Simplification in life cycle assessment of single-family houses: a review recent developments

1 SIMPLIFICATION IN LIFE CYCLE ASSESSMENT OF SINGLE-FAMILY HOUSES: A REVIEW OF RECENT DEVELOPMENTS Bernardette Soust-Verdaguer1, Carmen Llatas2, Antonio García-Martínez3 1Department of Building Construction I, Escuela Técnica Superior de Arquitectura, University of Seville, Reina Mercedes 2, 41012 Seville, Spain; email: [email protected] 2Department of Building Construction I, Escuela Técnica Superior de Arquitectura, University of Seville, Reina Mercedes 2, 41012 Seville, Spain; email: [email protected] 3Department of Building Construction I, Escuela Técnica Superior de Arquitectura, University of Seville, Reina Mercedes 2, 41012 Seville, Spain; email: [email protected] Corresponding author: Bernardette Soust-Verdaguer Mailing Address: Department of Building Construction I, Escuela Técnica Superior de Arquitectura, University of Seville, Reina Mercedes 2, 41012 Seville, Spain. Phone: (+34) 95 455 65 91 Email: bso[email protected] 2 SIMPLIFICATION IN LIFE CYCLE ASSESSMENT OF SINGLE-FAMILY HOUSES: A REVIEW OF RECENT DEVELOPMENTS ABSTRACT Life Cycle Assessment (LCA) is globally recognized as one of the most complete methods for environmental assessment of buildings. Literature assumes that its applications in the building sector are prejudiced regarding complexity and difficulty. However, simplification is necessary, since it can facilitate LCA application in buildings. Moreover, growing interest on reducing environmental impact in the building sector, as well as the relevance of single-family houses on CO2 emissions have become key points on the wide spread of LCA. Therefore, this paper presents a research study about simplification in LCA recent studies applied to singlefamily houses. The review focuses on 20 cases that were analyzed according to ISO 14040, ISO 14044, EN 15978, and EN 15804 standards. The main objective was to identify the simplification strategies assumed in each paper, to clarify and to help to promote further developments on LCA. This paper examines system boundary definition, data sources, life cycle phases included, and environmental impact indicator calculated in case studies. Results show the variety of simplifications identified. They affect physical model definition, life cycle scenario definition and communication of results. In most cases, the functional unit was the complete building, the life cycle scenario definition included production, use and demolition phases, and the most considered environmental impact indicator was GWP. Finally, new challenges and recommendations were defined in order to establish common criteria to develop simplification strategies that allow results comparability in LCA of single-family houses. Keywords: Life Cycle Assessment; simplified LCA; environmental assessment methods; environmental assessment impacts; review. Abbreviations: AP, Acidification Potential; BIM, Building Information Modelling; CC, Climate Change; CED, Cumulative Energy Demand; EPD, Environmental Product Declaration; ET, Ecological Toxicity; GHG, Green House Gases; GW, Global Warming; HTP, Human Toxicity Potential; LCA, Life Cycle Assessment; LCI, Life Cycle Inventory; LCIA, Life Cycle Impact Assessment; MRR, Maintenance, Repair and Replacement; PMF, Particulate Matter Formation; WD, Water Depletion. 3 1. INTRODUCTION Current environmental problems have led to the development of measures for reducing the impact of human activities in the environment. These measures aim to control CO2 emissions, improve efficiency and save resource consumption. The last COP21 -also known as 2015 Paris Climate Conferencereinforced global compromises to reduce Global Warming and concluded by the signature of an agreement for reducing Carbon Emissions [1]. The building sector represents 19% of all global 2010 GHG emissions [2]; as well it is also a major consumer of natural sources [3]. Moreover, single-family houses have an important role in reducing environmental impacts of the building sector, since for example 60% of the EU CO2 emissions of residential sector come from single-family houses [4]. LCA is recognized as a useful method to assess environmental impact in the building sector. Wiessenberger et al. [5] demonstrated the growing interest in LCA of building by the increasing number of publications of scientific studies in the last 20 years. Cabeza et al. [6] review, also demonstrated the use of LCA in the building sector through the organization of a large number of literature that includes construction products, systems, buildings, and civil engineering constructions. Lotteau et al. [7] developed a critical review of LCA applications at neighborhood level. The review exposes the trend towards the application of LCA on an urban scale, although literature about the subject is still scarce. The study demonstrates the heterogeneity of methodological choices and also develops recommendations to promote future research. Buyle et al. [8] review focused on building applications of LCA and evidenced that LCA involves making a model that simplifies reality. Various LCA studies recognize that complexity and uncertainties are barriers for the widespread use of LCA of the built environment [9,10]). Moreover, “typical” applications of LCA in buildings are admitted as time-consuming and complex processes[11]. In the European Context several projects have been developed aiming to adapt LCA methods to the building sector. Moreover, the standardization work on LCA of buildings -CEN TC 350- defines EN 15804 [12] and EN 15978 [13] standards; and provides a methodological framework of the information to be included, stages and communication of results [14]. However, the advances identified on LCA of buildings, studies about simplification strategies focusing on single-family houses are still scarce. It is assumed that application of the LCA method necessarily involves the simplification of reality; the challenge is the definition of a model so that simplifications do not considerably modify the final results [15]. Several studies [9–11,16–19] recognize the need of reliable simplifications in the application of LCA methods in 4 buildings; especially to extend the scope to early stages of design, reduce effort in data acquisition, enable comparability of results, and allow results to be interpreted independently from the degree of specialization of the technicians. The key aspect is to know how simplifications can modify the representativeness of the results. Therefore, this paper analyses recent developments in the application of LCA in single-family houses, focusing on methodological aspects and simplification strategies according to ISO 14040 [20], ISO 14044 [21], and EN 15978 [13] LCA standards. The main objective was to identify the simplifications and modelling assumed on each study, to clarify and to help promote further developments on LCA. Twenty selected cases are included in the following review. Some of them are complete building LCA application and others are focused on representatives systems, elements or parts of the building. 2. LCA APPLIED TO BUILDINGS 2.1. Barriers on LCA applied to buildings The LCA method is based on the quantification of environmental impacts of a product throughout its life cycle, from "cradle to grave" [20,21]. In general terms, ISO 14040 standards establish the stages for LCA application. LCA approach adapted to building is defined in EN 15978 [13] that represents a methodological guide for the quantification of environmental impacts on buildings. Fig. 1. Scheme of the information modules for the different stages of evaluation of the building based on 15978 [13]. 5 EN 15978 [13] is organized according to the “modules principle” of building life cycle, including the four stages of life cycle –product, construction, use, end of life- ([13,19]. These stages and modules are shown in Figure 1 and cover from A1 to C4 "impacts and environmental aspects" developed within the system boundary, while D modules cover benefits and loads that go beyond the system boundary. The standards also provide the guidelines for functional unit, system boundary and scenario definitions. The functional unit is a “quantified performance of a product system for use as a reference unit" [21], and it includes the physical and functional characteristics of the building. System boundary limits the processes included in the assessment. The scenarios are hypothesis applied to the subject of study that relates physical characteristics with time variable [13]. EN 15978 [13] also defines the structure of results communications and a list of environmental indicators that have to be considered as shown in Table 1. Results have to be expressed according to the list of indicators included in Table 1, separated by stage (production, construction, use, end of life, recycle) and by modules (A1-D) [13]. Table 1. List of indicators described in EN 15978 [13] standard. Environmental impact Resource Use Waste categories and the output flow leaving the system Global warming potential (GWP) Depletion potential of the stratospheric ozone layer (ODP) Acidification potential of land and water (AP) Eutrophication potential (EP) Formation potential of tropospheric ozone photochemical oxidants (POCP) Abiotic resource depletion potential for elements (ADPE) Abiotic resource depletion potential for fossil fuel (ADPF) Use of renewable primary energy excluding energy resource used as raw material (PERE) Use of renewable primary energy resources used as raw material (PERM) Use of non-renewable primary energy excluding energy resource used as raw material (PENRE) Use of non-renewable primary energy resources used as raw material (PENRM) Use of secondary material (SM) Use of renewable secondary fuels (RSF) Use of non-renewable secondary fuels (NRSF) Net use of fresh water (FW) Hazardous waste disposed (HWD) Non-hazardous waste disposed (NHWD) Radioactive waste disposed (RWD) Components for re-use (CRU) Materials for recycling (MFR) Materials for energy recovery (not being waste incineration) (MER) Exported energy (EE) 6 EN 15804 [12] provides calculation rules for Environmental Product Declarations (EPD) and it also includes a methodological framework of Modules A1-A3 of EN 15978 standard [13]. Otherwise, the EPD of building products can be used as product stage modules in EN 15978 [13]. Passer et al. [22] shown the growing interest in EPD of building products, evidenced by the high number of EPD programs that guide CEN/TC 350 standards “Sustainability of construction works”. In the European context the application of LCA method in building sector is promoted by several projects as: REGENER [23], Annex 31 IEA [24], PRESCO [25], IMPRO-Building [26], ENSLIC Building [27], LoRe- LCA [28] and EeB Guide Project [14]. The EeB Guide Project [14] defines three types of LCA in buildings: Screening, Simplified and Complete. The classification is developed according to system boundary definition, the experience of the practitioner, data availability and the state of development of the product or building being assessed [14]. EeB Guide Project [14] also establishes a life cycle stages definition for each LCA study types. For Complete LCA study, all stages and modules defined in EN 15978 [13] are compulsory. In Screening and Simplified LCA types, several stages and modules are optional; depending on the relevance and data availability. For Screening LCA only the following modules are compulsory: Product stages for the building envelope, structure and foundation (A1-3), Operational use of energy (B6) and water (B7). For Simplified LCA type, in addition to compulsory modules considered in Screening type (A1, A2, A3, B6 and B7), the use and end of life stages are also partially included; modules as Replacement (B4), Waste treatment (C3) Disposal (C4) and Benefits (D) are even considered compulsory [14]. Despite the fact that LCA is the most complete tool for the environmental assessment of buildings, their application in buildings is not yet widespread. Some of the main difficulties are the extensive and exhaustive amount of information required, as well as the required experience of the practitioner for calculating impacts [17]. Moreover, architects and technicians involved in the early stages of the design have prejudices about the complexity, precision and arbitrary results [17]. Another difficulty in LCA application is the existence of different methods for impact calculation, so depending on the method different results for identical cases [8] can be obtained. Each method has differences in weighting impact categories; this can lead to different measures for reducing environmental burdens [8]. 7 2.2. Simplifications in LCA In the Spanish context, 150041-1998EX UNE [29] establishes general criteria to simplify the LCA method. The regulation establishes the simplifications that can be carried out in the life cycle inventory phase and the life cycle impact assessment phase. It means that the life cycle inventory analysis can be reduced to the main elements and processes, and the impact assessment phase can be simplified to a few impact categories – mandatory and optional- [29]. Zabalza et al. [17] assessed a residential building in Spain by developing a simplified LCA method. The study focuses on the calculation of operational energy consumption and CO2 emissions. Relevant research papers about LCA of residential buildings and building materials have also simplified the application of LCA. Malmqvist et al. [9] recommend for simplifying the LCA method of buildings: (1) reducing the data acquisition phase –e.g. focusing on larger building elements-, (2) simplifying inventory analysis –e.g. focusing on the most important substances that contribute to a certain impact category-; (3) simplifying the calculation by focusing on a few impact categories and finally, (4) reducing the time of data applications by using CAD applications. Time-reduction of data acquisition strategies are developed in Basbagill et al. [11]. In this study, the uses of Building Information Modelling (BIM) applications to quantify building materials were developed to assess a residential building in USA. The study proposes a method that integrates BIM, LCA, energy simulation, Maintenance, Repair and Replacement (MRR) schedule, and sensitivity analysis software. The method can quickly integrate LCA in the early stages of design. Moreover, Karami et al. [30] simplified data acquisition in the production phase by using EPDs of different building envelopes. The study compares the environmental impact of building envelopes of three residential buildings located in Sweden. They also reduce LCA stages by including only production of envelope materials and energy consumption of the building in operational phase. Modules A4-A5, B1-B5 B7, C and D are included in the study. Kellenberger and Althaus [16] aimed to define the relevance of materials and processes on occasions not considered in simplified LCA of building components. Results demonstrate the incidence of transport and ancillary materials in the impact indicators, and also evidence the irrelevance of building processes and waste cutting. 8 On the other hand, Takano et al. [19] studied the application of the standards EN 15978 [13] and EN 15804 [12] to a referenced wooden building. The authors demonstrate that the standards provide a framework for building assessments, though several difficulties are identified. Data complexity and uncertainties in data collection are underlined. Simplifications in construction phase assessments are suggested, as well as changes in the communication of results. They propose a communication system based on a common method that stimulates environmental consciousness in society. Therefore, despite literature assumes the need to introduce simplifications in the LCA method; few studies have studied the incidence of simplification strategies in the most significant typology in terms of CO2 emissions. 3. MATERIALS AND METHODS The method consisted of two stages: 1) selection of case studies that refer to literature search and the criteria of the cases studies selected, 2) analysis of the LCA applied to single-family houses that includes the LCA phases analysis and the life cycle stages. 3.1. Criteria for selection of case studies Over the last five years, after the publication of EN 15978 [13] and 15804 [12] standards, several studies have been published about LCA of buildings. This paper carried out a selection of recent publications on LCA in single-family houses; typology responsible for the majority of CO2 emissions of building sector. The criteria selected were: 1) publications covered by Scopus and included in the Journal Citation Report, 2) studies based on LCA applied to single-family houses, and 3) studies conducted in the last five years. Selected papers were applications of the LCA method, in which simplifications were identified and analyzed according to LCA buildings standards. 3.2. Criteria for analysis of the LCA applied to single-family houses The analysis was organized in two parts, the first one referred to LCA key phases and the second one was based on life cycle stages definition. The criteria to organize case study was centered on the classification into European and Non-European cases, the scope of the LCA application–partial or complete-, and the characteristics of the house –typical or energy efficient certificated-. 9 3.2.1. Criteria for analysis of LCA phases References to simplification strategies for LCA focus attention on methodological aspects. Therefore, the analysis of simplification strategies in the case studies was centered on functional units, data sources and environmental impact indicators. The goal and scope definition analysis -included in Table 2- was analyzed according to the following aspects: 1) the reference standard to develop LCA; 2) the object of study and a brief characteristic of it –typical or energy efficient certificated-; 3) the functional unit definition –partial and complete LCA applications-, 4) the service life time considered. Table 3 was centered on the data sources and information structure. It analyzes data sources to obtain the main information modules: 1) product –including raw material, transport and manufacturing-; 2) construction, 3) use –including use, maintenance, replacement, repair, refurbishment-, 4) end of life –including demolition, waste processing and disposal-, 5) recycle, 6) transport to construction site, 7) transport to landfill site, 8) energy consumption and 9) water consumption. Table 4 consisted on the analysis of the results including: 1) calculation tools; 2) impact calculation method; 3) environmental impact indicators. 3.2.2. Criteria for analysis the life cycle stage From the literature review, it was detected that LCA of buildings can be focus on certain life cycle stages. Several cases [17,30], for example, were focused on product stages as a strategy to reduce the amount of data and complexity on LCA application. Based on that fact, LCA stages definition became a relevant aspect on LCA of single-family houses. In order to analyze this aspect, a grid was organized to identify stages and modules described in EN15978 [13] -European reference in LCA of buildings. Nevertheless, several non-European cases [31–34] were included. Table 5 resumes the information modules covered by the LCA application. It was focused on identifying the stages that have been selected, as well as the most relevant in case studies. 4. RESULTS 4.1 Selected case studies An overview of recent developments of LCA applied to single-family houses is shown in Table 2, 3, 4 and 5. It includes 14 European cases, 5 Non- European cases and a case that compares both situations. 4.2. Analysis of LCA phases 4.2.1. Goal and scope definition phase The definition of the functional unit had a key role in LCA of single-family houses. According to Cabeza et al. [6], LCA of buildings can be classified into product application (EDP) and building application. The papers 16 Table 3. (continued) Building model Building process Operational consumption Reference Material and products quantification Product stage (A1,A2,A3) Construction stage (A5) Use stage (B1, B2, B3, B4, B5) End of Life stage (C1,C3,C4) Recycle stage (D) Transport to construction site (A4) Trasnsport to lanfill site (C2) Energy Consumption Calculation (B6) Water Consumption (B7) 1. European cases (cont.) Rosselló-Batle et al., 2015 - BEDEC - - - - - - LIDER + CALENER - Rossi et al., 2012 - Bees WORLDSTEEL, CRTI - - - - - - Pleaides + Comfie - Lewandowska et al., 2013 - Ecoinvent v2.2. - Authors estimations - - Vehicle route planning software Vehicle route planning software and other sources. Based on architectural projects and energy certificates Authors estimations based on Minister of Construction [95] Fouquet et al., 2015 - Ecoinvent v3.01 - - - - Authors estimations based on previous research [18] Authors estimations Comfie - Peuportier et al. , 2013 - Ecoinvent. v1.1 and further versions. - - Authors estimations Authors estimations Authors estimations Authors estimations Comfie - 2. Non- European cases Babaizadeh et al., 2015 BEES model Ecoinvent 3.0 BEES model - - Authors estimations Authors estimations Ecoinvent 3.0 BUWAL 250 - EnergyPlus 7.2 - Utama et al., 2012 - Previous research [96] Authors estimations Authors estimations - - - - Authors estimations - Hanandeh, 2015 - ELCD database 2.0 and previous research [97,98] - - Authors estimations Authors estimations Statistic estimations - Statistic estimations and previous research [99] - Islam et al., 2014 BBQ (Builder’s bill of quantity) AusLCI database Ecoinvent - Authors estimations - - Authors estimations Authors estimations AccuRate software - Oyarzo & Peuportier, 2014 - Ecoinvent v1.1 - - - - Authors estimations Authors estimations Comfie and multizone approach Authors estimations based 3. European and Non-European cases Mosteiro-Romero et al., 2014 - Ecoinvent v2.2 - - Authors estimations Authors estimations Authors estimations and previous research [100] Authors estimations REM/DesignTM Software - 17 4.2.3. Life cycle Impact Calculation (LCAI) and interpretation Phases Among the selected papers a wide variety of environmental impact indicators were identified. Different criteria in environmental impact indicators definitions were recognized. Some of them corresponded to global environmental priorities and some of them responded to regional environmental priorities. About Global priorities Table 1 shows EN 15978 [13] environmental indicators categories including: Environmental impact indicators, Resource Use and Waste categories and the output flow leaving the system. 75% of the selected papers analyzed focused on some of those Environmental Impact Indicators, GWP was mostly considered. Strictly speaking, Resource Use indicators and Waste categories indicators were not considered. About local priorities Hanandeh [32] defines the environmental impact indicators by focusing on the most significant environmental problems in Jordan: WD, CC, AP, HTP, and PMF. Islam et al. [44] define global -GHG and CED- and regional categories -water use and solid waste-. On the other hand, several cases focus on CO2 emissions; one of the most significant environmental indicators in climate change mitigation. Moncaster & Symon [101] recommend its calculation as a part of building design process. Rossi et al. [38], Iddon et al. [39], Houlihan et al. [43] calculated Carbon emissions – Embodied and Operational-. Moreover, Rosselló-Batle et al. [60] focused on Embodied and Operational Energy. 18 1 Table 4 Selected cases organized by environmental impact indicators. Reference Impact Calculation method Indicators 1. European cases Houlihan et al., 2014 NA ED, EC, OCE Gervasio et al., 2014 NA ADP –E, ADP –F, AP, EP, GWP, OLDP, POPC Dahlstrøm et al., 2012 ReCiPe v1.03 CC, ED, GHG, PMF, TA Motuzienè et al., 2016 AHP GWP, OLDP, PED Proietti et al., 2013 EPD 2007 and Eco-indicator 99 AP, EP, GER, GWP, NRE, POCP Takano et al., 2015 Previous research [102] NRPEC, RPEC Cuéllar-Franca & Azapagic, 2012 CML 2001 method AP, ADP, EP, FAETP, GWP, HTP, MAETP, OLDP, POCP, TETP Iddon et al., 2013 NA ED, EC, OCE Monteiro & Freire, 2014 CED, CML 2001, Eco-indicator’99 ADP, AP, Car, CC, EP, ET, FAETP, FFD, GWP, HTP, LO, M, MAETP, NRCED, NRE, OLDP, POCP, R, Ra, RI, RO, TETP Rosselló-Batle et al., 2015 - ED, EE Rossi et al., 2013 - EE, OE Lewandowska et al., 2013 Impact 2002+ method Eco-indicator results (weighted impact category indicator results for: AP, EP, GWP, HHC, HHNC, LO, ME, IR, OLDP, RI, TE, TETP) Fouquet et al., 2015 - GWP Peuportier et al., 2013 - AP, B, EP, HH, GWP, O, PED , R, RW, S, W, WC 2. Non-European cases Babaizadeh et al., 2015 BEES 4.0 model AP, CAP, EP, ET, FFD, GWP, HA, HHC, HHNC, OD S, WI Utama et al., 2012 CML 2 baseline 2000 ADP, AP, EP, GWP , HTP, POCP Hanandeh, 2015 ReCiPe Midpoint (H) and Previous research [103] AP, CC, HTP, PMF, WD Islam et al., 2014 Australian Impact and CED CED, GHG, SW, WC Oyarzo & Peuportier, 2014 CML and DALY indicator ADP, AP, CED, EP, GWP, HH, NRW, O, POCP, RW, TETP, W, WC 3. European and Non- European cases Mosteiro-Romero et al., 2014 IMPACT 2002+ AAP, AEP, GWP, NRE, OLDP, TA AAP Aquatic Acidification Potential; AEP, Aquatic Eutrophication Potential; ADP Abiotic Depletion Potential; ADP –E Abiotic Depletion Potential for non-fossil resources; ADP –F Abiotic Depletion Potential for fossil resources; AP Acidification Potential; B Biodiversity; CAP Criteria Air Pollutants; Car Carcinogens; CC Climate Change; CED Cumulative Energy Demand; EC Embodied Carbon Emissions; ED Energy Demand; EE Embo died Energy; EP Eutrophication Potential; ET Ecological Toxicity; FAETP Freshwater Aquatic Eco-Toxicity Potential; FFD Fossil Fuel Depletion; GER Gross Energy Requirement; GHG Green House Gases; GWP Global Warming Potential; HA Habitat Alteration; HH Human Health; HHC Human Health Cancer; HHNC Human Health non Cancer; HTP: Human Toxicity Potential; IR Ionizing Radiation; LO Land Occupation; M Minerals; MAETP: Marine Aquatic Eco-Toxicity Potential; ME Mineral Extraction; N-Car Non-Carcinogens; NRE Renewable and Non Renewable Energy; NRCED Non-renewable Cumulative Energy Demand; NRE Non-Renewable Energy Consumption; NRPEC Non- Renewable Primary Energy Consumption; NRW Non-Radioactive Waste; O Odor; OCE Operational Carbon Emissions; OLDP Ozone layer Depletion Potential; OE Operational Energy; PED Primary Energy Demand; PMF Particulate Matter Formation; POCP Photochemical Ozone Creation Potential; Ra Radiation; R Resources; RI Respiratory Inorganics; RO Respiratory Organic; RPEC Renewable Primary Energy Consumption ; RW Radioactive Waste; S Smog; SW Solid Waste; TA/NP Terrestrial Acidification/Nutrification Potential; TETP Terrestrial Eco-toxicity Potential; W Waste; Water Intake; WC Water Consumption; WD Water Depletion. 19 4.3. Analysis of the life cycle stages and scenario definition Among the selected papers, it was detected that none of the cases included all modules. Reduction of stages and modules depended on the aim of the study. The major reductions were detected in use, demolition, and loads and benefits stages. In that respect, 30% of cases studies omitted two or more LCA stages. Utama et al. [34], compared direct and indirect emissions of building envelope materials on product, construction and maintenance modules. Houlihan et al. [43] calculated environmental impact of complete building considering production, maintenance and operational energy and water. Iddon et al. [39] compared four different construction scenarios for a typical house including production and operational energy use. Rossi et al. [38] compared embodied and operational consumption for a house in three different European locations by considering production, transport to site, operational energy and water use. Rosselló-Batle et al. [60] also compared embodied and operational energy demand in a Mediterranean climate by including production stage, maintenance –partially- and operational energy. Several omitted modules were justified by previous research. Furthermore, more than 70% of papers included all LCA stages within system limits -production, construction, use and demolition-. Gervasio et al. [42] introduced an LCA application for early stages of design. The study is the most complete case; it included almost all modules, except A5, B1 y B7. Lewandowska et al. [36] became one of the most complete cases, by including: A2-A5, B1, B2, B3, B4, B6, B7, C1, C2 and C4. Islam et al. (2014) included: A1-A5, B2, B4, B6, C1 and C2. Dahlstrøm et al. [41] included: A1-A5, partially B2 (just for ventilation and heating systems), B6, B7, C1 and C3. Hanandeh [32] included all LCA stages: production, construction, operational stage –just B2, B6, B7- and recycling – just for aluminum windows and frames. Babaizadeh et al. [31] omitted A5, B1-B5 and B7. 4.3.1. Analysis of the production stage Production stage was included in all the selected papers. It referred to the phase that data collection is more accessible than use or end of life phase. Table 3 demonstrates that it was the phase where generic database or other sources were mostly used. 4.3.2. Analysis of the use stage Use stage was the most heterogeneous phase in terms of module assessment; none of the selected papers had totally considered this. Operational energy use was included in 95% of cases, while replacement, refurbishment and repair were hardly included. It was confirmed that the use stage had the most uncertainties in 20 data collection, because of the lack of data bases, statistics or any other criteria that simplified the process. According to Table 3 data sources about the use stage were mostly based on the authors´ estimations. 21 1 Table 5. Comparison of life cycle stages considered on reviewed papers. Building life cycle information Suppletory Information beyond Build. life cycle A1-A3 Product stage A5-A6 Construction stage B1-B7 Use stage C1-C4 End of life stage D Benefits / Loads Reference A1 Raw material Supply A2 Transport A3 Manufacture A 4 Transport A 5 Cont. instalation proc. B1 Use B2 Maintenace B3 Repair B4 Replacement B5 Refurbishment B6 Operational energy use B7 Operational water use C1 Demolition C2 Trasnport C3 Waste processing C4 Disposal D1 RE-use recovery recycling potential 1. European Cases Houlihan et al., 2014 X X X - - - - - X - X - - - - - - Gervasio et al., 2014 X X X X - - X X X X X - X X X X X Dahlstrøm et al., 2012 X X X X X - X - - - X X X X X - - Motuzienè et al., 2016 X X X X X - X - X - X X X X X X - Proietti et al., 2013 X X X X X - X - - - X - X X X X (X) Takano et al., 2015 X X X - - - X - X - X - X X X X X Cuéllar-Franca & Azapagic, 2012 X X X X X - X - X - X X X X X X X Iddon et al., 2013 X X X - - - - - - - X - - - - - - Monteiro & Freire, 2012 X X X X X - X - X - X - - - - - - Rosselló-Batle et al., 2015 X X X X - - - - - - X - - - - - - Lewandowska et al., 2013 - X X X X X X X X - X X X X - X - Rossi et al., 2015 X X X X - - - - - - X X - - - - Fouquet et al., 2015 X X X X X - - - - X X - X X X X - Peuportier et al., 2013 X X X X X - X - - - X X X X - X - 2. Non- European Cases Babaizadeh et al., 2015 X X X X - - - - - - X - X X X X X Utama et al., 2012 X X X X X - X - X - - - - - - - - Hanandeh, 2015 X X X X X - X - - - X X - X - X X Islam et al., 2014 X X X X X - X - - - X - X X - - - Oyarzo & Peuportier, 2014 X X X X X X X X - - X X X X X - - 3. European and Non- European cases Mosteiro-Romero et al., 2014 X X X X X - X - X - X - X X X X X 22 4.3.3. Analysis of the end of life stage End of life stage was omitted in 20% of the case studies, and several strategies were detected. Peuportier et al. [61], for instance, assumed landfill for demolition waste as a way for simplifying end of life stage definition. Fouquet et al. [62] defined two scenarios for a timber frame system, comparing incineration and landfill. Babaizadeh et al. [31] also described different scenarios for building materials: 75% of wood is assumed to be used for landfill, the rest 25% is incinerated, and aluminum and PVC is assumed to be recycled. On the other hand, Monteiro & Freire [63], justify the end of life omissions by considering the limited importance of end-of-life stage impacts in South European single-family houses, demonstrated in Nemry et al. [104] . 4.3.4. Analysis of the benefits and loads Benefits and loads were hardly included. Several cases included partial accounts. Hanandeh [32] for example considered benefits only for aluminum windows and frames. Other cases justified the omission. Dahlstrøm et al. [41] assumed the worst-case waste scenario, so no gains from reuse or recycling material were considered. 5. DISCUSSION Reference literature [9,29] assumes that simplifications to LCA referred to system boundary definition, data acquisition and results communication. Therefore, simplifications of the LCA method refer to reducing and optimizing those aspects. Based on that fact, from publications analyzed the following issues are discussed: strategies that search to reduce the amount of data and processes – Study of object boundary-, strategies that search to optimize life cycle stages and scenario definition -Life cycle stages and scenario definition-, and finally, strategies that search to simplify impact calculation and result communication -Impact calculation and results communication-. 5.1 Study of object boundary The study of object definition involves setting limits to real building. Detected simplification strategies are mostly focused on reducing the amount of data, optimizing data collection and simplifying LCA. According to EN 15978 [13] system boundaries and functional unit definition do not only refer to complete building application, it also allows for partial assessment of buildings, e.g. building envelope, windows, roofs, etc. So, that reduction is considered as a simplification strategy. Among papers reviewed, 35 % of partial or reference 23 area applications are detected. Babaizadeh et al. [31] focus the study on shading assessment. Gervasio et al. [42], for instance, develop a macro–component approach. Dahlstrøm et al. [41] reduce the functional unit to a 1m2 of useable floor area. Papers analyzed show growing interest in using BIM for developing the physical model of the building [3,39,43]. [3] Although, Houlihan et al. [43] recognize the existence of several limitations in calculation of some building components, it demonstrates that BIM is a helpful format for quantifying material inputs. The lack of data sources and the complexity in modelling building processes –such as transport, maintenance, repair, refurbishments, demolition, waste treatment or recycling-, is simplified in most cases as estimations based on previous research or regional data sources. 5.2 Life cycle stages and scenario definition The review demonstrates that life cycle stages definitions also play an important role to simplified LCA for single-family houses. Among papers analyzed, no complete modules–A1 to D- assessment is detected. So according to the EeB Guide [14] type classification, most of the cases correspond to Simplified LCA application type. The review also demonstrates the relevance of product stages and operational energy use module in LCA for single-family houses. Product stage (A1 to A3) is included in all cases and Operational energy consumption (OE) is also mostly considered. Cuellár-Franca & Azapagic [37] show that it represents about 90% of GWP. Regarding case studies, reduction and simplification in life-cycle stages, these are related to the scope and objectives of each case. According to Houlihan et al. [43], Iddon et al. [39], Rossi et al. [38], Rosselló-Batle et al. [60], if the assessment is focused on comparing embodied and operational impacts, life-cycle stages definition is centered on product stages and energy consumption during use module. In other cases [3,31– 33,35,36,40,41,44,45,62,61,105], if the assessment is focused on environmental impact during the life-cycle; product, construction, use and demolition are mostly included, while loads and benefits are hardly considered. It is also detected in Gervasio et al. [42] that early stages of design assessments are focused on products, construction, use –partially-, and demolition stages. Utama et al. [34] center on building material performance; product, construction and use are partially considered. Furthermore life cycle stages and scenario definitions are heterogeneous in all case studies. Product stages scenario is mostly recognized to be supported by generic databases as shown Table 4. However, EN 24 15798 [13] assumes the use of EPD as a simplification to product stage scenario definition. Among papers reviewed no EPD applications are detected. Use stage scenario definition is directly related to construction materials, climate, technology, and other regional characteristics. Simplification strategies aim to facilitate access to uncertain information. In this context, most of the papers considered are based on the authors’ estimations or previous research as shown in Table 4. Moreover, the use of Dynamic Thermal Simulations tool to help on Operational energy use scenarios definition is widely recognized. End-of-life stage was one of the most heterogeneous stages. Detected simplification strategies assume in several cases landfill, justified omission, or incineration, as an alternative for a waste treatment scenario. In spite of that fact the European context goals by 2020 aim to reuse, recycle or recovery of material of at least 70% of non-hazardous construction and demolition waste [106]. 5.3 Impact calculation and results communication Results demonstrate that depending on Impact calculation methods, final results can differ. Moreover, calculation methods are defined based on selected environmental impact indicator. Monteiro & Freire [63] demonstrate the influence of Impact calculation methods in LCA results. The study, that compares three of the most used calculation methods –CML, Ecoindicator´99 and CED-, demonstrates that by using these methods inconsistent results can be obtained for HTP, ET and PODP. So, the study suggests that LCA for single-family houses ought to include multiple environmental impacts and ought not to include toxicity categories. Several cases have cut down the number of impact indicators by considering different criteria as: regional representativeness, global impact, embodied vs operational impact, renewable vs non-renewable energy consumption. From the analysis of the selected papers it is demonstrated that this simplification strategy can reduce the amount of data and complexity in LCA application, without altering result comparability. According to the selected papers GWP is the most significant environmental indicator; globally recognized as one of the most significant indicators for climate change mitigation strategies, and also takes part of the EN 15978 [13] required environmental indicators. Almost 20% of case studies [33,35,62,105] that considered complete building as the functional unit have calculated and included GWP results in the paper. Those cases were compared in Fig. 2, in spite of the fact that methodological differences between them are recognized. Fig. 2 summarized the GWP ratio (kg. eq. CO2/m2/yr.) obtained from selected cases studies. According to Fig. 2 results obtained are heterogeneous. Only two cases [33,105] considered similar service lifetime (50 years), similar life cycle stages and the same impact calculation method (CML 2001 method). For these cases, the GWP 25 ratio ranges from 23 to 105 kg. eq.CO2/m2/yr. and the media value for typical or reference scenario was 57 kg. eq.CO2/m2/yr. Fig. 2. Comparison of GWP ratio (kg. eq. CO2/m2/yr.) from selected case studies [Selected case studies: Cuéllar-Franca & Azapagic: C-DE, detached house; C-SD, semi-detached house; C-TH terraced house; Monteiro & Freire: M-H0, reference house with double hollow brick masonry; M-H1 reference house with double facing and hollow brick masonry; M-H2, reference house with light weight concrete block masonry; M-H3, reference house with thermal concrete blocks masonry; M- H4, reference house with autoclaved aerated concrete block masonry; M-H5, reference house with hollow brick masonry & ext. wood cladding; M-H6, reference house with wood frame and cladding; Fouquet et al.: F-OBL, reference house considering timber frame landfill scenario; F-OBI, reference house considering timber frame incineration scenario; F-DM, reference house with concrete blocks cavity walls; F-BB, reference house with cast concrete walls; Oyarzo & Peuportier: O- PA1, reference house in Punta Arenas; O-PA2, regulatory house in Punta Arenas; O-PA3, improved house in Punta Arenas; O-PM1, reference house in Puerto Montt; O-PM2, regulatory house in Puerto Montt; O-PM3, improved house in Puerto Montt; O-S1, reference house in Santiago; O-S2, regulatory house in Santiago; O-S3, improved house in Santiago; Mosteiro- Romero et al.: M-US, LEED-H certified house in US; M-SW, Minergie-P certified house in Switzerland]. 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[106] European Commission, Directive 2008/98/EC of the European Parliament and of the Council on waste and repealing certain Directives, 2008. 36 Highlights:  Review of recent single-family houses LCA, focused on simplification strategies.  Simplification mainly focused on system boundary and results communication.  The most considered environmental impact indicator was GWP.  Future studies need simplification strategies that allow results comparability.