Introduction

In the European Union, the overall building stock is responsible for about 40% of the total consumption of primary energy. Housing, in turn, accounts for the bulk of the energy consumption in this domain (Itard et al. 2008). Though there is significant potential for realising cost-effective energy savings and reductions in CO2 emissions in both new and existing buildings (McKinsey and Company 2009; Ürge-Vorsatz et al. 2007)—which would benefit society at large—certain market, technological and end-user characteristics are inhibiting rational, energy-saving choices in purchase and use (Koeppel and Ürge-Vorsatz 2007). This implies that marketing strategies and policies aimed at overcoming the barriers that are inhibiting the application of energy-efficient technologies and conceptsFootnote 1 are crucially important in the efforts to lower greenhouse gas emissions from buildings.

More governments and companies are realising the energy-saving potential of dwellings and are pursuing the required strategies and policies. Researchers and networks have proposed different building codes and definitions to significantly reduce the energy consumed by housing. The first energy efficiency codes for dwellings were set in the 1970s in response to the oil crisis (Deringer et al. 2004). Since then, the range has expanded considerably, from regulatory and voluntary instruments in the initial phase to financial incentives and economic instruments (IEA 2005). These instruments regularly introduce definitions for highly energy-efficient housing concepts. ‘Passive house’,Footnote 2 for example, has recently been successfully defined and introduced in different countries and policies (Elswijk and Kaan 2008; Mlecnik et al. 2010).

One of the mandatory actions for buildings in the EU Action Plan on Energy Efficiency [COM(2006)545] prompted the Commission to devise a strategy for the uptake of a definition of so-called ‘nearly zero’ energy buildings with a view to a more widespread deployment of such buildings by 2020.Footnote 3 The European Commission now expects Member States to introduce and register ‘nearly zero-energy’ buildingsFootnote 4: This is requested in the recast of the Directive of the European Parliament and of the Council on the energy performance of buildings (EPBD 2010). The European Parliament (2009) recommended a focus on buildings with CO2 emissions and primary energy consumption which are low or equal to zero. National, regional or local tax incentives, financial instruments and lower rates of VAT (European Parliament 2009: Amendment 102) are expected to support the diffusion. Despite the numerous actions towards zero emission buildings and the excitement of the term ‘zero’, major challenges need to be met in the development of such regional definitions, in particular in relation to the lack of common understanding (Marszal et al. 2010). Defining nearly zero-energy buildings requires a prescriptive approach with stricter implementation of more ambitious strategies and targets and more policy commitment to market change (Atanasiu 2010). Member States can provide more clarity by defining their expectations in, for example, their building codes and tax legislation.

Meantime, the media coverage and the political attention paid to climate change and to lowering the primary energy demand appear to have sent the housing industry into a kind of ‘carbon wild west’. Promoters, developers and communities bandy around words like ‘passive’ houses, ‘climate neutral’ living, ‘carbon-neutral’ streets and ‘zero-energy’ developments, sometimes without clear definitions, target values or (policy) evaluation procedures. Hence, one major obstacle for the implementation of the implementation of the recast of the energy performance of buildings Directive (EPBD 2010) seems to be the linguistic, cross-regional and legislative confusion caused by the number and variety of definitions and their historically determined meaning.

Outline of research

Research goal

To speed up the diffusion of the use of highly energy-efficient housing, it is necessary that policy provides visible and widely accepted definitions that help companies and other actors to distinguish themselves from the competition. It therefore makes sense to map out an overview of existing marketing and legal definitions for highly energy-efficient housing concepts, particularly with a view to policy adoption. The goal of this research is to identify openings and barriers for the adoption of existing definitions for highly energy-efficient housing concepts in Belgian and Dutch policy, which can also serve as an example for other European countries.

Research question

The main research question was: What definitions can be expected to be adopted for nearly zero-energy housing in Belgium and the Netherlands? This question was explored by asking the following subquestions:

  1. 1.

    What terms have been adopted in relation to highly energy-efficient housing concepts, especially in Belgium and the Netherlands, and by whom?

  2. 2.

    What definitions have been introduced in other countries?

  3. 3.

    What definitions show favourable innovation characteristics for further diffusion in Belgium and the Netherlands?

Research methodology

Diffusion of innovation can be driven by communication within a society, which increases the attractiveness of an innovation (Rogers 2003). In this perspective, it is relevant to frame the study within the innovation diffusion context, i.e. the communication of highly energy-efficient housing concepts.

Based on innovation diffusion theory (Rogers 2003), the study defined both open and closed questions to examine perceived attributes of existing highly energy-efficient housing concepts. How a relevant interview method can be derived from diffusion theory has been discussed in (Mlecnik et al. 2010). General questions in the interview used in this paper requested information about the existence of nearly zero-energy housing, their market penetration and national and legal recognition, including financial benefits, regional references, education and communication efforts and expert appreciation. Demonstrability questions were developed to document the degree to which nearly zero energy may be experimented with and is recognised by the state or region for incorporation in existing developments. Visibility questions asked about the degree to which low energy, passive house and nearly zero energy is visible to others. Further, compatibility was regarded as the degree to which nearly zero-energy definitions are consistent with the (recast of the) EPBD (2010).

After trial and regrouping, a final questionnaire contained three main groups of questions that addressed the relative advantage, complexity, demonstrability and visibility of highly energy-efficient housing as well as their compatibility with building code development:

  1. 1.

    Questions about low-carbon, low-energy, zero-energy or passive house development in Member States or region (directed at commercial actors and networks, change agents and knowledge institutes)

  2. 2.

    Questions about the compatibility of low-energy housing development with the development of building code (for experts only)

  3. 3.

    Questions about the latest development of relevant labels (for label developers only)

To reply to the questionnaire, experts from different countries were identified and addressed. Amongst other, a list of experts was provided by the European Council for an Energy Efficient Economy. Additionally, leading experts from national and regional passive house organisations and known label developers were consulted.

“Adoption of definitions for highly energy-efficient housing in Belgium and the Netherlands” section addresses the first question by combining research results with literature study on the emergence of highly energy-efficient housing concepts in Belgium and the Netherlands. The findings were reflected with interviews with regional key stakeholders (academic stakeholders, energy efficiency experts) and during discussions in working groups (working group ‘close the circle—energy’ of the Flemish transition arena sustainable living and construction: Duwobo 2010). Using the collected data, the adopted definitions were classified in five categories: general terms used, relevant definitions in research, definitions from demonstration projects, definitions introduced for market creation and legal definitions.

“Experiences in other countries” section deals with question 2 by examining interviewees’ responses regarding existing legal definitions in the light of attaining the European goal of nearly zero-energy housing with a focus (detected from the research results) on zero-carbon and zero-energy definitions. It analyses the recent working definitions to trace if they can be translated into attainable criteria over time in the Netherlands and Belgium.

In “Definitions with favourable innovation characteristics” section, the diffusion characteristics related to several working definitions are discussed using the theory of innovation diffusion, and question 3 is answered by analysing the research results in terms of the possible adoption of definitions. This analysis unveils barriers that could potentially obstruct the adoption of some definitions and identifies cross-country opportunities for removing them.

Limitations of the research

This questionnaire was addressed to 188 Member State professionals involved in the development of labels for low-carbon, low-energy, zero-energy or passive houses. In total, 25 completed replies were received from 15 different countries. The limitations of the small interview sample need to be recognised.

Although the professionals were carefully selected, answers were diverse and reflected the expert’s own experience and their view on the state of adoption of highly energy-efficient houses in the country. Some experts or regional representatives showed only limited experience with nearly zero-energy houses or even none.

This research method led to replies, detailed comments, additional references and empirical data from a small sample, but with a good international distribution. Possible knowledge gaps were tackled with further literature search and discussions with leading experts.

Since building traditions and practices can vary according to climate and country, the research focussed on western Europe, and Belgium and the Netherlands in particular. It addresses definitions used in countries that are dominated in particular by a heating demand and new housing. It does not specifically address definitions for energy-efficient or energy-positive non-residential buildings, nor districts or communities.

Experience in Belgium can be dissimilar from experience in the Netherlands, but differences in the adoption of highly energy-efficient housing concepts can generate added value when the findings are compared, also with other countries.

Adoption of definitions for highly energy-efficient housing in Belgium and the Netherlands

General terms used

Historically, energy efficiency has always figured as a theme in regional research and engineering, but most of the time it was confined to conversion processes involving large energy flows (Lysen 1996). Whereas the energy crises of the 1970s rekindled the interest in the field of energy-efficient housing, no statutory low-energy standards for new dwellings were implemented in Belgium and the Netherlands, like in, for example, Sweden and Denmark. This led to various general terms introduced in daily language for communication purposes.

In Belgium and the Netherlands, ‘low-energy’ buildings are usually defined as buildings, which have been designed with the explicit intention of using less energy than standard buildings. Sometimes specific energy requirements are set out by energy consultants, which then lead to performance-based strategies. For example, in the Netherlands and Belgium, the regional implementations of the European Energy Performance of Building Directive (EPBD 2002) have occasionally been used for project targets (e.g. an ‘E-level’ of 40 or 60 in Flanders and an ‘EPC’ of 0.4 or 0.6 in the Netherlands), but potential problems have also been reported on building controls and performance guarantees (Visscher et al. 2010).

Whilst in Belgium the term ‘passive house’ has seen a broad market introduction (Mlecnik 2008), in the Netherlands, the terms ‘climate’ or ‘CO2 neutral’, or ‘zero energy’ are often used (PEGO 2009). ‘Zero carbon’ and ‘carbon neutral’ are used terms in Dutch marketing, but they can be understood in various ways, with no official definition. In the Netherlands, several authors have proposed local definitions for further use: CO2-neutral homes or CO2-emission-free houses (e.g. Van Hal 2007), zero-energy or energy-neutral houses (e.g. Rovers and Rovers 2008) or passive houses (e.g. Mlecnik 2009). CO2 neutral is also applied for larger territories within communities (e.g. Roos and Straathof 2008).

The concept of ‘zero-energy’ is also subject to different interpretations and frequently occurs in Dutch and Belgian marketing jargon. ‘Zero-energy’ is generally interpreted as ‘net zero energy’, i.e. equilibrium between the used and produced energy.

Relevant definitions in research

Since the 1970s, different research models were proposed in different regions. In the Belgian Walloon region, the Passive and Low Energy Architecture movement (Cook 2002) received considerable interest, and terms such as ‘passive solar architecture’ emerged as the expression of a design philosophy for low-energy buildings that takes account of the natural environment. In architecture, the term ‘climate-sympathetic architecture’ subsequently appeared with regard to buildings which, because they are designed along the lines of ‘passive solar’ criteria, use the building envelope as the primary climate control and make mechanical installations supplementary. The term ‘bioclimatic (or sustainable) architecture’ was widely disseminated in the Walloon Region and refers to an alternative way of constructing buildings which takes account of local climatic conditions and which harnesses various passive solar technologies to improve energy efficiency; the term ‘passive solar technologies’ refers to heating or cooling technology that passively absorbs (or protects from, e.g. natural shading) the energy of the sun and has no moving components (Tzikopoulos et al. 2005). In view of its potential for generating significant energy savings and reducing greenhouse gas emissions (Tzikopoulos et al. 2005), bioclimatic architecture has continued to receive a fair amount of attention worldwide in recent years (e.g. Radovic 1996; Gallo et al. 1997; Zain-Ahmed et al. 2002; Nahar et al. 2003) and is regarded as an important parameter in contemporary architecture (Donald 1998), especially in Belgium (see, for example, UCL 2010).

Alternatively, the term ‘integrated (energy) design’ (IED) was more often mentioned in the Flemish Region, especially by energy consultants, which usually refers to a design process that is meant to lower the operational costs of the building, whilst striving for a comfortable indoor climate and lower emissions (see also: Syneffa 2008). In the Netherlands, Lysen (1996) initiated the ‘Trias Energica’—now commonly coined the ‘Trias Energetica’ (VROM 2010)—as a research model to frame the merits of putting energy efficiency before using renewable energy. The Trias Energetica now represents an academically acknowledged three-step priority strategy: (1) reduce the demand, (2) use renewable energy sources and (3) solve the residual demand efficiently and cleanly. It is used in official communication, also for highly energy-efficient housing and construction (for example, VROM 2010).

International knowledge exchange had an impact on the further development of integrated concepts in all regions. For example, the work of experts from the International Energy Agency (IEA), within the Solar Heating Cooling (SHC) Programme, led to national guidelines in Belgium and the Netherlands on how to design, construct and evaluate cost-effective, energy-efficient ‘passive’ solar homes. The currently used research framework of the ‘passive house’ concept was developed in 1988 by Bo Adamson at the University of Lund, Sweden, from the basic IED strategy for lowering energy consumption by, for example, reducing transmission, ventilation and infiltration losses and optimising solar gains (Feist and Adamson 1989). ‘Passive houses’ were first defined as buildings which, in the central European climate, have a negligible heating energy requirement and therefore need no active heating.Footnote 5 Direct and indirect European funding (for example, PEP 2008) enabled the passive house concept also to be introduced to expertsFootnote 6 and policymakers in Belgium and the Netherlands. The project-based stop-and-go efforts for the dissemination of the passive house concept have led to regional differences in the diffusion of the passive house concept (Elswijk and Kaan 2008; Mlecnik et al. 2010).

Belgian and Dutch researchers developed national guidelines on how to design, construct and evaluate such energy-efficient passive houses in the regional context. Researchers applied realistic technical solutions to translate some of the more general bioclimatic design criteria into specific recommendations for target values compatible with the local climate.Footnote 7

Meantime, ‘cradle-to-cradle’Footnote 8 and ‘sustainable’ or ‘green’Footnote 9 houses are attracting some interest in both the Netherlands and Belgium. As a whole, buildings are much more complex than materials or products alone, but this complexity enables them to close energy, water and material cycles through interconnected loops (van den Dobbelsteen 2008). Experience of buildings in this domain still has to be gained in projects, but it could breathe new life into a Trias Ecologica approach to sustainable building (van den Dobbelsteen 2008).

Definitions from demonstration projects

The late 1970s saw the emergence of rudimentary ideas for integrated concepts and experimental minimum-energy dwellings (see Table 1 for some experiences in Belgium and the Netherlands). As in many countries, several terms have been used by individual architects and companies in Belgium and the Netherlands by naming experiments and framing demonstration projects. Examples are the ‘minimum-energy house’ (Kristinsson 2007), ‘energy-balance home’ (Remu 2000), ‘energy house’ (Kristinsson 1999) and ‘green house’ (Groenwoning 2010).

Table 1 Introduction of energy design concepts in experiments in the 1980s: example in the Netherlands (Kristinsson 2007) and in Belgium (Wouters et al. 1986; Vlaams Parlement 1998)
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Since these definitions were developed in only a few demonstration projects, until now these definitions did not find a strong enough response in the mainstream construction industry. However, some of these terms—and related positive and negative (!) experiences: see Table 1—still remain in the collective memory of interviewed experts.

In literature terms like ‘EQuilibrium™ house’ (CMHC 2010), ‘active house’ (Marszal et al. 2010), ‘plus-energy house’ (Activehouse 2010) and ‘plushaus’ (Wappler 2000) can also be found, but these terms have not been reported in interviews from Belgium and the Netherlands.

Definitions introduced for market creation

Due to the lack of policy definition for highly energy-efficient houses, different definitions were introduced by business networks and mixed business/policy networks. In the Netherlands, a general policy-related definition for highly energy-efficient houses is missing.Footnote 10 In the Belgian Walloon Region, low-energy houses were defined with more specific criteria by the regional government within the framework of a clustering initiative (CALE 2010). In the Brussels Capital Region, energy performance ambition levels were defined in a demonstration programme with associated grants (Leefmilieu Brussel 2010). The Flemish assembly of environmental non-profit organisations (BBLV 2010) introduced a charter for defining low-energy houses according to a German model and kilowatt-hour per square metre definition,Footnote 11 but it was not accepted in policy initiatives. Flemish architects recently received the proposal to become listed when working on low-energy houses (EA 2010). In parallel, business networks aiming for a higher ambition level introduced a passive house definition and labelling in the Flemish Region, the Brussels Capital Region, the Walloon Region and the Netherlands (PEP 2008; Mlecnik et al. 2010). Table 2 summarises the definitions introduced for market creation in Belgium and the Netherlands.

Table 2 Definitions from business networking initiatives in Belgium and the Netherlands
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Legal definitions

Next to the previous definitions listed in Table 2, in Belgium definitions for the low-energy house, the passive house and the zero-energy house have recently been formalised in federal income taxFootnote 12 legislation (Belgisch Staatsblad—Moniteur Belge 2009, 2010) as shown in Table 3. A recent Royal Decree (Belgisch Staatsblad—Moniteur Belge 2010) reconfirms these definitions for 2011–2012 and defines that the ‘renewable energy’ in the ‘zero-energy’ house should be produced by:

  1. 1.

    A system of water heating using solar energy

  2. 2.

    Solar panels for the conversion of solar energy into electrical energy

  3. 3.

    Heat pumps that use energy stored in the form of heat:

    • In the surrounding air

    • Under the soil surface

    • In surface water

Table 3 Definitions of highly energy-efficient houses in Belgium (Belgisch Staatsblad—Moniteur Belge 2009)
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The number of kilowatt-hours generated renewable energy has to be calculated with the regional EPBD method provided by the Directive CE/2006/32 applicable on the house. An exception is made when this method does not provide an evaluation of the production of renewable energy. In that case, the conversion efficiency and the ratio between input and output of the systems and equipment for renewable energy have to be valued by means of a European/international procedure.

In the Netherlands, no definitions have been adopted so far in legal references. The Dutch agency for innovation and sustainability policy (Agentschap.nl) has tried to steer the definition process with a report (PEGO 2009) but without explicitly defining nearly zero-energy houses. Dutch experts argue if energy demand only needs to be lowered on the scale of a house, since energy can also be produced at a higher level such as the site, district or community (Ravesloot 2005). The term ‘energy neutral’ is being addressed in the Netherlands by a construction norm, defining the energy performance on location calculation method, which is applied to developments larger than 300 living units and by attributing a maximum score to energy-neutral neighbourhoods (Verlinden et al. 1999). Recently, a Dutch report (DHV 2010) also concluded that the term ‘climate neutral’ should no longer be used for utility buildings: The term ‘energy neutral’ is recommended when addressing buildings and ‘CO2 neutral’ when addressing the organisational context.

Discussion: the policy challenge of introducing ‘nearly zero energy’ in Belgium and the Netherlands

The previous research data show that many definitions are already used. Definitions used in individual marketing efforts or demonstration projects are probably not widely diffused. Several experts stated that the knowledge of building experts, the collaborative interests of consultant engineers and research scientists and the lessons of nature and of indigenous architecture should not be ignored in housing. Researchers apparently developed their own research language throughout the years. The ‘passive house’, born from the research field and adopted by industry, can currently be considered as a state-of-the-art culmination of many of the research efforts in bioclimatic architecture and integrated energy design, whilst using the Trias Energetica.

The Belgian Regions and the Netherlands are (thinking about) tightening the energy performance levels (and the current implementation of the EPBD) towards ‘low energy’ or ‘nearly zero energy’, but definitions and level of implementation can vary in different regions. Tables 2 and 3 show that definitions vary, even for the passive house, and that earlier market definitions can conflict with legal definitions. Some interviewees mentioned that efforts in harmonization are wished for. The findings are in line with the study of Thomsen et al. (2008) for 22 European countries: In some countries, official definitions co-exist with unofficial definitions.

Compared to the Netherlands, in Belgium, the legal definition supports the ‘passive house’ as a political ambition to lower energy consumption in the building sector—see also Dyrbol et al. (2008) and Mlecnik et al. (2010) for a European comparison—and as a preferred model for business development—this model is also supported by EeB (2009). This has historical reasons: The introduction of previous grants and tax relief for passive houses in Belgium helped to create a niche market for similar demonstration projects (Mlecnik and Marrecau 2008; Mlecnik 2008). This niche market is currently supported by business networks, research centres and a few policy makers. ‘Passive house’ does not conflict with commonly regionally used research definitions, although researchers prefer to look beyond the energy scope or beyond the building.

The European Parliament recommended to introduce financial incentives and to express the energy performance of a building in a transparent manner and to include a numeric indicator of primary energy use expressed in kilowatt-hour per square metre per year (European Parliament 2009; Amendment 82). Table 4 lists how several definition initiatives are currently related to financial incentives and whether tools are recommended for an expression in kilowatt-hour per square metre per year. Table 4 shows that the relative advantage (financial incentives) and/or interregional compatibility with the EPBD recast (tool for calculation of primary energy use) of highly energy-efficient housing definitions can be improved.

Table 4 Possible barriers (relative advantage and compatibility) of definitions of highly energy-efficient houses in Belgium and in the Netherlands, in the framework of the EPBD recast
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The research further notes that the ‘integrated energy design’ and the ‘cradle-to-cradle’ discussion were also incorporated in the transition arena on sustainable housing in Belgium. This led, amongst others, to a recommendation to stimulate the further development of energy-neutral housing and to facilitate a positive market climate for passive houses (Dries 2007). When the definitions are reflected in relation to their historical background, e.g. the definition of criteria for bioclimatic architecture (Wouters et al. 1993), it is noted that in the case of ‘zero-energy’ and ‘passive house’, there are currently no legal specifications for good indoor climate conditions and an attractive design for a majority of potential clients. Since the recast of the EPBD (2010) offers opportunities to revise definitions, the next section puts a focus on comparing experiences with other countries.

Experiences in other countries

UK

A ‘true’ zero-carbon homeFootnote 13 is expected to emit no CO2 and does not need to import grid electricity (RAB 2007). Heating loads are minimal and any remaining heating needs are met with renewable fuels and technologies. Similarly, electricity demand is reduced to a minimum and any remaining demand is met with renewable electricity. In reality, the achievement of ‘true zero carbon’ is a costly business as energy needs to be stored in order to overcome the mismatch between supply and demand in many renewable systems (RAB 2007). The alternative is the ‘net-zero-carbon’ home, which emits no net CO2 on an annual basis, but could be either emitting or offsetting it at any given moment.

The term ‘zero-carbon’ homes appeared in official UK policy even though the technical aspects still had to be defined. The UK government has pledged to achieve zero-carbon standards for all new government-funded homes by 2016 (Jones et al. 2008). In February 2007, the Welsh Assembly announced that all new buildings funded by the Assembly must achieve zero carbon by 2011, but it was reported that it was still to provide a definition of zero carbon and explain how the targets are to be achieved (Jones et al. 2008).

In 2007, England adopted the BRE Code for Sustainable Homes (BRE 2006) as a reference framework. The government introduced the Code for Sustainable Homes (CSH) rating as a first major attempt to define ‘sustainability in the built environment’. The CSH rates the sustainability of a development on the basis of nine key criteria, only one of which is energy and CO2 emissions (Saunderson et al. 2008). This initial step also included a first definition of a zero-carbon home.

The latest version of the CLG guide (CLG 2009:46) defines a home as zero carbon when ‘net CO2 emissions resulting from ALL energy used in the dwelling are zero or better. This includes the energy consumed in the operation of the space heating/cooling and hot-water systems, ventilation, all internal lighting, cooking and all electrical appliances.’

Dwellings must meet the minimum mandatory energy requirements for CSH Level 5—which means that that emissions must be zero or better. The definition (CLG 2009:46) further states that “A ‘zero-carbon home’ is also required to have a Heat Loss Parameter (covering walls, windows, air-tightness and other building-design issues) of 0.8 W/m2 K or less, and net zero CO2 emissions from the use of appliances and cooking in the home (i.e. on average over a year).” According to the UK definition, off-site renewables can only be used if they are directly supplied to the dwellings by private wire.

Further, a zero-carbon house is also defined in the Stamp Duty Land Tax SDLT (UK Government 2007) as a house that should meet the following criteria: fabric energy efficiency (minimum HLP of 0.8 W/m2 K), space heating demand (up to 15 kWh/m2/year) and carbon neutral over a year. SDLT and CSH version 2 definitions of zero carbon are similar, except for the unregulated energyFootnote 14 that is a fixed value for the SDLT (Poveda 2010).

‘Zero-energy’ definitions

The term ‘net zero energy’ first appeared in US law, but it was defined for commercial buildings. On 19 December 2007, the US Administration passed the Energy Security and Independence Act outlining plans for ‘net-zero-energy commercial buildings’ and stating that all new commercial buildings should attain net-zero-energy status by 2030 (USC 2007). In Section 422 (a) (3) (USC 2007:113), ‘zero-net-energy commercial building’ is defined as a high-performance commercial building that is designed, constructed and operated in such as way that:

  • It has a much-reduced energy requirement.

  • It meets the residual energy needs from sources that do not produce greenhouse gases.

  • It produces no net emissions of greenhouse gases.

  • It is economically viable.

In a number of publications (Torcellini and Crawley 2006; Laustsen 2008b; Crawley et al. 2009; Marszal and Heiselberg 2009), authors present the wide variety of zero-energy working definitions and highlight the significance of these definitions in the framework of final design and actual performance. Torcellini et al. (2006) have defined ‘net zero site energy’ and ‘net zero source energy’.Footnote 15 ‘Net zero site energy’ means that a site produces at least the same amount energy that it uses in a year, regardless of energy type. ‘Net zero source energy’ refers to a system whereby imported and exported energy is multiplied by a primary energy converter, which allows for some degree of flexibility in the use of heating fuels. Hernandez and Kenny (2010) attempted to introduce a further element in the definition of zero-energy buildings, viz. the embodied energyFootnote 16 of the materials used for the construction of the building and its systems. ‘Energy-positive’ buildings are defined as buildings that are able to produce more energy than they use.

Discussions are still underway at international level (IEA SHC Task 40 2010) to determine whether these definitions should be evaluated on an annual or on a seasonal basis to reduce the energy mismatch. The ‘Source’ definition is difficult to interpret since there is no readily available data on the location, source and conversion (Torcellini and Crawley 2006). ‘Site’ can also be difficult to define, e.g. does it refer to the building site or the total ground surface? Building owners are primarily interested in obtaining verification that their building has ‘net-zero-energy-cost’ status, but this is difficult to determine in practice because of the non-transparent structure of energy rates (Torcellini and Crawley 2006). Sartori et al. (2010) developed a series of criteria that need to be evaluated in order to achieve a sound zero-energy definition.

There are many unanswered questions. For instance, there is no standardised way of making zero-energy calculations (Voss 2008; PEGO 2009). The problem is not so much the lack of a definition but rather the need for appropriate analysis and representation methodologies to reveal differences and commonalities (Voss 2008). As evaluations of zero-energy projects are usually based on calculations, decisions need to be taken on which units to use (final energy, primary energy, non-renewable share of primary energy, CO2, CO2 equivalent etc.) (Voss 2008; PEGO 2009).

Discussion: relevance for Belgium and the Netherlands

The research detected only a few additional legal references considering the definition of zero-energy or zero-carbon buildings (see Table 5 for an overview). The starting point for all common definitions is a far lower level of energy consumption than standard. ‘Zero carbon’ or ‘net zero energy’ has not been defined in official Belgian or Dutch policy although the above-mentioned discussions have been acknowledged by the Dutch policy body responsible for the energy transition (PEGO 2009). Belgium opted for another legal approach to the ‘zero-energy’ house (see Tables 2 and 5).

Table 5 Legal references and key requirements for ‘nearly zero-energy’ buildings (status December 2009)
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The implementation of the UK ‘zero-carbon’ definition can be considered as a regional implementation. Regarding the specificity of the Belgian and Dutch context, it could inspire in particular the Netherlands, where the term ‘carbon neutral’ is often used in marketing. However, the use of an assessment method for zero-carbon homes, such as the Code for Sustainable Homes with its emphasis on point scoring, may cause people to see higher complexity and sustainability as add-ons, rather than integral elements in housing design (Jones et al. 2008). Also, many players in UK industry expressed concern at the inclusion of the private wire connection (Saunderson et al. 2008).

Terms like ‘zero carbon’ and ‘zero net energy’ were coined to simplify the issue and make it more ‘accessible’, but these simplifications may themselves be to blame for constraining debate and stifling innovation (Saunderson et al. 2008). It can therefore be questioned whether introducing such new definitions, next to the already existing research, marketing and legal definitions in Belgium and the Netherlands, will improve innovation diffusion.

Definitions with favourable innovation characteristics

Relating definitions to innovation diffusion

The goal in the Netherlands and Belgium is to increase the adoption of highly energy-efficient housing (PEGO 2009; Dries 2007). Within this framework, ‘zero-energy’ or ‘zero-carbon’ housing can be considered an innovation for Belgium and the Netherlands, in addition to the ‘passive house’. Clear definitions of highly energy-efficient housing concepts geared to attaining ‘nearly zero-energy’ homes are expected to bring this goal closer and promote innovation in housing.

In this paper, definitions of such innovations are seen as a communication tool in a changing economic and legal landscape. Innovation diffusion theory examines the processes whereby an innovation is communicated through certain channels over time amongst the members of a social system (Rogers 2003). Mobilising resources and creating legitimacy are two basic functions that innovation systems need in order to develop (Alkemade and Hekkert 2009). Clear definitions can create legitimacy and associated resources can form a basis for the development of market infrastructure.

Rogers (2003) identifies five perceived attributes of an innovation that can help to explain the rate of adoption of an innovation: relative advantage, complexity, trialability (in this paper ‘demonstrability’ is used), observability (here ‘visibility’ is used) and compatibility. Table 6 gives examples how these attributes can be interpreted for our previous discussion.

Table 6 Examples of how definitions used can have an impact on the adoption of highly energy-efficient housing concepts, using Rogers’ innovation diffusion characteristics (2003)
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Opportunities and barriers in the Netherlands

The energy transition platform for the built environment has put forward several definitions for use and evaluation in the Dutch market and wanted to define further requirements for energy-neutral and CO2-neutral building projects relating to, for example, maximum energy use per square metre (PEGO 2009:43). Therefore a ‘carbon-neutral’ approach appears to be most compatible with the current market and policy situation. However, it should be noted that, when the term ‘zero carbon’ was first introduced in the UK and prototypes were developed, case studies within this framework showed that an integrated energy design can offer a total package of both passive and active measures to achieve zero carbon (Jones et al. 2008). In this perspective, defining more precisely the integrated energy design and the Trias Energetica approach can also result in zero carbon solutions for the Netherlands. Regarding the market support, this might also result in ‘passive house’ as a preferred term. A strategy for formulating any definition is still needed, as well as appropriate calculation tools and a study to determine compatibility with the new regulations on the energy performance of buildings.

The market appeal of terms for highly energy-efficient housing in the Netherlands is currently limited because no definitions have been adopted so far in legal references. However, demonstrability is high and the Dutch agency for innovation and sustainability policy (Agentschap.nl) has tried to steer the definition process and acknowledged the complexity of the transition process. Many definitions are currently in circulation, not least in the application files of the subsidy programme for demonstration projects (in Dutch: ‘Unieke Kansen Regeling’ or ‘UKR’).

At present, a definition of ‘low energy’ based on the Dutch energy performance legislation has the highest visibility in official websites, whilst ‘zero carbon’ is often used in projects. Both might have low compatibility with the desire of the European Parliament to express indicators of primary energy use in kilowatt-hour per square metre per year (see Table 4). In the meantime, ‘passive house’ is used by industry networks and a few communities and housing associations.

At present, no specific relative advantage has been attributed to certain definitions—for example, in the form of grants or tax benefits, or social prestige for the market players. This might lead to low visibility and market confusion. The Dutch ‘Unieke Kansen Regeling’ programme allows communities to apply for grants for demonstration projects for very-low-energy houses. A continuation of this programme potentially offers a trial of grants for certain (prescribed) definitions. Experiences from the previous call for projects can lead to defining favourable definitions for a next call. Also, other countries, like Belgium, might provide experiences from a more advanced policy situation.

Opportunities and barriers in Belgium

In Belgium, definitions for the low-energy house, the passive house and the zero-energy house have been formalised in tax legislation (Belgisch Staatsblad—Moniteur Belge 2009, 2010), which creates attractiveness to use these definitions and gives an opportunity to reduce complexity. The tax law provides a clear framework plus income tax relief incentives which enhance the market appeal by creating a clear relative advantage. The current tax benefits based on energy performance will make people perceive a higher energy performance as superior to other alternatives possibly leading to a faster rate of adoption.

The introduction of the low-energy and zero-energy category, in addition to the already existing passive house category, has been perceived as allowing demonstrability consistent with the existing regional value of the ‘passive house’.Footnote 17 It would therefore be reasonable to expect that past experience and the needs of (potential) adopters will be more readily adopted.

In this context, the visibility of uniform definitions to potential adopters can be considered a key factor in diffusion. This visibility is built up by, amongst others, business networks, mixed policy/business networks and promotion by the federal government taxation services (for example, at building fairs).

However, the tax law and market definitions are currently not compatible with the regional EPBD (2002) implementation. The diffusion of these definitions might therefore be hindered by current regional initiatives promoting other or previous EPBD-related definitions. For example, Table 7 shows the additional grants available under the energy performance regulations in the Flemish Region and in the Brussels Capital Region.

Table 7 Grants for new low-energy housing categories in the Flemish Region, according to E-level (building energy performance level) for building applications from 1 January 2010 (VEA 2010) and in the Brussels Capital Region (Leefmilieu Brussel 2010)
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The Brussels Capital Region offers a specific situation. The Flemish Region and the Brussels Capital Region are pursuing the same strategy to increase the relative advantage for a better energy performance by buildings. In the Brussels Capital Region—in contrast with the Flemish Region—the definitions of the passive house are maintained for grants, regardless of the legislation on the energy performance of buildings. This is largely due to the good visibility and compatibility that the definition provides within the framework of the policy programme for demonstration buildings in the Brussels Capital Region. Moreover, the calculation tools for passive houses must be used for evaluation, which is compatible with the design practice of passive houses. In the Brussels Capital Region, the passive house is the only category to be rewarded with grants for new houses. ‘Very low energy’ (≤30 kWh/m2/year) and ‘low energy’ also receive grants, but only for renovation.

EPBD incompatibilities should be solved when introducing the EPBD recast (EPBD 2010). Previous research has shown that the current energy performance standard can lead to ‘lock-in’ effects by encouraging only incremental innovation and techniques that reflect the principles in the energy performance policy (Beerepoot 2007:204). It is recommended to avoid penalising techniques that break with convention and that are needed for the transition to nearly zero-energy housing, e.g. some experts noted that ‘passive houses’ are systematically penalised for fictitious overheating in Flemish EPBD implementation.Footnote 18

Discussion

Table 8 presents a summarised interpretation of the discussion to show how definitions can influence the rate of adoption for nearly zero-energy housing in three regions. Table 8 shows that the policy interpretation of ‘nearly zero-energy’ into workable local definitions might differ from region to region, depending on the adoption history of highly energy-efficient housing concepts and the existence of specific policy programmes which have already introduced certain definitions. Where necessary, the relative advantage, demonstrability, visibility and compatibility of favoured definitions can be enhanced by energy policy initiatives to increase the rate of adoption.

Table 8 Innovation characteristics that can influence the rate of adoption of definitions of nearly zero-energy housing concepts in the Netherlands, the Flemish Region and the Brussels Capital Region
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Conclusion

Definitions for highly energy-efficient housing have been introduced through general terms and demonstration projects and have been adopted and refined by innovators, researchers, business networks, mixed business/policy networks and policy developers. In search of defining nearly zero-energy dwellings, international researchers are currently proposing prominence of the terms ‘net zero energy’ and ‘net zero carbon’ in addition to ‘low energy’ and ‘passive house’, in order to enable compatible regional market infrastructure development and innovation diffusion. Although definitions can have a different meaning in different regions and are poorly integrated internationally, a few countries have already adopted definitions in their building or fiscal policies.

The analysis shows that in Belgium and the Netherlands, ‘passive house’ cannot be neglected as a useful term, offering market and some policy acceptance, for the realisation of net-zero-energy or zero-carbon definitions in the future implementation of national energy policies. A clear definition compatible with the regional context is necessary to increase attractiveness and demonstrability. Though the reduction or offsetting of energy and/or emissions in nearly zero-energy definitions seems fairly straightforward, the complexity when examined in detail and when integrated in building energy performance regulations can be reduced.

An important challenge to avoid market confusion is that targeted definitions are clearly formulated and used consistently at all political levels, national and regional. Whilst the research shows that new terms have been easily introduced, a huge effort lies in providing—and reducing the complexity of—associated evaluation procedures and in improving compatibility with local legislation and the recast of the energy performance of buildings directive. The Belgian situation provides an example of a legal framework, compatible with the required EPBD recast, in order to reward better energy performance for passive houses and zero-energy houses. It shows that early fiscal tools can be used to reduce market confusion and to try out or enforce definitions for highly energy-efficient houses.

A challenge now remains in providing a system of appraisal, especially with regard to compatibility with market initiatives and regional grant schemes, regional implementation of the recast of the EPBD, administrative control of tax relief and other energy-related issues (e.g. calculation of relevant energy indicators and tools, indoor climate appraisal and so on). These quality appraisal systems will be an important subject of future research.