Politecnico di Milano, piazza Leonardo da Vinci 32, Milano (Italy) 3 Dipartimento di Elettronica e Informazione (DEI),

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1 Life Cycle Assessment of different refurbishment strategies for an historical building: the importance of the indicators for the comparison of synthetic and natural materials Gianluca Ruggieri 1, Giovanni Dotelli 2, Paco Melià 3 and Sergio Sabbadini 4 1 Università dell Insubria, via Dunant 3, Varese (Italy) 2 Chemistry, Material and Chemical Engineering Department, Politecnico di Milano, piazza Leonardo da Vinci 32, Milano (Italy) 3 Dipartimento di Elettronica e Informazione (DEI), Politecnico di Milano, Via Ponzio 34/5, Milano, Italy 4 Disstudio, Via Piolti de' Bianchi 48, Milano (Italy) gianluca.ruggieri@uninsubria.it; giovanni.dotelli@polimi.it; paco.melia@polimi.it; s.sabbadini@disstudio.it Abstract: The adoption of stricter minimum efficiency standards are decreasing the impact of the operational phase of building. The energy consumption and environmental impact of the construction and of the demolition phases will therefore play a growing role. Only a life cycle perspective can properly evaluate the building economic and environmental performances and support the choices of the designer. In this paper we analyse different intervention strategies for the energy refurbishment of an historical building, the former silk spinning mill located in Valmadrera, not far from Lake Como in northern Italy. The LCA results of the different strategies and the different options are discussed: they are strongly influenced by the indicator chosen for the evaluation (global warming potential, ecological footprint, Eco-indicator 99). The methodological issues that arise from the analysis are therefore underlined in the conclusions. Keywords: Historical buildings, environmental impact indicators, life cycle assessment, natural materials, synthetic materials 1 Introduction The recent recast of the Energy Performance of Building Directive, paves the way for future nearly zero energy buildings. In this perspective the energy consumption and the environmental impact of the operational phase of buildings are set to decrease. At the same time, the energy consumption and environmental impact of the construction and of the demolition phases will play a growing role. A Life Cycle perspective is therefore essential to evaluate the economic, energetic and environmental balance of a building, particularly those undergoing deep renovation. This paper presents different intervention strategies for an historical building: the former silk spinning mill located in Valmadrera, not far from Lake Como in northern Italy, active since Different possible wall insulation strategies are considered: a conservative strategy, with a lower

2 visual impact on the external facade, to preserve the historical value of the building; an ameliorative strategy, that includes thermal insulation on both the internal and external surface of walls; an innovative strategy, that include demolition and reconstruction of some part of those part of the building that were added during the twentieth century. For all the strategies, two different options are compared: one that adopts synthetic materials, the other one natural materials. The LCA results of the different strategies and the different options are discussed: they are strongly influenced by the indicator chosen for the evaluation (global warming potential, ecological footprint, Eco-indicator 99). The methodological issues that arise from the analysis are therefore underlined in the conclusions. 2 Life cycle analysis in the building sector: a fragmented picture Life cycle analysis has been introduced in the building sector since the early 1990 s and has become an important support instrument to designers. LCA of buildings differs in many respects from the analysis of consumer products, for which it was initially developed. A building has generally a longer lifetime, has bigger dimensions, and is made up of several materials having different properties or functions. A building can have different functions, even for short time periods. Therefore each building is a unique product, and building LCA can be hardly standardized. For these reasons, LCA in the building sector is a research field under constant evolution. Most of the published studies focalise on a single material or a single building component, because it is difficult to define borders and methodologies for the analysis of a complete building. A deep literature survey has been published in 2009 (Ortiz et al., 2009) and includes very different kind of studies. The studies may differ in terms of completeness (phases of the life cycle included, evaluation methods), transparency (description of the methodological assumptions) and scientific rigor. But, even most importantly, the researchers may choose different assumption and therefore their results can hardly be compared. For example differences may be highlighted in the choice of the functional unit, of the allocation procedures, in the disposal scenarios, in the electricity mix, in the impact categories and so on (Werner & Richter, 2007). More recently, several efforts have been devoted to the harmonisation of different methodologies for building LCA. For example, the Council of European Producers of Materials for Construction (CEPMC) has established a European technical committee (CEN/TC 350, Sustainability of construction works) that is responsible for the development of voluntary horizontal standardized methods for the assessment of the sustainability aspects of new and existing construction works and for standards for the environmental product declaration of construction products (Baldo et al., 2008). This work is presented in a recent publication (König et al., 2010). 3 Research Methodology The research presented in this paper aims at evaluating different refurbishment strategies for an historical building the former silk spinning mill located in Valmadrera, not far from Lake Como, active since In 1864 more than three hundred people used to work in this architectural complex. The analysis was developed on three buildings: two of them were built in the 1820 s (the silk spinning mill and the house of

3 the watchman) and are protected by the Ministry of Culture because of their special historical merit; the third one was built in the 1960 s and connects the two historical buildings. Figure 1. Cross sectional view of the three buildings: the silk spinning mill (left); the 1960 s extension (centre); the house of the watchman (right). (Source Colombo and Salvoni, 2010) 3.1 Intervention strategies The intervention strategies analysed aim at improving the energy performance of the three buildings through the insulation of walls. This paper doesn t consider substitutions of other parts of the envelope (roof, windows) or of the heating systems that can achieve further performance improvements. For the two historical buildings, two different strategies are proposed: a conservative strategy, with a lower visual impact on the external facade, to preserve the historical value of the building; an ameliorative strategy that includes thermal insulation on both the internal and external surface of walls. For the 1960 s building we present only an innovative strategy that may include demolition and reconstruction of some part of those part of the building that were added during the twentieth century. For all the three strategies, two different options are compared: one that adopts synthetic materials, the other one natural materials. The comparison is developed between two options that obtain the same thermal transmittance. The calculated thermal transmittance of the walls in existing historical buildings is 2 W/m 2 K. The conservative strategy would reduce the transmittance to 0,66 W/m 2 K (a 67% decrease compared to the existing situation) while the ameliorative strategy would obtain a 0,31 W/m 2 K transmittance (85% decrease). The 1960 s building walls have a 3 W/m 2 K transmittance that can be reduced to 0,31 W/m 2 K through the innovative strategy (90% decrease). 3.2 Materials and wall layers design The choice of the materials and the design of the wall layers were carried out having in mind the problems that may arise on the construction site. Therefore all the options identified can be actually adopted in real situations. The design options adopt only materials already included in LCA database or already analysed in literature, plus some earth plasters that were analysed with a specific LCA investigation (Resi and Zannetti, 2010).

4 The conservative-ecological design option consists of an external layer of painting (2 mm), the existing wall and an internal 50 mm layer of insulating earth plaster covered with a finishing earth plaster layer (3 mm) on the inside. The conservativesynthetic design option consists of the same external layer of painting (2 mm) and the existing wall, while on the inside it includes a 90 mm layer of insulating plaster (consisting of a mix of lime, cement and expanded polystyrene, EPS) covered with a levelling and finishing lime layer (4 mm). The ameliorative-ecological design option consists of an external levelling and finishing lime layer (3 mm), followed by a 70 mm layer of lime and cork and a 3 mm levelling lime layer. On the inside it includes an internal 60 mm layer of insulating earth plaster covered with a finishing earth plaster layer (3 mm) on the inside. The ameliorativesynthetic option consists of an external levelling and finishing cement layer (3 mm), followed by a 70 mm of insulating plaster (consisting of a mix of lime cement and expanded polystyrene, EPS) and a 3 mm levelling lime layer. On the inside it consists of a 70 mm EPS board covered with a finishing cement layer (3 mm). The innovative-ecological design option may only be adopted on the 1960 s extension and requires an external covering of fir wood staves, a cavity containing wood laths and finally a cork board (80 mm); on the inside of the reinforced concrete pillars a mineralised wood wool board (15 mm) will be mounted. The board will be plastered with an earth plaster layer (15 mm) and a finishing earth plaster layer (3 mm). The innovative-synthetic design option includes an external fiber cement siding board (8 mm), followed by a cavity containing wood laths and finally a EPS board (100 mm); on the inside of the reinforced concrete pillars a lime plaster layer (30 mm) covered with a finishing lime plaster layer (4 mm). The conservative and the ameliorative strategies are alternative solution. The choice between them will depend by the decision of the authority in charge of the cultural heritage protection (Soprintendenza per i beni Architettonici e per il Paesaggio). If the Soprintendenza wants to preserve the façade, then the designer will be forced to choose the conservative strategy. Otherwise the ameliorative strategy can be adopted. The 1960 s extension is not protected and therefore the innovative strategy will be surely adopted. Therefore, in the following pages, both the conservative and the ameliorative strategies will include the innovative intervention. 3.3 Life Cycle Analysis (LCA) This paper presents the evaluation of environmental impacts of the intervention on all the walls of the buildings considered. Therefore the functional unity adopted in the analysis is the entire surface involved in the opaque envelope retrofit of the three buildings (see Table 1). Table 1. Total vertical opaque surfaces analyzed Building Surface (m 2 ) Historical buildings s extension 151

5 The time horizon of the analysis includes the retrofit intervention and the operational phase of the buildings. The evaluation of the operational phase considers the primary energy demand of the building under the different intervention strategy. Table 2 provides the result of the calculation obtained through the energy certification procedure developed in Lombardia (Cened+). Only energy consumption for heating is considered. Table 2. Annual primary energy demand of the buildings for heating Primary energy demand (kwh/m2 year) Ex ante 279,2 Conservative strategy 210,4 Ameliorative strategy 196,0 The primary energy demand reduction is not satisfactory, and would lead to results well above the current minimum standards in Lombardia, but this analysis doesn t consider substitutions of other parts of the envelope (roof, windows) or of the heating systems that can achieve further performance improvements. The LCA was performed in Simapro, one of the most widely used programs for these analyses. The data were derived from the Ecoinvent database and can be therefore considered as secondary data (derived from literature). Only data regarding the earth plasters were derived from a specific analysis on primary data made available by the producer (Fornace Brioni). 3.4 Environmental impact indicators Environmental impacts were assessed using three different indicators: Global Warming Potential (GWP; Forster et al., 2007), ecological footprint (Wackernagel and Rees, 1996) and Eco-indicator 99 (EI99; Goedkoop and Spriensma, 2001). In LCAs, GWP is measured in kilograms of carbon dioxide equivalent. The ecological footprint measures environmental impacts in terms of land occupation. Originally developed to compare the human appropriation of natural resources with the regenerative capacity of ecosystems on a geographic scale (from the regional to the global one), it is increasingly used also in LCA analyses. In this context, it is measured as the total surface, integrated over time, of land and/or sea consumed (directly or indirectly) to produce biological resources and to absorb carbon dioxide emissions deriving from the combustion of fossil fuels and from the production of cement. EI99 is an aggregator of different impact indicators. Widely utilised as a standard indicator for LCAs, it EI99 disaggregates environmental effects into eleven impact categories, that in turn are grouped under three macro categories (human health, ecosystem quality and resources depletion). Impacts for the different categories are weighted, normalised and finally aggregated in a unique value. 4 Findings and Discussion 4.1 Results of the LCA The impact of the retrofit of the different intervention strategies in terms of GWP is shown in Figure 2. The ecological design options systematically show a lower impact compared to the equivalent synthetic options.

6 Figure 2. GWP impact of the retrofit for the different design options. For the conservative strategy, the GWP of the ecological option is 50% lower than that of the synthetic one. Concerning the operational phase, the energy performance of the two options is equivalent. Therefore, the result of the comparison does not depend on the option chosen (ecological vs. synthetic) but depends only on the strategy (conservative vs. ameliorative). The decrease in primary energy demand causes a decrease in the environmental impact (Table 3). Both strategies achieve a carbon dioxide emission saving of more than 40 t compared to the current situation. Table 3. Annual carbon dioxide emission under different intervention strategies Greenhouse gases emissions (t CO 2,eq /year) Ex ante Conservative strategy Ameliorative strategy Since the retrofit causes positive impacts (i.e. environmental costs), while the operational phase causes negative impacts (i.e. environmental benefits) thanks to the insulation, it is interesting to investigate the payback time, namely the time needed to compensate the emission caused by the retrofit through the decrease in the emissions in the operational phase. Table 4 shows the payback times associated with different intervention strategies. In all the four scenarios considered the payback time is shorter than one year.

7 Table 4. Carbon dioxide emission payback time of the different retrofit options Retrofit option Emissions caused by retrofit (t CO 2,eq ) Avoided emissions (t CO 2,eq /year) Payback time (months) Conservative-ecological Conservative-synthetic Ameliorative-ecological Ameliorative-synthetic The synthetic options have a lower impact in terms of ecological footprint compared with the equivalent ecological options (Figure 3). During the operational phase both options guarantee a lower footprint, thanks to the improved energy performance of the building (Table 5). The payback times of the impact are rather short (between 11 and 20 months, Table 6). In less than two years, a favourable environmental balance is achieved also in terms of ecological footprint. Table 5. Ecological footprint under different intervention strategies Ecological footprint (hectares) Ex ante 47.7 Conservative strategy 35.9 Ameliorative strategy 33.5 Figure 3. Ecological footprint caused by the retrofit for the different design options.

8 Table 6. Ecological footprint payback time of the different retrofit options Retrofit option Ecological footprint of the retrofit (ha x years) Avoided footprint (ha) Payback time (months) Conservative-ecological Conservative-synthetic Ameliorative-ecological Ameliorative-synthetic The comparison of the different retrofit options through EI99 shows lower impacts for the synthetic options compared to the correspondent ecological options, as shown by the impact score (Figure 4). Considering the operational phase, all the retrofit options guarantee a decrease of the impacts in all damage categories compared to the ex-ante situation (Table 7). Figure 4. Impacts caused by the retrofit as calculated through EI99 Table 7. Impacts of the operational phase as calculated through EI99 Human health damage Ecosystems damage Resource damage Total damage Ex ante Conservative strategy Ameliorative strategy Discussion The results of our analysis are deeply influenced by the indicator chosen. The more intuitive results are those expressed in terms of GWP: the use of natural materials, like those envisaged in the ecological options, guarantees lower impacts thanks to the absorption of carbon dioxide by trees and crops through photosynthesis and the following storage as carbon in the biomass. Considering the intervention on the 1960 s building, the use of vegetal materials determines a negative net balance of greenhouse

9 gases emissions, i.e. the absorption exceeds the emissions. Therefore, irrespective of the strategy (conservative or ameliorative) chosen for the historical building, ecological options are always preferable to synthetic ones with regards to the reduction of greenhouse gases emissions. In contrast, the comparison in terms of ecological footprints favours the use of synthetic materials: a result that may be surprising at a first glance. Analysing the distribution of the impacts in the different land use categories (Figure 3), is possible to verify that for the synthetic options the impact due to carbon dioxide emissions is the most important one, while for ecological options direct land occupation has the predominant role. The production of natural materials (such as wood or straw) is actually more landdemanding than the production of synthetic materials, a fact that should be taken into account. However, it is worth noting that, even if the impact caused by the production of natural materials may be higher in terms of quantity, it may be preferable in terms of quality. In fact, a land occupied by industrial activities is subject to a strong disturbance, while the same land can retain most of its ecosystem functions if used for agricultural purposes. It is important to underline that one of the major shortcomings of the ecological footprint is the fact that it accounts only for impacts on the carbon cycle, while it does not account for the impact of pollution on other important biogeochemical cycles, such as those of nitrogen, phosphorus or sulphur. The impact assessment based on EI99 is also favourable to the synthetic options. For both options (ecological and synthetic) the most important damage categories are the consumption of fossil fuels and the respiratory effects due to pollutant emissions. For the synthetic options a third important source of damage is linked to greenhouse gases emissions, while for the ecological options land use is an important damage category. The gap between the different options is lower than the one calculated with the ecological footprint, because land occupation is only one of the several impact categories included in the global indicator. 5 Conclusion and Further Research The results presented confirm the importance of an approach based on different impact indicators, providing different, and complementary, viewpoints to the assessment of the overall environmental impact of various building design alternatives. On the other hand, however, our analysis highlights the need to develop indicators that are able to capture not only the quantitative differences between the impacts of different options, but also the qualitative ones. If LCA is used to support public decisions, the indicator chosen should reflect the objective(s) of the decision-makers. For example, if the main goal is the decarbonisation of the economy, the GWP is the best indicator, while if the goal is a generalized reduction of environmental impacts, Eco-indicator 99 may be a better choice. A major shortcoming of the ecological footprint is that it takes into account only the quantity of land appropriated by a human activity, without considering the effects of this appropriation on land quality. In particular, the ecological footprint may be useful to compare options requiring a similar land use (e.g. to choose among different

10 synthetic retrofit options), while it is not adequate to compare options implying very different land use ways (e.g. to choose between synthetic vs. natural retrofit options). In this respect, an ecological footprint analysis incorporating land disturbance would add crucial information to policy for long-term planning (Lenzen et al., 2007). Further research is envisaged in order to include all natural materials in LCA databases. In this way, further comparisons may be developed among different retrofit options all utilising natural materials. 6 Acknowledgements The results presented in this paper are based on the analyses of two Master theses conducted at the Politecnico di Milano (Colombo and Salvoni, 2010, Resi and Zannetti, 2010). Data for the LCA of earth plasters were provided by the producer Fornace Brioni. 7 References Baldo, G.L., Marino M., Rossi S. (2008) Analisi del ciclo di vita LCA. Edizioni Ambiente, Milano Colombo, E. and Salvoni, M. (2010) Architettura sostenibile e patrimonio archeologico industriale: il recupero del Filandone Gavazzi di Valmadrera (Lc). Master thesis in Environmental Architecture, Politecnico di Milano, Milan, Italy (in Italian). Forster, P. et al. (2007) Changes in Atmospheric Constituents and in Radiative Forcing. In: Solomon, S. et al., Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, UK and New York, NY, USA, pp Goedkoop, M. and Spriensma, R. (2001) The eco-indicator 99. A damage oriented method for Life Cycle Impact Assessment. Methodology report. Pré Consultants, viewed 13/10/2011. König, H., Kohler, N., Kreißig, J. Lützkendorf, T., (2010) A life cycle approach to buildings Principles, Calculations, Design Tools. Detail Green Books, Munich. Lenzen, M., Borgström Hansson, C. and Bond, S. (2007) On the bioproductivity and land-disturbance metrics of the Ecological Footprint. Ecological Economics, 61, pp Ortiz O., Castells F., Sonnemann G. (2009) Sustainability in the construction industry: A review of recent developments based on LCA, Construction and Building Materials; 23, pp Resi, S. and Zannetti, A. (2010) Efficienza energetica e sostenibilità in edilizia. Scelta e caratterizzazione dei materiali per la riqualificazione di un edificio storico tramite LCA. Master thesis in Environmental Engineering, Politecnico di Milano, Milan, Italy (in Italian). Wackernagel, M. and Rees, W. (1996) Our ecological footprint: reducing human impact on the Earth. New Society Publishers, Gabriola Island, BC. Werner F., Richter K. (2007) Wooden Building Products in Comparative LCA, International Journal of Life Cycle Assessment; 12 (7), pp