Introduction

Research framework and limitations

In most post-industrial European countries, including Switzerland, enabling sustainability transition of the built environment by reducing its environmental footprint is a priority. Considering energy consumption in their daily life, Swiss households appear as highly energy demanding due to materials needed for the building construction, to the dwelling operation and to the induced mobility (Novatlantis et al. 2011). Based on the ‘2000-W society’ vision (Suisse Energie 2017), Switzerland has updated its energy strategy aiming at sustainable use of resources (SFOE 2015a). Within the context of this vision, by 2100, the annual global warming potential (GWP) indicator is limited to 1 ton of CO2 equivalent (CO2e) per person and a maximum primary energy (PE) power of 2000 W per person, including 500 W of non-renewable primary energy (NRPE). This represents a reduction of 88% GWP and 78% of PE with respect to 2005 when the mean power per person was about 6000 W. In 2014 and 2015, it was already reduced to less than 5000 W (Suisse Energie 2017). Swiss authorities (SFOE 2015a; SIA-2040 2017) have defined intermediate targets for 2050 for the built environment, which consider a broad environmental assessment of the building, including its construction and operation, as well as the occupant-induced mobility.

The conducted literature review highlights the lack of reference data concerning the environmental impacts in terms of non-renewable primary energy consumption and global warming potential owing to the construction process, the use of the dwelling by occupants and their induced daily mobility in Switzerland (Jusselme et al. 2015). Considering the growing impacts of materials, which can account up to 40 to 60% of the global environmental impacts of energy-efficient buildings, conducting detailed assessments of embodied impacts is urgent (Sartori and Hestnes 2007; Cabeza et al. 2014). Nevertheless, data of construction material impacts emerge from analysing the building scale (SIA-2032 2010) and depend on specific building features (Gustavsson and Joelsson 2010). For that reason, it is difficult to find average and reliable reference values per square meter of dwelling or based on site-specific climate and applicable on a large scale to assess a whole set of buildings (John 2012; Hoxha et al, 2016a).

Preliminary studies and remaining challenges

The paper directly addresses limitations detected in a preliminary step of the research, which conducted an energy assessment of the dwelling stock of urban centres, suburbs, peripheries and rural areas and questioned the theoretical capacity of Swiss dwellings to achieve the energy performances required by the 2000-W society vision (Drouilles et al. 2017). Based on the analysis of statistics and literature, the previous study highlighted the limitations of conducting large-scale energy assessments.

Aguacil et al. (2017a) summarize both possible approaches to conduct an energy assessment or life-cycle assessment (LCA), at large-scale (top-down or bottom-up) and expose their main applications. The top-down approach is based on real energy consumption of a large area (i.e. city or country) provided by energy suppliers. Based on global data, this approach tries to estimate the energy consumption of a specific area (e.g. a neighbourhood); the global consumption is proportionally attributed to the chosen measure unit (built area, dwelling, building types) (Steskens et al. 2015). The bottom-up approach begins with a detailed study at building scale (using representative buildings). It consists of analysing the construction details to obtain specific energy consumptions using simulation software. The environmental impacts are calculated based on the energy simulation results and the study at the level of constructive detail. The energy assessment of a specific area, i.e. composed of different buildings classified in representative buildings or archetypes, proceeds from upscaling results obtained at building scale. Through this upscaling process, by multiplying the results by the total number of buildings, dwellings or square meters of the studied area (Swan and Ugursal 2009), it is possible to estimate the energy consumption and global warming potential of a wider building stock fitting the archetype features.

Most of the existing research aiming to assess energy performance at the scale of built areas implement either large-scale modelling (Ratti et al. 2005; Stephan et al. 2012) or statistical analyses based on household consumptions (Holden and Norland 2005; Rey et al. 2013). Therefore, the results depend on the studied area and are usually focused on final energy consumptions. Since specific building features are necessary to make these calculations, this kind of approach can assess neither the primary energy consumption nor the embodied impacts owing to the building construction.

The Typology Approach for Building Stock Energy Assessment (TABULA) project (IEE 2016), involving twenty European countries, has focused on the elaboration of a harmonized database of existing buildings to allow energy assessment of the building stock (Loga et al. 2016). Unfortunately, TABULA only focuses on operational energy consumption and the database applies to countries part of the European Union, which does not include Switzerland. Other researchers have limited the study boundary to only one material (Kunič 2017), one built element (Slavkovič and Radivojevič 2015), one case study (Citherlet and Defaux 2007; Paganin et al. 2017) or a specific area (Xu et al. 2016). None of them has studied buildings in their totality, including also different locations through the variable impacts of daily mobility. Research focussing on European countries highlights the influence of considering specific climate conditions using hourly weather data in the simulation process to evaluate properly the dwelling operational impact and the embodied impacts (Rossi et al. 2012; Aguacil et al. 2017a). Hence, an adequate database built within a specific context is required to conduct a reliable LCA.

At large-scale, research on energy consumption tends to focus mainly on dense urban areas. Nevertheless, some authors have started to assess the energy performance of peripheral residential areas in order to evaluate the effect of centrality on the overall energy balance (Heinonen et al. 2013a; Rey et al. 2013; Ottelin et al. 2015). The main factor that conditions the variation of the overall energy performance is the daily mobility of the inhabitants (Rickwood et al. 2008). In a context of increased concentration of equipment, services and activities in urban centres, the inhabitants of the urban periphery rely on commuting to access work and leisure places. The energy and environmental impacts of induced daily mobility represent a considerable cost for households (Desjardins and Mettetal 2012; Drouilles et al. 2017). New developments about these questions consider the occasional mobility related to holidays (Nessi 2012; Munafò 2016) because it implies a rebalancing of travelled distances between centre and periphery (Holden and Norland 2005). However, the direct effects are unclear since mobility practices are also highly dependent on lifestyles, which are spread unevenly among each territorial entity (Heinonen et al. 2013a, b).

Overview of the study

The research described in this article tries to overcome the identified limitations by generating a reliable methodology adapted to the Swiss dwelling stock in order to conduct large-scale life-cycle assessments. It aims at exploring some possible evolution strategies of the residential building stock according to a variety of representative features. The novelty of this research lies in expanding the boundary of common studies by evaluating the environmental performance of buildings (construction and operation) and induced mobility. Not only does it assess the related environmental impacts for a singular building, but it also takes into account several energy performance objectives, construction typologies, energy sources and heating, ventilation and air-conditioning (HVAC) and domestic hot water (DHW) systems, and it also assumes different locations, private parking types and assessment horizons for evaluating induced daily mobility aspects. As a result, this research provides new reference data available for strategic planning with a twofold perspective. First, it can inform decision-makers, government or non-government organizations on where to put their efforts while developing solutions with low environmental impacts. Second, it can provide an assessment framework to conduct LCA at the neighbourhood or city scale based on the combination of several alternative scenarios.

The methodology follows a systematic way for the database to become as informative and reusable as possible. It uses the concept of archetype that defines a theoretical model able to represent each of the different building typologies of specific building stock (Oliveira Panão et al. 2013). Hence, according to the Swiss housing stock current constitution, the study considers four residential archetypes: single- and multi-family buildings, implementing both new and renovation projects. Afterwards, the method consists in analysing and comparing scenarios and variants of each archetype by considering the whole LCA according to the 2000-W society vision framework. Environmental impacts, expressed in terms of non-renewable primary energy (NRPE) and global warming potential (GWP), first relate to the operation of buildings and of induced motorized daily mobility depending on location and building type. Then, they consider the construction materials on a lifespan of 60 years. The definition of variants includes (1) energy performance objectives, (2) construction typologies, (3) energy sources and HVAC/DHW systems, (4) induced daily mobility assuming two different performances of motorized conveyances and (5) private parking types (Fig. 1).

Fig. 1
figure 1

Synthesis of scenarios and variants for the estimation of the environmental impact of the four archetypes

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‘Material and method’ presents the chosen residential archetypes based on the analysis of territorial organization and composition of the housing.

Material and method

Selection of residential building archetypes

The method chosen to analyse the existing building stock implements a bottom-up approach. The strength is to consider a specific building in order to estimate in a more accurate way its non-renewable primary energy and the resulting global warming potential for (1) material and construction (embodied impacts), (2) use of the building (operation impacts) and (3) daily mobility of building users (operational impacts owing to the induced daily mobility). The remaining issue consists in choosing some buildings representative of the Swiss housing stock to provide a valid and reliable reference framework.

Sustainable urban planning raises many challenges in terms of building retrofit or construction of energy-efficient new buildings, which has been tackled by abundant research on low energy construction (Ruiz et al. 2012; Lasvaux et al. 2017). According to available data from the Federal Statistical Office (FSO), the share of new dwellings in the Swiss building stock was 1% in 2015. However, it differs between the stock of single-family houses—0.96%—and the multi-family houses one—1.45% (FSO 2017a). Following this trend, 65% of the 2050 building stock already exists. Therefore, in order to follow the guidelines set by the intermediate targets for the horizon of 2050, it is necessary to take into account not only new-construction projects but also the retrofit potential (Eames et al. 2013; Jones et al. 2013; Riera Pérez and Rey 2013).

Single- and multi-family houses represent about 82% of the Swiss dwellings and buildings (FSO 2017a) (Table 1). The remaining 18% gather mainly mixed-use buildings (residential and non-residential). The two periods of 1946–1979 and 1980–2015 gather 70% or more of the residential building stock. This threshold is interesting as new policies have targeted, since the 1980s and in response to the oil crises, a reduction of energy consumption in new buildings, through improving building envelope, increasing insulation and implementing double-glazing windows (SFOE 2015b).

Table 1 Number of buildings and dwellings for single- and multi-family houses in 2015 in Switzerland, per construction period. Source: FSO 2017a
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To be representative of the existing residential building stock, this study proposes four archetypes: both types of residential buildings (single- and multi-family houses) of two construction periods (existing buildings to be refurbished and new constructions) to reflect the evolution of practices. The chosen archetypes for the existing building to be refurbished (called SFH.r and MFH.r) consider the construction features of the 1940s–1970s, according to the eREN research project (HEIA 2016). New buildings (named SFH.n and MFH.n) are designed according to the common example found nowadays in Switzerland. Table 2 sums up the main features of the four residential archetypes.

Table 2 Main features of the four residential archetypes: single-family house–new (SFH.n), single-family house–retrofit (SFH.r), multi-family house–new (MFH.n) and multi-family house–retrofit (MFH.r)
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Scenarios definition

To clarify the number of simulations, Fig. 1 shows in a schematic way the combinations of the different parameters for each archetype (SFH.r, SFH.n, MFH.r, MFH.n) and synthesizes each scenario and variant with the codification used in this article. The different energy performance scenarios are based on variable features and targeted performances. In this scope, we used Swiss regulation and labels as a reference framework to set energy performance targets. Scenario E0 represents the current pre-renovated status of the 1950s–1970s buildings (including double-glazing windows). Scenario S0 represents the baseline, for which the building performance is at least compatible with the current Swiss regulation SIA 380/1 (SIA 2016b). Scenario S1 uses the requirements set by the MINERGIE® label as performance targets. Scenarios S2 and S3 respectively follow at least the requirements of MINERGIE-P® and MINERGIE-A® labels commonly used in Switzerland (Hall et al. 2014; Minergie 2017).

The strategies for improving the building envelope (e.g. insulation thickness, fenestration type) are defined in order to achieve the different performance targets of each scenario (S0, S1, S2, S3). Afterwards, several inflexion parameters imply the elaboration of a series of different variants. They are related to:

  1. 1.

    Considering different construction systems, common practice (cp.) or best practice (bp.), including variations of material quality, insulation thickness (affecting U-values), façade finishing, etc.

  2. 2.

    Considering different HVAC and domestic hot water (DHW) systems from an oil boiler to an electric heat pump

  3. 3.

    Increasing the use of renewable energies by the implementation of solar thermal (ST) or photovoltaic panels (PV)

  4. 4.

    Adjusting the results of embodied impacts according to the parking type: underground parking, individual garage and outside parking

  5. 5.

    Considering five locations: urban centres, suburban, peri-urban, rurban and rural areas (Drouilles et al. 2017)

  6. 6.

    Considering, for the mobility aspects only, two hypotheses to include current performance and assumptions about the future improvements of mobility technologies achieved by 2050 (SIA 2016a)

Regarding the energy source to cover heating and DHW demands, FSO provides data about the repartition per type of buildings and construction periods (FSO 2017b). According to the data in Table 3, oil is by far the most spread heating energy source in buildings. About 70% of all residential buildings, from the 1940s–1970s period, use oil boilers. Since 1980, oil is still the principal heating energy source along with natural gas and electric heat pump. Hence, scenarios E0 and S0 use oil for heating and DHW, and scenarios S1 to S3 implement heat pumps as it is the major heating system installed in certified MINERGIE® (–, P, A) buildings, for both new and retrofit projects (Minergie 2017). This broad use is due to the simplicity of the installation, the low-level of energy demand and the good combination with on-site energy production.

Table 3 Energy sources used for heating (representation higher than 3%) by building type (FSO 2017b)
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Retrofitting approach

The existing single-family house archetype—SFH.r (Figs. 1 and 2a)—has been defined according to Swiss buildings and housing statistics (FSO 2017a), and real estate information. The house is composed of three storeys. Living areas are situated on the ground and first floors, while the underground floor is an unconditioned area.

Fig. 2
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Main façade section for 1940s–1970s archetypes in their current status E0. (a) SFH.r. (b) MFH.r

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The existing multi-family house archetype—MFH.r (Figs. 1 and 2b)—has been adapted from a real six-storey building built in 1968 in Neuchâtel. The semi-underground level has unconditioned non-residential spaces.

For the energy retrofitting projects, we relied on the eREN research project to define the archetypes proposed in this article (HEIA 2016). The most common wall type of buildings from 1940s–1970s is a 20-cm brick wall without thermal insulation. The outer layer of the façade is roughcast plaster. Horizontal slabs are built in reinforced concrete. The roofs are sloped (wooden structure) or flat (concrete structure) and not insulated. The windows present double-glazing and a wooden frame without thermal bridge rupture (Fig. 2a, b).

Retrofitting variants S0 to S3 qualified as common practice implement a traditional and affordable construction system, with most commonly used material and methods in Switzerland (HEIA 2016; SFOE 2017). An external insulation façade system is implemented on the existing façade. According to the energy performance target, each scenario implements a specific thickness of insulation using expanded polystyrene (EPS) for roof and façade. The renovation includes the replacement of the frame and glazing of existing windows (Fig. 3a, b).

Fig. 3
figure 3

Section of the main façade for 1940s–1970s archetypes, applicable for common practice variants: S1.cp, S2.cp and S3.cp. (a) SFH.r and (b) MFH.r (*ST or photovoltaic panels)

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Qualified as best practice, retrofitting variants (S0.bp to S3.bp) seek to implement a lighter and low-impact construction system based on wood with an external insulated ventilated façade (with 100% recycled EPS, wood structure and solid panels) (Fig. 4a, b). Wooden frame with thermal bridge rupture windows is installed with improved U-values, from 0.98 to 0.7 W/m2 K depending on the scenario.

Fig. 4
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Section of the main façade for 1940s–1970s archetypes, applicable for best practice variants: S1.bp, S2.bp and S3.bp. (a) SFH.r and (b) MFH.r (*ST or PV panels)

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New construction

According to statistics (FSO 2017a) and the trend of Swiss single-family house design, through the comparison online projects (Bautec SA, Mistral construction SA, Prologis Sàrl, Renggli AG, Villvert SA), the single-family house archetype—SFH.n (Figs. 1 and 5)—is a two-storey building with flat roof, which design avoids openings on the north façade.

Fig. 5
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Section of the main façade for new construction archetypes. (a) Common practice variants—S1.cp, S2.cp and S3.cp. (b) Best practice variants—S1.bp, S2.bp and S3.bp (*ST or PV panels)

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Statistics (FSO 2017a) and Swiss construction current practice gave the design framework for the multi-family house archetype—MFH.n (Figs. 1 and 5). The design seeks compactness, air tightness, good day lighting potential and natural ventilation. The entrance level is situated on a semi-buried floor, with non-residential uses.

Qualified as common practice, the proposed construction system follows the one of retrofitting variants and implements bricks for all bearing walls and reinforced concrete for all horizontal elements including the flat roof. A roughcast plaster protects external insulation (EPS). The partitions are built with a plasterboard sandwich system with metallic structure and acoustic insulation (rock wool) (Fig. 5a).

The variants qualified as best practice implement a wooden construction system for each horizontal and vertical elements of the building (Fig. 5b). The insulation also has a lower environmental footprint, being 100% recycled EPS.

For the current status (E0), the existing HVAC system is maintained without implementing renewables. For baseline scenario S0, an oil boiler is considered in addition to solar thermal panels to cover about 30% of DHW demand. For scenarios S1 to S3, an electric heat pump system partially fed by a photovoltaic installation is proposed. Regarding the energy performance simulations, the coefficient of performance (COP) is of 0.85 for the oil boiler and of 2.8 for the electric heat pump system. It includes the losses due to supply elements (wall radiators) and facility distribution.

Private parking places

Apart from the material associated with the renovation of existing buildings or new construction, the calculation of embodied impacts includes the construction materials of different parking types. The single-family house archetypes include two parking places. For multi-family houses, one place per dwelling plus 10% for visitors is counted on average. As shown in Fig. 1, three types of parking places are assessed: (1) underground parking, (2) individual garage and (3) outside parking. The type of outdoor flooring differs according to the construction quality: Asphalt is implemented in common practice scenarios, while a prefabricated concrete mono bloc paving is used in best practice variants.

Energy assessment framework

Calculation method and targets

According to the Swiss regulation for buildings (SIA 2015b), energy requirements are evaluated based on the energy reference area (AE). AE considers all living and conditioned areas within the thermal envelope of a building including all construction elements, i.e. it is measured from the external perimeter of the considered area. As a result, AE changes according to the wall thickness. The impact is significant for new buildings, in particular between common practice and best practice variants (Table 4).

Table 4 Energy reference area (AE) for each scenario depending on the construction variant (common practice or best practice) and its level of insulation
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To define a comparison basis to assess the performance of each scenario, the study considers the intermediate targets set by SIA-2040 (2017) for 2050, in the framework of the 2000-W society vision (Novatlantis et al. 2011). Table 5 presents the targets for residential buildings in terms of non-renewable primary energy (NRPE) and global warming potential (GWP).

Table 5 Intermediate targets for 2050, including environmental impacts related to the operation, the construction and the induced daily mobility, expressed in non-renewable primary energy (NRPE) and global warming potential (GWP) SIA-2040 (2017)
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Environmental impacts

Embodied impacts are assessed according to the European standard (EN-15978 2012) for an assumed building reference study period of 60 years (SIA-2040 2017). The functional unit of a square meter of energy floor area AE (m2 year) is considered for the assessment of the non-renewable primary energy consumption and global warming potential indicators. The boundary of the whole building LCA includes stages of production, construction, use and end of life. The hypotheses for transport distance, construction and building elements lifespan used for the assessment of the embodied impacts are similar to those presented in Hoxha et al. (2016b). Environmental impacts of construction stage for different previously described macro components are evaluated based on the corresponding quantity employed in each scenario and on impact factors of theKBOB database (KBOB 2016). This database contains information about the environmental impacts of building materials for the Swiss context and is in accordance with the CEN standard (EN 15804 2012). The transport of building elements and components to the construction site is made by truck (16-32t) for an assumed distance of 50 km. Within the boundary of the assessment is also considered the environmental impact of building components replacement—according to their assumed service life (Hoxha 2015). The impacts of end-of-life stage are evaluated in accordance with the Swiss practice translated in the KBOB database.

The assessment of the operational impacts is based on final energy consumption for heating, cooling, DHW, lighting and appliances that are evaluated following the Swiss regulation for buildings SIA-380/1:2016 (SIA 2016b). The simulations rely on a definition of the building envelope using an iterative process through hourly-step simulation using Energy Plus (DesignBuilder Software v.5 2018) and Neuchâtel region weather file generated using Meteonorm software (Remund et al. 2010; Meteonorm2017). The energy model has been configured using the normative assumptions and user profiles for multi- and single-family buildings provided by the SIA 2024:2015 (SIA 2015a), including occupancy schedules and standard utilization profiles. Using these normative assumptions, the results can be compared with the 2000-W society targets for 2050 defined by the SIA 2040 (SIA 2017).

Performance targets of the scenarios depend on the building size and the average temperatures in their location. For scenario S0, according to the SIA-380/1:2016 (SIA 2016b), the target is fixed on a limit of heating energy demand (Qh,li) that takes into account the energy reference area (AE) and thermal envelope area (Ath).

$$ Qh, li=\left(13+15\cdotp \frac{A_{th}}{A_E}\right)\cdotp fcor $$
(1)

where

$$ fcor=1+\left(9.4- AMT\right)\cdotp 0.06 $$
(2)
Qh,li:

Limit of heating energy demand (kWh/m2 year)

A th :

Thermal envelope area (m2) evaluated according to SIA 380 (2015b)

A E :

Energy reference area (m2) evaluated according to SIA 380 (2015b)

fcor:

corrector factor related to the weather of the building location, and calculated with formula 2 (ø)

AMT:

real annual mean temperature of the building location (9.7 °C for Neuchâtel (Switzerland)) (°C)

Scenarios S1, S2 and S3 are designed to be compatible with MINERGIE® (–, P, A) labels. Within this framework, the energy performance targets take into account the whole energy balance of the building expressed in final energy in kWh/m2 year (Table 6). According to the requirements set by MINERGIE® (–, P, A) labels, installing a minimum of 10-W peak of photovoltaic (PV) power per each square meter of energy reference area is mandatory in new buildings. The scope of the study not being on the implication of PV installation, the resulting PV production—the self-consumption part only—is accounted for in the final energy results. The assumption is that the PV production reduces the energy consumption of lighting, appliances and HVAC using an electric heat pump.

Table 6 Final energy limit consumption for S1–S3 scenarios, for new and renovation projects (MINERGIE 2017)
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Induced daily mobility operational impacts

The technical specification SIA-2039 (2016a) provides a calculation framework to assess the environmental impacts owing to induced daily mobility. The document presents two methods to estimate the energy needs related to daily mobility of building occupants, whether the current mobility and location are known. When neither is known, the method relies on FSO’s micro-census on mobility and transport (FSO and ARE 2012), which represents the most complete data source about mobility practices in Switzerland.

Within our archetype model, mobility and location are unknown. Hence, we looked for a way to attribute mobility values by building type and territorial entity. Based on a classification of Swiss municipalities between centre, suburban, peri-urban, rurban and rural areas (Drouilles and Rey 2018), we analysed the micro-census results and obtained a repartition of travelled distances and transportation types per territorial entities (FSO and ARE 2012). Induced daily mobility considers only incoming mobility. In the case of residential buildings, 47% of daily mobility is counted SIA 2039 (2016a).

This calculation method questions the integration of the impacts due to the construction and availability of parking spots in a residential project. According to SIA-2039, ‘the primary energy consumption clearly increases if parking places are available’ because the use of individual motorized transport is easy. Data from the micro-census are dependent on households’ characteristics rather than on buildings’. Hence, the presence of parking places affects neither the results of travelled distances nor the conveyances repartition. This is one limitation of this approach. In further work, the implantation of the modelled building on a specific existing plot should allow the assessment of environmental impacts owing to daily mobility of inhabitants in a more precise way.

The method to estimate these impacts considers, in addition to territorial entities, the housing occupancy status (‘tenant’, ‘house owner’, ‘apartment owner’ and other less representative types). Crossing those results with the repartition of housing occupancy status by territorial entities, specific mobility data came out for single- and multi-family houses as well as for each territorial entity. Table 7 shows the repartition between occupancy status and territorial entity. It also provides the daily travelled kilometres. The daily mobility is highly influenced by the repartition of owners and tenants, which is inverted between single- and multi-family houses. Distances also tend to be longer in peripheral areas.

Table 7 Daily mobility, individual motorized transport (IMT), public transport (PT) and soft mobility (SM) data for induced daily mobility estimation, according to the location and the type of user (owner or tenant)
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Table 7 also shows conveyance shares. The use of public transport and soft mobility is higher in central areas. The share of individual motorized transport, on the other hand, is higher in the peripheral and rural areas. Eighty-two percent of distances travelled by public transport use the train, while the rest (18%) resorts to buses and trams. SIA-2039 (2016a) provides conversion factors for each selected transportation mode, as well as reference values assuming future environmental impacts in the framework of the 2000-W society. As stated in (Drouilles et al. 2017), the current environmental impacts due to induced mobility are far from achieving the intermediate targets for 2050. Consequently, an alternative variant explores future potential impacts based on SIA’s hypothesis (Table 8).

Table 8 Conversion factors according to SIA-2039 (2016a)
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Conversion factors combine both operation and embodied impacts due to manufacturing vehicles and to building infrastructures. The estimation of conversion factors by 2050 relies on technologies and methods that already exist. Therefore, it is reasonable to think that these values will progressively decrease (Zachariadis 2006; Thiel et al. 2016). Regarding the individual motorized transport, SIA-2039 hypothesis for 2050 is 3 l of gasoline per 100 km. Regarding buses, the variant considers the implementation of cleaner and more efficient fuel (hydrogen and electricity). For trains, it implements more efficient technologies and thermal insulation to reduce air-conditioning demand (SIA 2016a). Considering the low impact of the embodied energy of soft modes (e.g. bikes) in comparison to other transportation types, they are not included in the assessment.

Results

Scenario performances with current induced mobility impacts

Environmental impacts of all assessed combinations, classified in three categories (embodied, operational and induced mobility impacts), are shown in Figs. 6 and 7 for non-renewable primary energy and global warming potential indicators. Graphs also include the reference value of the intermediate targets for 2050 to evaluate the specific performances of each scenario and variant.

Fig. 6
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Current induced daily mobility, operational and embodied impacts in non-renewable primary energy consumption (NRPE)

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Fig. 7
figure 7

Global warming potential (GWP) for current induced daily mobility, operational and embodied impacts

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Performance comparison

Regarding annual non-renewable primary energy (NRPE) consumption of the baseline scenario S0, the comparison of new building variants shows a reduction up to 36% between single-family houses (SFH.n.S0) and multi-family houses (MFH.n.S0). In the case of retrofitting scenarios, the NRPE consumption in multi-family houses (MFH.r.S0) is also about 37% lower than in single-family houses (SFH.r.S0). As a result of compactness and higher dwelling occupation, the retrofitted multi-family house located in the centre with individual garage (MFH.r.S0.cp.) is 23% more efficient than the corresponding single-family house (SFH.r.S0.cp.). For equivalent new constructions, the performance gap rises to 36%.

Although the overall results tend to be of the same magnitude, the performance results between retrofitting and new construction present different repartitions of energy consumption. The results emphasize the weight of embodied impacts in new construction scenarios. In the case of scenarios S1 to S3 applied to single-family houses, the embodied impact is nearly four times higher in new buildings than in retrofitting projects. However, new buildings tend to be more efficient in terms of operational impact: For S1, the performance of renovation project (SFH.r.S1) is 30% higher, compared to a new building (SFH.n.S1). Regarding scenario S2, the operational impact is also reduced by 52% from the renovation project (MFH.r.S2) to the new building (MFH.n.S2).

Results show that a new single-family house has a higher overall NRPE consumption than a house retrofitted to comply with the same energy standard. The performance gap between those archetypes varies from 5% (S1.bp) to 19% (S3.cp). For example, a new house of the variant SFH.n.S2.cp has an annual NRPE consumption of about 195 kWh/m2 year; the same variant achieved through retrofitting actions will reach an annual NRPE consumption of about 172 kWh/m2 year (12% lower). The results are not as clear regarding multi-family houses: Until S2, new buildings (MFH.n) perform better than renovation projects (MFH.r). Then, in scenarios S3, a retrofitted multi-family house (MFH.r.S3) is more energy efficient than a new one (MFH.n.S3). In terms of global warming potential (GWP), all retrofitting scenarios S1 to S3 present lower values both in single- and multi-family houses (SFH/MFH.r) than new buildings (SFH/MFH.n).

Results of the energy assessment for the retrofitting scenarios emphasize the performances of current construction standards in comparison with the current status of residential buildings (SFH.r.E0 and MFH.r.E0) constructed between the 1940s and the 1970s. Renovation projects of single-family houses according to the Swiss regulation (SFH.r.S0) achieve a reduction of 55% annual NRPE consumption, which goes up to 74% in the case of a house retrofitted to the highest energy standard (SFH.r.S3). Between single-family houses following the regulation (SFH.n/r.S0) and other SFH.n/r.S1–S3, a 30 to 40% reduction is achieved through increasing insulation and implementing on-site renewable energy production. Regarding multi-family houses, the NRPE consumption reduction is also significant but limited to 45% between current status (MFH.r.E0) and scenarios S0 (MFH.r.S0), or to 20 to 30% between (MFH.n/r.S0) and other (MFH.n/r.S1–S3).

Results of new buildings emphasize the weak performances of single-family houses. Unlike the other archetypes, none of the new variants of single-family houses (SFH.n) reaches any targets (Table 7). Retrofit actions highly affect the GWP and achieve reductions up to 85% between current status (SFH/MFH.r.E0) and S1 to S3 scenarios (SFH/MFH.r.S1-S3). Between the baseline S0 scenario and the following S1–S3, GWP indicator is reduced by 40 to 60%.

‘2000-W society’ vision as a demanding framework in Switzerland

The overall reading of the results implies that the intermediate targets are very demanding since only four variants out of 440 (1%) reach the non-renewable primary energy (NRPE) targets, and none of them complies with the global warming potential (GWP) targets. It is nevertheless encouraging that the retrofitted multi-family house (MFH.r.S3) achieves lower NRPE results than the intermediate targets, and 16 other variants are only less than 25% higher than the target. The results emphasize the impact of mobility results since the (nearly) complying results apply to variants located in the centre where travelled distances and use of individual motorized transport are lower (Tab. 7).

Building-related results

Detailed results in terms of operational impacts

This section focuses on the results in terms of energy consumed by electric appliances, lighting, heating and domestic hot water (DHW). Results presented in Fig. 8 show that complying with the Swiss regulation SIA-380/1 (2016b) offers a considerable reduction of non-renewable primary energy (NRPE) consumption and global warming potential (GWP). However, it is not enough to achieve intermediate targets for 2050 (Table 7). The most important reduction, up to 70% when considering GWP of SFH.r, is achieved between current status (SFH/MFH.r.E0) and scenarios complying with Swiss regulation (S0). Current regulation focuses on limiting the heating demand (according to formula 1 and 2, Environmental impacts section) and requires covering at least 30% of the DHW annual demand with renewables. The application of those requirements results in the greater energy performance of the building envelope and, additional implementation of ST panels (EnDK 2014) covers 4% of the NRPE consumption.

Fig. 8
figure 8

Results in terms of NRPE and GWP due to the final energy balance between consumption (electric appliances, lighting, heating and DHW). The results include the reduction due to renewable energy production (ST and PV panels), for each archetype and performance scenario, compared to the intermediate targets (Table 7)

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Regarding GWP, the shift to heat pumps and to more energy-efficient scenarios (S1 to S3) allows all scenarios to meet the intermediate targets. Regarding NRPE consumption, only S3 scenarios respect the targets, but only for three archetypes (SFH.r.S3, MFH.r.S3 and MFH.n.S3). To meet the targets for this indicator, the impacts of new single-family houses (SFH.n.S3) should still be reduced by 4%. This includes the reduction of the overall operational impacts thanks to self-consumption of renewable energy produced on site by photovoltaic (PV) installation in all S1–S3 scenarios. In new multi-family houses, for instance, the PV production allows a 14% (MFH.n.S1–S2) to 20% (MFH.n.S3) reduction of operational impacts.

Detailed environmental impact results

For common practice variants, the results presented in Fig. 9 show lower environmental impacts for retrofitting scenarios—only SFH.r.S3 does not reach the intermediate targets. The situation for new constructions is more disadvantageous since none of the variants reaches the targets for both indicators simultaneously. However, MFH.n.S0 scenario reaches the targets for GWP indicator. The environmental impacts of multi-family houses are lower than those of single-family houses. It confirms the positive shape effect in the minimisation of impacts.

Fig. 9
figure 9

Embodied impacts for common practice (cp) variants in terms of NRPE and GWP—different variants according to the type of parking: un. underground, in. individual garage, out. outside parking. In existing buildings, the underground parking is only accounted for at the E0 stage, i.e. the initial construction. E0 scenario only implements common practice variants. That is why both types of outside parking spaces—out.cp asphalt, out.bp concrete mono bloc paving—are presented

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Vertical elements present the largest impacts for the majority of new construction scenarios. For retrofitting, however, the elements bearing the largest share of responsibility differ according to indicators and construction typologies. Another interesting result is the trend of impact within one scenario and between scenarios (E0 to S3). Within one scenario, we can observe the influence of parking places in the overall impact for GWP: An underground (un.) parking presents the highest values and an outdoor parking place (out.cp) the lowest. For NRPE consumption, results are different. Individual garage (in.) presents lower impacts in multi-family houses, and outdoor parking (out.cp) is better in single-family houses, while underground (un.) have always the largest impact.

Between scenarios, results for renovation projects present an increment of impacts that vary from 300 to 350% for new constructions and 15 to 35% for single- and multi-family houses and for both indicators. This result shows the weight of materials in terms of environmental impact when building energy performance is improved. These observations underline the benefits of building retrofit: A higher energy performance allows reaching the intermediate targets even though the embodied impacts increase. Regarding new constructions, whatever the label (S1 to S3), the techniques of current practice do not allow reaching the targets.

For best practice (.bp) variants, the results presented in Fig. 10 are moderately improved. Environmental impacts of new buildings are on average minimized by 20% for NRPE and 25% for GWP. Although for retrofitting the conclusions are similar to those of current practice, the overall impacts are minimized with 9% for NRPE and 4% for GWP. Similar conclusions are also obtained for the largest contributors and trend of impacts within scenarios and between them. The advantage of best practice remains the achievement of targets for new constructions. New single-family houses complying with the Swiss regulation (SFH.n.S0) and all variants for new multi-family houses (MFH.n) reach the intermediate targets for both indicators.

Fig. 10
figure 10

Embodied impacts for best practice (bp) variants in terms of NRPE and GWP—different variants according to the type of parking: un. underground, in. individual garage, out. outside parking: concrete mono bloc paving

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Based on the observation of retrofitting projects and new constructions, we conclude on the possibility to reach easily the intermediate targets in the case of a renovation. Regarding new constructions, it is possible to reach the targets only by implementing best practices for multi-family houses and optimal insulation for single-family houses.

Mobility-related results

The divergent proportion of tenants and owners (Table 9) explains the variation of the results between single- and multi-family houses, which are 10 to 25% higher for single-family houses in central, suburban and peri-urban areas (Fig. 11). Global warming potential (GWP) results follow a similar trend as non-renewable primary energy (NRPE) results and are four to six times higher than the intermediate target, except in multi-family houses located in the centre which show the lower results. Those results emphasize the extent of the carbonation of current mobility as well as the demanding nature of the GWP target.

Fig. 11
figure 11

Results in terms of NRPE and GWP owing to current daily mobility induced by the building use, according to building type and territorial entity

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The highest results for single- and multi-family houses are those of the Peri-urban areas where the travelled distance is the longest among all the territorial entities. In terms of NRPE consumption, induced daily mobility of multi-family houses inhabitants is 44% higher in peri-urban areas than in the centre (55.6 kWh/m2 year), and for single-family houses, results (109.5 kWh/m2 year) rise by one third in comparison to results obtains in central areas (74.3 kWh/m2 year).

Considering the gap between the current mobility results and the intermediate targets, a projection is proposed assuming a potential future reduction of mobility-related impacts (Fig. 12) (SIA 2016a). Results are halved between both assessments. The methodology considers only technical improvements; changes assume neither a redistribution of dwelling owners nor a different recourse to conveyances. According to the results, technically improved mobility is not sufficient to meet the intermediate targets. Only one option complies with the goals. Results in peri-urban areas remain almost twice as high as the 30 kWh/m2 year target.

Fig. 12
figure 12

Results in terms of NRPE and GWP owing to a hypothetical reduced daily mobility induced by the building use, according to building type and territorial entity

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Scenario performances with reduced mobility-related impacts potential (GWP)

The improved mobility results are combined with the previous operational and embodied impacts in Figs. 13 and 14. These figures show future performances achievable according to the information and practices known and available today. Under those conditions, some variants meet the intermediate targets set for the 2050 horizon.

Fig. 13
figure 13

Reduced induced daily mobility, operational and embodied impacts in non-renewable primary energy consumption (NRPE)

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Fig. 14
figure 14

Global warming potential (GWP) for current induced daily mobility, operational and embodied impacts

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A general overlook of multi-family house results shows that all S1 to S3 scenarios (MFH.n/r.S1–S3) are below or close to achieving the target. The best-case corresponds to central MFH.r.S3.bp., with a NRPE consumption of 107.4 kWh/m2 year and a GWP of 10 kgCO2e/m2 year. Regarding retrofitted single-family houses, although the SFH.r.S3 scenarios are bordering the NRPE target, none of them meets the intermediate target of 120 kWh/m2 year. Nevertheless, some of the SFH.r.S1/S2/S3 scenarios in the centre and suburban areas reach the GWP goal. Due to the amount of CO2e embodied in the necessary material for the S3 scenarios, especially in the equipment (Figs. 9 and 10), SFH.n/r.S3 shows higher GWP than SFH.n/r.S1–S2.

SFH.n performs the worst among the assessed archetypes. None of the studied scenarios and variants meets the targets of both indicators. The best performing new single-family house shows results between 25 and 30% higher than NRPE targets and 40% above GWP goals.

Discussion

The detailed results presented as Appendix provide the data for the residential archetypes adapted to the Swiss context. In order to choose the archetypes, we looked for the most common representative features for each building type and each construction period. Although buildings are never identical (e.g. different climate conditions, orientations, shapes…), this method provides a reference framework and basic database useful to illustrate current issues related to the environmental impact weight of the built environment, and especially the residential sector.

The gap among single- and multi-family houses results underlines the influence of compactness and occupation on the energy performance of a building. In the framework of the 2000-W society, the intermediate targets for the built environment aim at an annual mean power per person of 840 W and 960 kgCO2e. Therefore, the occupation and the resulting living area per person affect the overall per capita performances of the dwellings. In this scope, the current issue of under-occupation of dwellings, which increases the living area per person, needs to be addressed in order to improve the environmental impacts of their inhabitants (Drouilles et al. 2017). In Switzerland, 75% of single-family houses have at least a living area of 100 m2 (FSO 2017a) and about half of the stock is occupied by one or two persons (Beyeler 2014).

This study highlights the overall environmental efficiency achieved within the current certification framework, given by the MINERGIE® labels and reference targets. The results show that only the most requiring scenario, S3 (energy positive buildings), is able to bring the performances close to the intermediate targets. Hence, in order to engage the built environment energy turn-around and meet the long-term targets set by the 2000-W society vision, the current certifications should be reconsidered to provide a framework about the whole building LCA. The current MINERGIE® labels mainly focus on operational final energy, and they should include requirements about embodied impacts and operational impacts owing to the induced daily mobility, which tend to weight up to 70% in the overall LCA of the most performing buildings. Using a different approach, Heeren et al. (2013) found similar results for a case study situated in Zurich, Switzerland.

The comparison of buildings of the 1940s–1970s in their current status (E0) with their retrofit scenario underlines the benefits of renovation projects. Thanks to low investment in material and construction, environmental impacts are generally far below the targets and limited to less than 15% of the overall results in the case of retrofitting projects. There is an immense improvement of energy performance and reduction of operational impacts: Operational impacts go from representing more than 80% of the NRPE consumption to 30% in the more performing scenarios, which also consume about three times less energy. Therefore, energy-wise and without taking into consideration density aspects, there should be no doubt about engaging a renovation process instead of a demolition/reconstruction one (Wastiels et al. 2016). Those results, however, raise some issues linked to the aspects of economic investment, timeline and technical feasibility of retrofit works (Jones et al. 2013; Fawcett 2014).

Another element identified with the study is the performance gap between the new construction of very low energy buildings (S2 scenarios) and energy positive buildings (S3 scenarios). Regarding the operational and embodied impacts of new buildings, the overall performance is similar (± 5 kWh/m2 year). These results raise the question of the benefit of achieving higher energy label when the added investment in material and construction erases the improvements made in reducing the operational impacts. This is observed for the new single-family house archetype, which obtains the same overall results for S2 and S3 scenarios despite an improvement of operational impacts. The results presented by this archetype remain at least more than 25% higher than the intermediate targets. In order to comply with the energy performance requirements to aspire to a MINERGIE-A® label certification, it would be still necessary to increase the insulation, the HVAC systems performance, the photovoltaic installation or the self-consumption potential using storage systems (Aguacil et al. 2017b); that is, to increase the amount of material and thus the overall embodied impacts. Therefore, despite a high environmental footprint owing to embodied impacts, a further step of this study would be to analyse the balance between drawbacks and benefits of photovoltaic installations in terms of operational energy savings and embodied impacts, in terms of renewable energy production, self-consumption and sharing by injection to the local network, and in terms of economic investments and long-term payback (Aguacil 2019).

The study underlines the central influence of operational impacts owing to the induced daily mobility within the overall buildings LCA. Considering the most performing scenarios, current mobility-related impacts represent about half the NRPE consumption and up to 80% of the GWP. The results show that vehicle technical improvement is not sufficient to meet the intermediate targets. Some studies have explored the conditions for operational impacts owing to the induced daily mobility to meet the targets (Scarinci et al. 2017), investigating the needed conveyance shift to be able to travel the same distance as today but meeting the intermediate targets. Through theoretical prospective scenarios, the preliminary study to this article states that operational impacts owing to the induced daily mobility will meet the targets only when low carbon individual motorized transport is used and when trips and transportation are optimized, i.e. when the scenario assumes technical improvements at the same time as an optimization of practices and individual behaviours (Drouilles et al. 2017).

More precisely, the results underline how location and building type influence the operational impacts owing to the induced daily mobility. In particular, the study confirms the weak performances associated with the induced daily mobility of single-family houses’ inhabitants living in peri-urban areas. These results raise the issue of an adaptation of the targets to the location or building type: Following their reduced induced daily mobility, people living in multi-family houses in central urban areas could afford to live in a less energy-performing dwelling. Another option could be the implementation of energy equalization between the urban centre and its periphery. It would allow peripheral inhabitants to have higher environmental impacts than inhabitants of the centre, where the immediate living environment and amenities make the reduction of the environmental footprint an easier task to achieve.

Conclusions

In this paper, we present the environmental impacts of 880 scenarios and variants by expanding the boundary of performance of buildings (construction and operation) and induced mobility. Four residential building archetypes, investigating renovation and new projects in the Swiss context, assume several energy-performance scenarios and variations of construction typologies, energy sources and heating, ventilation and air-conditioning (HVAC) and domestic hot water (DHW) systems, locations, private parking types and assessment horizons for induced daily mobility.

The main findings of the study concern the benefits of renovation projects, which bring the environmental impacts of the building construction and operation down to targets. Retrofit approaches are questionable regarding economic and feasibility aspects, but energy-wise, they tend to offer better performances than new buildings. Through the renovation of single- and multi-family houses to the highest energy performance, the indicators of non-renewable primary energy and global warming can be reduced respectively by 74% and 85%. For non-renewable primary energy, the retrofitting scenarios for both single- and multi-family houses present values that are 20% lower than those of new scenarios. Regarding global warming potential, results are 30% lower, for retrofitting scenarios than for new projects.

The results also confirm the expected weak performances of single-family houses in comparison to both multi-family houses and the intermediate targets. Environmental impacts of multi-family houses tend to be approximately 37% lower than those of single-family houses. They underline the positive effects of compactness for reducing environmental impacts due to building construction and operation. Those findings support the argument that in the scope of urban renewal projects, densification and energy efficiency actions must be coupled to comply with the 2000-W society framework and achieve reduced per capita environmental footprints.

Results highlight the influence of each aspect in the whole life-cycle assessment of the four analysed archetypes. Consequently, it underlines the benefit of conducting interdisciplinary approaches considering different assessment scales—from the architectural object to the integration at the urban and territorial level—to achieve a higher degree of sustainability. In perspective of this research, for increasing the robustness of conclusions, further uncertainty analyses are necessary by assessing the uncertainty in environmental impacts of buildings that derives from uncertainty in inputs.

The major output of this study relies on the implementation of a bottom-up methodology that provides reference values for the assessment of non-renewable energy and global warming potential indicators in the built environment in Switzerland. Based on the modelling and assessment of four building archetypes, the study provides 880 variants that can be combined for implementing an assessment on a larger scale. This database represents a consistent framework for professionals to make informed decisions by simultaneously considering the environmental impacts of building and the influence of location and territorial context. It especially offers the possibility (1) to run some preliminary environmental assessments from an isolated building to a group of residential buildings, e.g. a neighbourhood; (2) to arbitrate pros and cons, in terms of environmental impacts, of a retrofit or new construction project; (3) to provide a decision support on the type of action to engage depending on the location and archetype; (4) to revise the regulation in use from the perspective of its impact on current practice; (5) to assess current performance of buildings targeting high-energy efficiency certifications (e.g. MINERGIE® labels) or current regulation (e.g. SIA) in comparison with the intermediate targets for 2050; and (6) to consider the extent of the improvements needed regarding the environmental impacts owing to the induced daily mobility (IDM). The results support the fact that practitioners need to be aware of the current performances achievable in the built environment and of the remaining challenges to meet the targets for 2050, which are still intermediate goals towards the achievement of the 2000-W society by 2100.