indoor air quality and comfort could be also guaranteed by adopting new paradigms in constructions. However, being natural is not sufficient to guarantee that a material or a product is more environmentally sustainable than a synthetic one, and in fact it is not always so. Luckily, there are objective and quantitative methodologies that can be safely used to assess environmental sustainability; one of these is the Life Cycle Assessment. The main goal of this thesis has been to assess the environmental sustainability of the building retrofitting by using natural materials with respect to the more conventional option of using synthetic ones. To this purpose, the case study of an old dwelling, typical of the Lombardia countryside, la Corte di Casatenovo, has been investigated. The retrofitting has been realized just during the thesis period, so there has been the great opportunity of collecting primary data and monitoring the construction work in real time. Special care has been devoted to a class of natural materials whose popularity seems increasing; hemp-derived building materials, in particular hempcrete and hemp fiber mats, have been studied in greater detail in the recent literature. Indeed, hemp is a crop that in recent years is finding wide acceptance in building industry due to the fact that it requires no fertilizer or large amounts of water, has low energy consumption during cultivation, grows very quickly and has countless applications in the realization of buildings materials such as hemp-lime or hemp panels. In order to compare the environmental performances of natural materials two different scenarios in the building retrofitting have been considered: ecological scenario, that involves the use mostly of natural materials (real case study), and synthetic scenario, which refers to a traditional building renovation made with materials of common use in the practice. The comparison between the two scenarios was done maintaining the same thermal performance which means the same thermal transmittance. A secondary purpose was to compare, only for the ecological scenario, impacts of renovation and use phase. The study follows assessment procedures and guidelines of international (ISO 14040) and UK (PAS 2050) standards. The renovation takes into account three main phases: production phase of construction materials, which involves the realization of a final product (e.g. panel and flooring), construction phase, which includes laying and installation of the products to form the structures (floors and walls) and finally the use phase of dwelling (only for ecological scenario) assessed on the average life time of a building supposed equal to 80 years. Disposal and end of life of the building are discarded. The functional unit defined for the building renovation is 1m2 of usable surface. Primary data were collected for processes and materials that have no existing information. Life cycle assessment was carried out using the SimaPro 7.3 software. Considering the boundaries and assumptions made, the results demonstrate that the functional unit, in the ecological scenario, could sequestrate 76.8 kg of carbon dioxide with net greenhouse gas emissions of 34.9 kg CO2 eq; instead, in the synthetic scenario, sequestration of carbon dioxide was about 18 kg with net emission of 171.4 kg CO2 eq (results obtained with Greenhous Gas Protocol). Moreover, further results were obtained by adopting different category indicators such as Cumulative Energy Demand (CED), ILCD 2011 Midpoint and Recipe Endpoint. The use of different impact indicators strengthened the idea that the use of construction materials of natural origin may effectively help reduce the environmental burden of the building sector. Last but not least, the work has confirmed that in normal building the operation phase is largely overwhelming the construction one.