Planning policy - section 3F: research

2. Literature Review

2.1 GHG Emission Reduction

2.1.1 Action on Global GHG Emissions

It is widely acknowledged that substantial and sustained action to reduce global greenhouse gas (GHG) emissions is required to prevent damaging climate change (IPCC, 2014). There are signs that efforts made in this respect are slowly beginning to stabilise global GHG emissions, albeit at a level that is 60% greater than in 1990 (Jackson et al., 2017; Ritchie and Roser, 2019). However, it has been calculated that global GHG emissions would need to fall by 7.6% every year over the next decade simply to limit global warming to a 1.5°C rise (Evans, 2020). Based on currently implemented climate policies a projected warming of 3.1 to 3.7°C is likely by 2100 (Ritchie and Roser, 2019). Accelerating action to reduce GHG emissions is therefore essential.

With growing recognition that urgent action is needed; over two thirds of District, County, Unitary & Metropolitan Councils in the UK have declared a climate and ecological emergency, and the UK as a whole has legally committed to achieving net-zero emissions by 2050 (BEIS, 2019b; Climate Emergency UK, 2020). In line with recommendations from the Committee for Climate Change (CCC) which highlighted that Scotland had a greater potential capacity to remove GHG emissions from the atmosphere than the rest of the UK through a program of reforestation; the Scottish Government has gone further and set a target of reaching net-zero emissions by 2045 (CCC, 2019a, p15; Institute for Government, 2020). These more ambitious targets necessitate a steeper rate of reduction in emissions than has been previously achieved. The Committee on Climate Change advise that to meet this target UK emissions will need to fall by 15 MtCO₂e every year. To put this in perspective, this is equivalent to 3% of all UK GHG emissions in 2018 (CCC, 2019c, pp 17-18).

The UK GHG emissions for 2018 were 491 MtCO₂e. This represents an overall emission reduction of 40% since 1990 (CCC, 2019c, p19). The four highest emitting sectors were respectively surface transportation (115 MtCO₂e), industry (104 MtCO₂e), buildings (88 MtCO₂e) and power (65 MtCO₂e). In 2018 these accounted for approximately 76% of all UK GHG emissions (CCC, 2019c, pp 24-27). Progress in reducing UK GHG emissions in the five years between 2013 and 2018 has been primarily driven by the power sector, with emissions from this sector 68% below 1990 levels (CCC, 2019c, p27). However, to achieve net-zero targets progress needs to be made consistently across all sectors of the UK economy.

2.1.2 Impact of the Built Environment on GHG Emissions

In 2016, buildings were on average accountable for 41% of the final energy consumption and 60% of the electricity consumption in EU-28 countries; Residential buildings accounting for two thirds of this consumption (458 Mtoe) (Rousselot, 2018). Reducing CO₂ emissions from the building sector is therefore crucial, and it is recognised as one of the most cost-effective ways to mitigate climate change (Grove-Smith et al., 2018).

In acknowledgement of the impact buildings have on GHG emissions, the European Parliament passed European Directive 2002/91/EC which was subsequently recast as European Directive 2010/31/EU on the Energy Performance of Buildings (EPBD). Article 9 of this legislation requires that all new public buildings must be nearly zero-energy by the end of 2018, and all other new buildings be nearly zero-energy by the end of 2020 (EC, 2018). Article 2 describes nearly zero-energy buildings as having a very high energy performance, with the remaining nearly zero or very low amount of energy still required being supplied to a very significant extent by energy from renewable sources, produced on-site or nearby (EC, 2018). The exact definition of a nearly zero-energy building has been determined independently by each EC member state and varies widely across EC-28 countries (EC, 2013). There is concern that some national building codes across member states do not comply with the sentiments expressed in the EPBD (Groezinger et al., 2014; Erhorn and Erhorn-Kluttig, 2018). Nevertheless, the design principles and technologies requisite to achieving this level of performance in new buildings are relatively well-established and readily accessible to the construction industry.

With the Paris Agreement on Climate Change in 2016 demanding a more ambitious built environment strategy, initiatives have been growing worldwide to accelerate the transition towards a fully decarbonised building stock (UNFCCC, 2020). Encouraging major and deep renovations as well as new construction to strive for a nearly zero-energy level of performance will be crucial in achieving this aim. However to minimise our environmental footprint, and create ecological and sustainable places for future generations, a significant and fundamental change is needed in the way we design, build, inhabit, maintain and deconstruct our built environment. The need for change is now accepted by most stakeholders and there is general agreement on the benchmarks for reducing both operational and embodied energy in buildings that will take the construction industry on the steep decent towards net-zero emissions by 2050 (RIBA, 2019a; UK Green Building Council, 2019).

2.1.3 GHG Emission Reduction in Scotland

The Climate Change (Emissions Reduction Targets) (Scotland) Act 2019, amended the existing Climate Change (Scotland) Act 2009, and revised the year by which Scotland aims to reach net-zero emissions, i.e. 100% emission reduction relative to the baseline level of 1990, to 2045. The act also set more ambitious interim emission reduction targets of at least 56% lower than the baseline by 2020, 75% by 2030 and 90% by 2040 (Scottish Parliament, 2019a).

The development of renewable energy resources is seen as critical to achieving these aims. In the 2020 Routemap for Renewable Energy in Scotland, published in 2011, the Scottish Government committed to generating an equivalent of 100% of Scotland's gross electricity consumption from renewable sources by 2020, and achieving targets of 11% renewable heat and 10% renewable transport (Scottish Government, 2011). In 2017, the Scottish Energy Strategy extended and strengthened these ambitions, with plans to almost completely decarbonise the Scottish energy system by 2050 through the large scale transition to low carbon and renewable transport and further expansion of renewable energy generation (Scottish Government, 2017a).

Progress in achieving these objectives has been steady. The Committee for Climate Change recently reported that in 2019 the GHG emissions in Scotland were 47% lower than the 1990 baseline set by the Climate Change (Scotland) Act 2009. The majority of this reduction has been driven by reforming the power sector (CCC, 2019b, p11). In 2019 Scotland generated 30,521 GWh of electricity from renewable energy sources; this represents 90.1% of gross electricity consumption in Scotland (Scottish Energy Statistics Hub, 2020d).

However it should be noted that across all sectors, more than 80% of total energy consumption in Scotland is still attributable to the burning of fossil fuels, with renewables supplying just 17.8% of overall demand (Royal Society of Edinburgh, 2019). Further, the Royal Society of Edinburgh's (2019) Enquiry into Scotland's Energy Future identified the need to improve energy security by increasing capacity, diversifying the range of energy storage options, developing a clearly articulated position on security of supply and deciding whether domestic energy-generating capacity should be increased.

2.1.4 Reducing Emissions from Buildings in Scotland

With respect to reducing GHG emissions from buildings, progress has been more protracted; with Sullivan's instructive report (Sullivan, 2007, 2013) providing recommendations for improving the energy performance of buildings in Scotland in order to reduce CO₂ emissions. It advocated a staged approach to delivery, with progressive tightening of energy standards and the adoption of backstop levels for U-values and airtightness in building fabric equating to those of Nordic countries. The primary objective was to deliver net zero carbon buildings (i.e. space and water heating, lighting and ventilation) by 2016/2017, if practical (Sullivan, 2007). This broadly aligned with the UK Government strategy for delivering Zero Carbon Homes by 2016 (Ares, 2016). There was also a long-term ambition to achieve total-life zero carbon buildings by 2030 i.e. all new buildings should be responsible for net zero emissions over their entire life including construction, use, maintenance and demolition (Sullivan, 2007).

The update of the Sullivan Report (2013) recognised the impact of the 2008 Financial Crisis and the additional challenges this imposed on the construction industry. Although the need to mitigate climate change was still considered pressing, the timescale of regulatory change was revised to provide a longer lead-in time for improving building energy standards and the programming of these to align with commitments set out in Article 9 of the recast Energy Performance of Buildings Directive (2010/31/EU) which required all new buildings to be nearly zero energy by the end of 2020 (Scottish Government, 2013; EC, 2018). Following the withdrawal of the UK's ambitious building emission reduction targets in 2016, progress in implementing more onerous standards for full decarbonisation of regulated energy use in buildings has been relatively slow.

Both the original and updated Sullivan Reports perceived decarbonising the UK energy supply and increasing the energy efficiency of buildings as more reliable long-term strategies for reducing CO₂ emissions from new buildings, than the use of building-integrated LZCGT (Sullivan, 2007, 2013). This view was formed due to the relative immaturity of the technologies involved, their associated cost and the limited knowledge and skills base present in the industry at that time. There was concern that mandating the use of LZCGT in new buildings would discourage development and be particularly detrimental to the provision of affordable housing (Sullivan, 2007). The Sullivan Reports also raised the issue of potential conflict between Planning (Section 3F Policy) and Building Standards over this issue (Sullivan, 2007, p26-27; 2013, p11).

However other research at that time contended that if the technical barriers to adopting microgeneration were addressed, then the widespread installation of LZCGT could potentially provide 30 to 40% of Scotland's electricity needs by 2050; effectively reducing annual household CO₂ emissions by 15% (Scottish Executive, 2007, p19). Promoting the microgeneration of heat and/or electricity from LZCGT was therefore seen as central to meeting Scotland's long-term obligations and aspirations in relation to GHG emission reduction (Scottish Executive, 2007; Scottish Government, 2009).

Published in 2009, the Renewable Heat Action Plan for Scotland promoted the use of renewable heat technologies ranging in scale from individual building systems to district heating schemes (Scottish Government, 2009). This was supported in 2014 by the UK wide Renewable Heat Incentive which offered financial incentives to householders, communities and businesses to encourage uptake of renewable heat technologies (Energy Saving Trust, 2020). Microgeneration of electricity from renewables was also encouraged and financially supported through Feed-in Tariffs (FIT) (Ofgem, 2020).

Whilst not all targets have yet been fully realised, Scottish government policies and improved building standards have delivered substantial GHG emission reduction in this sector. Direct emissions from Scotland's buildings in 2017 amounted to 8.3 MtCO₂e, or 20% of Scotland's total GHG emissions. This represents an overall fall in GHG emissions from buildings of 24% relative to 1990 levels (CCC, 2019b, p67). It should be noted that there are year on year fluctuations in this figure due to prevailing weather conditions. Improvements in Building Standards have had a particularly significant effect, with CO₂ emissions from new domestic buildings now typically 75% lower than they would have been if built to the construction standards applicable in 1990 (Scottish Government, 2018a, p85).

2.1.5 Future GHG Emission Reduction Targets

In addition to the aforementioned intention of Scotland to reach net-zero emissions by 2045, the Scottish Government has established other targets in relation to future energy generation and GHG emission reduction (Scottish Parliament, 2019a). In 2017, the Scottish Energy Strategy: the future of energy in Scotland set a new policy target for 2030, requiring the equivalent of 50% of all energy consumption for heat, electricity and transport to be supplied from renewable energy sources (Scottish Government, 2017a).

The following year, Scotland's revised Climate Change Plan set out policies for the period between 2018 and 2032 (Scottish Government, 2018a, pp 80-101). These include an ambition to supply 35% of heat for domestic buildings using low carbon technologies where technically feasible by 2032. In non-domestic buildings the equivalent ambition is 70% of heating and cooling demand. There is also an intention to insulate buildings to the maximum appropriate level; with improvements in fabric energy efficiency anticipated to deliver 15% and 20% reductions in heat demand in domestic and non-domestic buildings respectively by 2032.

The Climate Change Plan also highlights that overall electricity consumption is expected to increase because of efforts to decarbonise heat and transport, and this will place additional burdens on the electricity sector and the supply network (Scottish Government, 2018a). Whilst renewable electricity generation is expected to expand to meet this demand; it is also recognised that policies that aim to reduce energy demand, increase in-use energy efficiency and promote the appropriate deployment of small scale renewable energy generation are also requisite to reduce pressure on the centrally generated electricity supply and ensuring long-term energy security.

2.2 Key Factors Determining GHG Emissions from Buildings

There are a number of factors that affect the level of GHG emission from buildings. The impact of some are relatively simple to identify, quantify and take appropriate action on e.g. fabric energy efficiency, equipment efficiency, LZCGT, and the use of renewable energy in national energy networks. Other factors require deeper deliberation to appreciate and understand their impact e.g. passive architectural design and changes in societal demands, expectations and aspirations. How these factors interact is not always obvious at the outset, and the results of actions taken are not always exactly as expected (Copiello, 2017).

2.2.1 Societal Demands, Expectations and Aspirations

Many of the societal changes that are currently happening on a global scale effectively increase energy demand and counteract efforts to reduce global GHG emissions. Societal factors that have a negative impact on energy used in buildings include increased urbanisation, population growth, a decrease in size but an accompanying increase in the number of households, increases in per capita heated living space, enhanced expectations of thermal comfort, increased reliance on technological devices, greater consumerism and general aspirations for a more affluent western lifestyle (Urge-Vorsatz et al., 2013; Grove-Smith et al., 2018). Many of these factors have an obvious impact on the regulated energy consumption of buildings i.e. energy used for space heating, hot water, lighting and ventilation. However aspirations for a more affluent lifestyle, consumerism and the ubiquitous use of technology can also result in substantial increases in the currently unregulated operational and embodied energy demand of buildings.

An example of the influence societal aspirations have on energy use can be seen in the changes in energy consumption patterns in the UK. In 2018, 5,360 ktoe (12.8%) of energy consumption in domestic buildings was attributed to household electrical appliances. Palmer and Cooper (2014) suggest that this amount has roughly tripled over the past 40 years in the UK. The main factors contributing to this increase in unregulated electricity use are: the proliferation in the number and type of home electrical appliances (e.g. washing machines, tumble dryers, dish washers, TVs and entertainment consoles, computers, personal electronics, chargers etc.); the larger size and much greater use of cold appliances to store food (large 'American style' fridges and freezers); and the increased use of all these items (actual use and standby electricity) ( Palmer and Cooper, 2014, p38-39).

Of course societal influences can equally have a positive impact and encourage change that will be beneficial to the environment. For example the concept of a 2000 Watt Society developed in 1998 by the Swiss Federal Institute of Technology recognised that the current level of consumption in developed countries is unsustainable and that we each need to take more responsibility for our choices, and use only what is a fair and equitable share of the world's resources (Morosini, 2008; Stulz et al., 2011). It envisaged an 'energy-sober society' where total primary energy use per capita is limited to the global average of 17,520kWh/annum without any attendant loss in the quality of life (Morosini, 2010). Whilst various critics have argued that the metric does not take into account the quality of the energy consumed, others argue that setting an aspirational limit to overall energy consumption would avoid potential rebound effects and incentivise individuals to re-examine their relationship with energy across all aspects of their lives and hopefully make appropriate changes to their lifestyles. At the very least it opens a discussion about unfettered energy consumption.

It should also be recognised that measures taken to reduce GHG emissions may not deliver as extensive an impact as might be expected because of the interplay of sociological factors in the real world. For example, studies have looked at the impact of improving fabric energy efficiency on overall GHG gas emissions. In these circumstances, increased fabric energy efficiency has a positive impact peoples' lives, initially reducing energy consumption, energy bills and fuel poverty, whilst simultaneously improving health, comfort and well-being. However, lower energy bills eventually result in increased disposable income, which in turns leads to greater consumerism and energy consumption in other areas of life. This is known as a rebound effect or Jevon's Paradox, and can result in actions taken to reduce GHG emissions failing to reach their expected potential (Copiello, 2017).

2.2.2 Passive Design

DeKay and Brown (2014), have been long-standing proponents of reducing energy consumption and emissions from buildings using passive architectural design strategies. In their seminal book 'Sun, Wind and Light' they suggest a hierarchy of strategies for attaining net-zero energy buildings that prioritises actions that are low technology and low cost, and which substitutes the 'embodied intelligence in architectural form for hardware' (DeKay and Brown, 2014) (Figure 1). This pyramidal diagram is not intended to infer a strict sequence of decision making, but rather imply that each higher level depends on decisions made at lower levels. For example, it is considered better to use site design to create a favourable microclimate and reduce environmental stresses on a building, before trying to use building design or technologies to solve problems that the building need not actually face. This passive design approach aligns with prevailing wisdom that to achieve net-zero energy buildings it is necessary to first reduce energy demand and increase energy efficiency to enable the cost-effective use of renewable technologies (Urge-Vorsatz et al., 2013; Grove-Smith et al., 2018). Where it might diverge from some of that literature is in identifying architectural design as the critical component that is too often absent in achieving this aim.

Passive design measures are not complicated or difficult to incorporate into the built environment, but they do need to be considered early in the design process. They might require that the appropriateness of the scale, form factor or solar access of the proposed building be reassessed (Cotterell and Dadeby, 2013; DeKay and Brown, 2014; Burford et al., 2019). Alternatively they might involve re-evaluating the site layout and incorporating landscape elements into the design to create a more favourable microclimate. Trees or other vegetation might be used to create shelter and shade while simultaneously reducing sound propagation, improving air quality, sequestering carbon and creating pleasant outdoor spaces (Harris and Borer, 1998). The thermal mass of building materials might be employed to effectively store heat, moderate temperature fluctuations or induce air movement. Orientating a building and most of its windows towards the south maximises the potential for solar gain and daylighting, but the architectural detailing of the windows and their surrounds can also have a significant impact on how well this is controlled (DeKay and Brown, 2014). Thoughtful forward planning might also be applied by orientating roof surfaces towards the south to accommodate future solar thermal or PV panels, enabling the building to be retrofitted to higher standards later in its life.

Unfortunately the potential of architectural design to make a meaningful contribution to emission reduction is not currently being given the priority and level of consideration it deserves. Most planning authorities do recognise the impact that these types of measures can have on energy consumption and GHG emissions, and actively promote sustainable and passive design approaches alongside Section 3F policy within their local development plans. However there appears to be little change in general building practices that would suggest that these measures are actually systematically employed.

The issue may simply be that the impact of passive design measures requires a more nuanced and deeper understanding of architectural design, the interactions between a building and its immediate environment, and the extent to which that environment can be manipulated to create more favourable microclimatic conditions. It is therefore not as easy and straightforward for policymakers to quantify and legislate for, in comparison to the technological efficiencies of the building fabric or equipment. Furthermore there are no mandatory standards setting a limit to either space heat demand or building energy demand in the UK. The Standard Assessment Procedure (SAP) used to determine whether a proposed dwelling has achieved the required CO₂ emission reductions, does so by comparison to a 'notional dwelling' built to specified technical standards. This notional building is described as having the same size, shape and living area fraction as the proposed dwelling (Scottish Government, 2019a). This not only fails to incentivise the use of passive architectural design as a critical and cost-effective means of achieving net-zero energy building, it effectively removes it from the calculation.

2.2.3 Fabric Energy Efficiency (FEE)

In the UK in 2018, energy consumed for space heating in the domestic, industrial and services sectors was 38,547 ktoe, or 46.6% of their total energy consumption (BEIS, 2019a, Table U1). The majority of this, 27,144 ktoe, was consumed in domestic buildings and represents 64.8% of their total energy consumption (BEIS, 2019a, Table U3). Given these proportions it is evident that to make a significant impact on reducing CO₂ emissions from buildings it is essential to reduce and/or decarbonise the energy used for space heating (Palmer and Cooper, 2014, p.35-36).

Increasing the fabric energy efficiency of a building by improving insulation, minimising thermal bridging and increasing air-tightness is therefore an obvious action to take to reduce CO₂ emissions from buildings. This is easier to accomplish during the initial construction of the building, with the cost being only about one-fifth of that incurred by retrofitting to the same quality and standard at a later date (CCC, 2019d, p14). Furthermore, failure to take action now risks constructing buildings that, without costly retrofitting, will underperform throughout their entire life and effectively lock a certain level of CO₂ emission into the built infrastructure for decades to come. Numerous scenarios predicting global energy use and CO₂ emissions have documented this carbon lock-in effect, and initially it was thought that Western Europe would mostly avoid it because of rapid moves to decarbonise (Urge-Vorsatz et al., 2013; Berardi, 2016; Grove-Smith et al., 2018). However progress has been slower than predicted because many proposed policies were either withdrawn before implementation or their ambitions curtailed in the aftermath of the global financial crisis of 2008 (Erhorn and Erhorn-Kluttig, 2018).

It is therefore essential that all new buildings are designed to the highest fabric energy efficiency standards, so that their environmental impact in the long-term is as small as possible (Willmott Dixon, 2020). Acknowledging this the Committee for Climate Change recently advised that all new homes should deliver ultra-high levels of energy efficiency as soon as possible and by 2025 at the latest. This proposed ultra-high level of energy efficiency was considered consistent with a space heat demand of 15 to 20kWh/m².annum (CCC, 2019d, p14).

However, the larger challenge that needs to be addressed in order to achieve net-zero emissions is not predicated on the energy standards in new buildings, but on how to bring the existing building stock up to a similar level of energy efficiency. In Scotland, new buildings have had to comply with minimum standards for energy efficiency and airtightness since 1982, and in the intervening decades these building standards have been regularly improved (Scottish Government, 2017b; Scottish Government, 2019a; Scottish Government, 2019b). However, 75% of Scotland's occupied dwellings were built before 1982, and 20% were built before 1919 (Scottish Government, 2017b). This ageing and varied building stock presents a significant challenge because of the scale of investment required and the physical and technical difficulties involved in bringing them in line with contemporary expectations (Royal Society of Edinburgh, 2019).

In response, Scotland designated energy efficiency as a national infrastructure priority in 2015 and has made clear progress with the Energy Efficient Scotland programme in setting targets and proposing financial support packages (Scottish Government, 2018b; CCC, 2019b). The objective is for all Scottish homes to achieve an Energy Performance Certificate (EPC) band C or better by 2040 where technically feasible and cost effective (Scottish Government, 2018b). The current programme has so far focused on social housing and the private rented sector and has made a greater per household investment in energy efficiency schemes than the UK average, however further measures for owner occupied homes are not anticipated until after 2021 (CCC, 2019b).

2.2.4 Low and Zero Carbon Generating Technology (LZCGT)

In its definition of nearly zero-energy buildings the Energy Performance of Buildings Directive (EPBD) clearly envisions that these buildings will have a very high energy performance with any remaining energy demand being very small and met substantially by energy from renewable sources, produced on-site or nearby (EC, 2018, Article 2). To enable this, the on-going development and maturation of small scale renewable energy technologies has been supported by successive governmental policies through Feed-in Tariffs (FIT) and the Renewable Heat Incentives (RHI) (Energy Saving Trust, 2020; Ofgem, 2020). These have sought to create cost effective renewable energy solutions and promote the normalisation of their use within the building sector. Section 3F also supports this objective, requiring planning authorities to include policies within their local development plans, which ask all new buildings to install and operate LZCGT. Further it states that the use of these LZCGT should be responsible for avoiding a specified proportion of the buildings predicted GHG emissions. This proportion is to increase over time (Scottish Parliament, 2019b).

Building Integrated Solutions

From the perspective of electricity generation potential renewable energy technologies include photovoltaics (PV), wind, hydro and biomass combined heat and power (CHP). PV is seen as being the most practical and cost-effective building-integrated solution, with the ability to simultaneously contribute to the decarbonisation of the national grid and reduce grid demand from buildings (BRE, 2016b; Osseweijer et al., 2018).

From the perspective of heat generation potential renewable technologies include solar thermal, heat pumps, deep geothermal , biomass primary combustion, biomass combined heat and power (CHP), biomass fuel cells, energy from waste (EfW) which includes advanced conversion technologies (bio-methane to grid, anaerobic digestion CHP and anaerobic digestion heat production) incineration and landfill gas (Grillanda and Khanal, 2019). There are currently no recorded incidences of biomass fuel cell and deep geothermal in Scotland. Grillanda and Khanal (2019) also note that passive renewable heating i.e. solar gain should be considered a renewable energy heat source, but because of the difficulty in assessing its contribution to heating demand it is not currently captured in the Renewable Heat Database.

In 2018, Scotland generated an estimated 6.3% of its non-electrical heat demand from renewable sources (Grillanda and Khanal, 2019). The aim is to achieve 11% by 2020 (Scottish Government, 2011; CCC, 2019b). The majority of this was generated through biomass primary combustion and biomass combined heat and power (CHP). Together, these two technologies account for 3,850 GWh (73%) of all renewable heat output and 1.66 GW (83%) of capacity (Grillanda and Khanal, 2019, p7). These figures include large installations (> 1MW), small to medium installations (between 45kW and 1MW) and micro installations (≤ 45kW). Building integrated systems will tend to fall within the micro category; district heating systems within the small to medium.

In 2018, micro-renewable heat generation accounted for just 18% of Scotland's total renewable heat capacity and 12% of annual output, but a total of 85% of all installations (Grillanda and Khanal, 2019, p24). The discrepancy between capacity and output is attributed to the fact that many micro-renewable heat installations are used more intermittently than larger commercial or industrial systems. In 2018 micro-renewable heat generation in Scotland provided an annual output of 634 GWh, which comprised of approximately 326 GWh (51%) from biomass primary combustion, 292 GWh (46%) from heat pumps and 16 GWh (3%) from solar thermal (Grillanda and Khanal, 2019).

Distribution and technological trends have been observed within the micro-renewable heat generation data. Of the heat installation accredited under the Domestic Renewable Heat Incentive in Scotland from April 2014 to December 2019, 89% of biomass, 89.6% of air source heat pumps (ASHP), 88% of ground source heat pumps (GSHP) and 64.6% of solar thermal installations were located in off gas grid locations (Scottish Energy Statistics Hub, 2020e). Further in the period between June 2019 and June 2020 the trends observed in the type of technologies being deployed in Scotland by the number of accredited applications under the Domestic Renewable Heat Incentive were; Air Source Heat Pumps (ASHP) increased by 23.5% (from 7,356 to 9,083 accredited applications), Ground Source Heat Pumps (GSHP) increased by 9.4% (from 1,328 to 1,453), Solar Thermal increased by 3.4% (from 1,192 to 1,232) and biomass decreased by 1.8% (from 3,825 to 3,758) (Scottish Energy Statistics Hub, 2020e). The rapid increase in the uptake of heat pumps is also borne out in the anecdotal data collected within the survey carried out for this research (Appendix A, Questions 15, 16 & 17).

Pertinent to the discussion of micro-renewable heat generation is that the Committee on Climate Change (2018) has recently concluded that the current uses of biomass need to change to increase carbon sequestration and storage. This will entail a transition towards biomass being used in construction and bioenergy with carbon capture and storage (BECCS) and away from biomass for heating buildings or biomass for generating power without carbon capture and storage. They have therefore recommended that the UK should limit future support for bioenergy use in buildings to bio-methane from anaerobic digestion (CCC, 2019b).

Local Energy Networks

The Scottish Government aspires to a smarter and more coordinated approach to planning and meeting local energy needs. To facilitate this, it has developed a Local Heat & Energy Efficiency Strategies (LHEES) framework. The aim of which is to have local authorities work closely with their communities to set out a long-term prospectus for investment in new energy efficiency, district heating (heat networks), and other heat decarbonisation programmes at a local level (Scottish Government, 2017a).

The advantage heat networks offer over building integrated systems is that they are dynamic entities, not completely tied to any single energy generating source. This flexibility allows them to grow and change in relation to shifts in energy needs or the development of new technologies (Royal Society of Edinburgh, 2019; District Heating Scotland, 2020). By aggregating heating and cooling demands across multiple buildings heat networks can also make the most efficient use of locally available renewable and waste energy resources, and employ renewable technologies which would not be viable options for individual buildings. Heat networks also have the potential to temper the peak winter demands on the national electricity grid which would be exacerbated by the mass uptake of individual heat pumps (Royal Society of Edinburgh, 2019).

Renewable heat technologies that could realistically contribute to district heating systems might include: air source heat pumps (ASHP), ground source heat pumps (GSHP), water source heat pumps (WSHP), biomass combined heat and power (CHP), solar thermal with seasonal thermal energy storage (STES), energy from waste (EfW), hydrogen, geothermal (disused mines, sedimentary aquifers and granite), waste heat from industrial or commercial processes, waste water heat recovery (WWHR), and utilizing surplus electricity from intermittent renewables (Royal Society of Edinburgh, 2019; District Heating Scotland 2020).

The economic viability and carbon saving potential of district heat networks will ultimately depend on locally available energy resources and the density and diversity of heat demand (Royal Society of Edinburgh, 2019). They are particularly suited to dense urban areas, but can also provide solutions in some rural contexts by enabling the development of local renewable heat sources. Whilst the implementation of district heating might be limited by context, it is envisaged that it will meet at least 10% of residential and service sector demand in the future (Royal Society of Edinburgh, 2019). There are however a number of financial and regulatory constraints that would need to be addressed to facilitate their wide-scale uptake (Appendix A: Questions 18-20).

2.2.5 National Energy Networks

In 2016 almost 50% of all energy consumed in Scotland was supplied via the national gas and electricity networks. This includes 86% of domestic energy consumption. Ensuring these networks can continue to supply affordable energy on demand to everyone across Scotland while the energy they supply is gradually decarbonised is essential to Scotland's future energy security (Scottish Government, 2019d).

The Gas Network

Gas networks in Scotland currently connect to approximately 80% of households and deliver a secure and comparatively low cost energy supply. These extensive networks effectively provide an energy storage capacity several hundred times greater than anything that could be developed in relation to the electricity grid (Scottish Government, 2019d). The inherent storage capacity of the gas network allows it to easily absorb large swings in daily demand and in doing so it supports the wider energy system.

The UK is currently investigating the possibility of decarbonising the gas supply and how this might be safely achieved. At present this work is exploring the technical implications of incrementally blending low carbon gases (bio-methane and bioSNG) and hydrogen with the natural gas within the existing network (Carbon Connect, 2017). 15 bio-methane sites are already connected to the gas grid in Scotland (Scottish Government, 2019d).

Other work is also examining the technical feasibility and potential cost implications of converting natural gas networks to 100% hydrogen after 2030, in line with the hydrogen based future energy scenario identified as one potential path to achieving the 2045 net-zero emission target (Scottish Government, 2017a; Scottish Government, 2019d). A 100% hydrogen grid is unprecedented. This would therefore be a more radical solution which would require all pipes to be converted to polyethylene (this is on-going and due to be completed by 2032) and the replacement of consumer gas appliances with hydrogen compatible ones (Carbon Connect, 2017).

To what extent the gas grid could be successfully decarbonised is still debateable. The carbon intensity of low carbon gases and hydrogen vary depending on their feedstock, production method, energy used in the production process and the effectiveness of carbon capture (Carbon Connect, 2018). For example producing bio-methane from food waste has lower emissions than producing it from energy crops, as well as avoiding potential conflict over the use of land that could be used for food production. Many of the processes for producing low carbon gases and hydrogen are still in their development stages and the carbon intensity of these processes is as yet uncertain (Policy Connect, 2018).

The Electricity Grid

In the 12 months to June 2020, 86.5% of the electricity consumed in Scotland was generated from low carbon sources - 56% from renewables and 30.5% from nuclear (Scottish Energy Statistics Hub, 2020a). For the UK as a whole the carbon intensity of the electricity grid in 2018 was calculated as 200.7 gCO₂e/kWh. In Scotland the carbon intensity in 2018 was 44.6 gCO₂e/kWh; a rise from the 24.0 gCO2e/kWh recorded in 2017; due to the prolonged power outages associated with Hunterston B nuclear power station (Scottish Energy Statistics Hub, 2020b).

In 2019, 30,521 GWh of electricity was generated from renewable energy sources in Scotland (Scottish Energy Statistics Hub, 2020d). In order of prominence this was comprised of: 19,143 GWh from onshore wind; 5,362 GWh from hydro; 3,182 GWh from offshore wind; 2,031 GWh from biomass (including co-firing); 412 GWh from landfill gas; 347 GWh from solar PV; 29 GWh from sewage sludge digestion; and 14 GWh from wave/tidal (Scottish Energy Statistics Hub, 2020c). Although only the first quarterly figure for renewable electricity production in 2020 is available, this saw an increase of 28% relative to the same quarterly period in 2019 (Scottish Energy Statistics Hub, 2020c).

Notwithstanding these achievements, realising net-zero emissions by 2050 will have a profound effect on the UK's electricity grid. The drive to decarbonise transport and heat will almost certainly result in a precipitous rise in the use of electric vehicles and heat pump technology, and a rapid increase in electricity demand. As a result it is expected that UK electricity generation will need to double from 300 TWh to around 600 TWh by 2050 (CCC, 2019b, p95). Without a corresponding increase in low carbon generation there is every possibility that these demands would have to be met by gas-fired generation. To ensure that this does not happen and that the anticipated increase in electricity demand can be met without increasing emissions the Committee for Climate Change has recommended that the UK electricity network as a whole should aspire to a maximum emission intensity of 50g CO₂e/kWh by 2030. To achieve this target will require a substantial increase in new renewables as well as technologies such as nuclear and carbon capture and storage (CCS) (CCC, 2019b, pp. 42-43).

Higher electricity demands coupled with the increased use of intermittent renewable energy sources will necessitate improvements in system flexibility and widespread upgrades in terms of capacity and transmission networks. To enable Scotland to realise its renewable energy potential large scale investment is currently being delivered by a series of network development and reinforcement projects (CCC, 2019b, p96).

The management of energy flows and reducing demand side requirements are recognised as critical to maintaining the affordability and security of the electricity supply whilst the grid is decarbonised. To achieve greater flexibility, manage increasing peak demands, tighten capacity margins and overcome the intermittency issues associated with renewable generation the development of energy storage capacity is critical (Millar, 2015). This could be integral to the electricity grid or incorporated into local energy networks or buildings, and could be either in the form of electricity or heat (Abegg, 2011).

This also raises questions concerning the design of building energy systems and the appropriateness of different technology types in supplying the different building energy requirements. In the raft of the many available building energy policies, Hermelink et al. (2013) highlights a lack of attention to and a mismatch in the design and energy demand of new buildings and their interaction with the energy grid; with Hogeling (2012) stating the assumed infinite capacity and storage in the grid was a failure to account for timing of electricity generation and use.

2.3 Priorities in New Buildings

The primary objective of this research is to ascertain what would be a reasonable level of emission reduction that could be sought by Section 3F Policy through the use of LZCGT in new buildings within the Scottish context. As we have seen there are several factors that actively contribute to the level of GHG emission from buildings. These include societal influences, passive design solutions, fabric energy efficiency, building services equipment efficiency, building integrated LZCGT and the prevalence of renewable energy within local and national energy networks. Determining which factors should be prioritised and in what proportion to attain both a rapid and continuing long-term decarbonisation of the building sector without stifling potential architectural innovation is a more complex matter.

2.3.1 Architectural Innovation

The difficulty of assigning a numerical value to the contribution LZCGT should make to GHG emission reduction is that every building is different, and if this level is set too high there is the potential to stifle architectural innovation that may result in more cost effective long-term solutions. This is perhaps best illustrated by considering two buildings: the R128 House and the 22-26 Building (Blaser and Heinlein, 2002; Eberle and Aicher, 2016). While both concepts are at the cutting edge of ultra-low emission building design, and each delivers a sustainable and nearly zero-energy outcome, they start from very different philosophical positions and take vastly different approaches (Figure 2).

The R128 house (Germany, completed 2002) is an emission free highly automated house requiring no energy input for heating and is completely recyclable. The all-glass facade which provides complete transparency has a comparatively poor U-value compared to conventional building facades that aim to conserve energy through using high-performance thermal envelopes. Instead R128 relies on renewable power generating systems, mechanical ventilation and a heat store to manage the comparatively large diurnal and seasonal fluctuations in temperature to ensure constant indoor climatic conditions. The electricity grid is used as an energy store by feeding in surplus energy from the solar panels and tapping it when there is a shortfall – this assumes that any carbon intensive energy drawn from the grid is replaced by renewable energy generated at the building. The PV generating system produces surplus energy over the lifetime of the building which is sufficient to cover the operational energy and embodied energy costs of the prefabricated, demountable construction system and its recycling.

By contrast, the 22-26 Building (Austria, completed 2013) is notable in its apparent simplicity as there are no mechanical environmental systems and no active heating equipment. Instead, it relies on a very high thermal mass and sensor operated windows to control indoor temperature and ventilation, with heating coming from solar gain, equipment and occupants. The dynamic behaviour of the solid exterior wall construction combines high heat flow resistance and high thermal capacity to manage indoor climatic conditions and control heat loss. Most of the construction materials were sourced locally and chosen because of their minimal need for processing from their natural state, thereby reducing their embodied impact. While the 22-26 Building does not attempt to employ LZCGTs to cover other energy uses such as lighting and plug load it is clearly a very low-impact, low-emission form of construction. The approach taken by the 22-26 Building is further justified by its notably low construction costs of about 1200 €/m² as a result of its simplicity and lack of applied technology. In comparison R128 is technically sophisticated and the building services are likely to prove costly both in initial outlay and in their on-going maintenance and eventual upgrade.

2.3.2 Holistic Approach with Hierarchy of Actions

The consensus among academics and construction industry figures is that the most effective way to reduce GHG emissions from buildings is to tackle the problem from a holistic perspective rather than fixate on any single contributing factor (Sullivan, 2007; Urge-Vorsatz et al., 2013; Beradi, 2016; Grove-Smith et al., 2018; Scottish Government, 2019a). This approach perceives buildings as systems that can be optimised with respect to design, efficiency, economy and contextual opportunities and constraints, in order to deliver the most appropriate emission reduction strategy. This does not preclude certain factors in general being strategically prioritised.

Governments however also need to take into consideration the wider interactions of buildings with the existing energy infrastructure, how these relationships and infrastructures are changing due to ongoing decarbonisation and the projected increase in energy demand from other sources such as electrical vehicles. Seen from this perspective the government needs to develop logical strategies in relation to energy use in buildings that will maintain energy security whilst simultaneously taking the country on the rapid decent to net-zero emissions by 2045.

Urge-Vorsatz et al. (2013) submit that strategically the best long-term solutions to reducing GHG emissions from buildings should include the following hierarchy of actions:

i. Reduce energy demand:
From a sociological viewpoint, this might involve supporting positive lifestyle or behavioural changes. From the perspective of building design it might include the consideration of passive design solutions or increasing building fabric energy efficiency.

ii. Increase efficiency of energy use:
All aspect of the design, construction, and occupational phases should be considered. This might include investigating the embodied energy of building materials, more efficient construction methods, ways to minimise building energy losses or utilise heat recovery, the efficiencies of specific equipment and technologies, and the optimization and maintenance of building systems once occupied.

iii. Increase the use of renewable energy:
To maximise sustainability and reduce the impact on national energy infrastructures, these energy sources should preferably be generated locally.

The reasoning behind this approach is that to achieve ultra-low energy, net-zero energy or eventually positive energy buildings in a cost-effective way, it is first necessary to reduce the energy requirement of the building to the point that the remaining energy demands can be practically and economically met by renewable energy sources. This basic 3-point strategy underpins the approach taken by most governments and internationally recognised standards such as Passivhaus. In developed countries where demand for energy is very high and already exceeds globally sustainable levels, it is also suggested that further measures might be necessary to change attitudes and behaviours at a societal level; for example by developing policies that actively discourage wasteful excesses or cap individual energy usage (Morosini, 2010; Ettlin, 2013; Urge-Vorsatz et al., 2013).

In terms of specific actions that architects and building owners should focus on, the UK government has identified two priorities: increasing fabric energy efficiency and decarbonising heat (CCC, 2019b, d). Both these priorities can be seen to relate directly to the fact that in the UK in 2018, 56.7% (46,936 ktoe) of the total energy consumption in the domestic, industrial and service sectors (excluding agriculture and transport) was due to space and water heating. In the domestic sector this proportion rose to 81.7% (34,184 ktoe) of total energy consumption (BEIS, 2019a, Table U1).

2.3.3 Prioritising Fabric Energy Efficiency

Whilst supporting an integrated design approach which promotes GHG emission reduction through improvements in building design, fabric and services; most of the literature also advises prioritising the issue of fabric energy efficiency (Urge-Vorsatz et al., 2013). There are several reasons for this.

In our cold northern climate, the need for space heating tends to dominate energy demand. In 2018, it represented 64.8% (27,144 ktoe) of the total annual energy demand in the domestic sector in the UK (BEIS, 2019a, Table U3). Enhancing fabric energy efficiency; by improving insulation levels, minimising thermal bridging and increasing airtightness; is therefore the most obvious and cost-effective way to cut energy demand and CO₂ emissions in new buildings (Beradi, 2016).

It should be noted that at very high fabric energy efficiency levels there are balances to be made between the initial construction costs versus operational costs, and the embodied energy of the building materials versus the operational energy demand of the building. However the optimum point overall for both cost and energy appears to fall within the general descriptor of Passivhaus i.e. at an annual space heat demand of about 15kWh/m².annum (Copiello, 2017; Grove-Smith et al., 2018). This is primarily because of a shift in technologies at this point. At this very high level of fabric energy efficiency the use of mechanical ventilation becomes necessary to maintain indoor air quality during the heating season. However, if an efficient mechanical ventilation heat recovery (MVHR) system is employed the size of the heating system can be significantly reduced. This associated cost saving tends to largely offset the cost of improving the building fabric (Cotterell and Dadeby, 2013; Copiello, 2017; Currie and Brown, 2019).

On a national scale, taking a fabric first approach reduces the peak energy demand of the building, minimising the additional capacity that needs to be built into the national energy networks to meet peak winter demands and thereby supports long-term energy security (Currie and Brown, 2019). This matters, because in the absence of long-term storage options, the on-going decarbonisation of the national grid requires increased capacity to cope with the intermittency of renewable energy sources. Yet changing lifestyles, the switch to electric vehicles, and the increased use of heat pumps, will see electricity demands grow.

The timeframe over which emission savings can be reasonably expected to be made also needs to be considered. Increasing fabric energy efficiency effectively reduces operational energy demand and GHG emission over the entire lifetime of the building (>100 years), whilst the effect of specifying LZCGT will be limited to the equipment's operational lifespan (15 - 20 years). Furthermore poor fabric energy efficiency is much more difficult and costly to remedy at a later date than during the initial construction phase (CCC, 2019d, p14). This can lead to buildings that have failed to take a fabric first approach underperforming over their entire life and a certain level of carbon emissions being effectively locked-in to the built infrastructure (Urge-Vorsatz et al., 2013; Beradi, 2016).

On a purely practical level the substantial reduction in energy demand that can be achieved through improved fabric energy efficiency has an impact on the size and cost of energy systems required to meet this demand and can make the use of renewable energy systems more practical and affordable. For building occupants, increased fabric energy efficiency also reduces energy bills, increases disposable income and a positive impact on occupants' comfort, health and well-being (Payne et al., 2015; Copiello, 2017; IEA, 2019).

2.3.4 Decarbonising Heat

Different challenges exist for decarbonising heat in domestic and non-domestic buildings in Scotland. EPC data suggests that 50% of non-domestic buildings use electricity as their primary source of heat and only 42% use natural gas. Conversely in domestic buildings only 12% use electricity, whilst 79% use natural gas (CCC, 2019b). The use of natural gas in domestic building for space heating and hot water is almost ubiquitous if a connection to the gas grid is available. The development of a national strategy to decarbonise heat is considered essential if the UK is to meet the 2050 net-zero emission target (CCC, 2019b,d). This challenge can be approached from many different angles and several tactics have been developed that can be employed in different contexts.

At a national level:

i. Continue support for decarbonising the gas network through bio-methane injection.

ii. Support research into the possibility of repurposing the gas network for hydrogen.

iii. Continue to decarbonise and increase the capacity of the national electricity grid. This is essential to obtain the largest benefit from the deployment of technologies such as heat pumps, which typically consume one unit of electricity for every three units of heat they produce.

At a local level:

iv. Invest in building or extending low-carbon heat networks particularly in heat dense urban areas, large-scale new developments and some rural locations; assess prospective network location taking into consideration the available renewable energy opportunities, heat demand, capital costs and the level of householder engagement. The aim is to have approximately 1.5 million homes across the UK connected to heat networks by 2030 (CCC, 2019d).

v. Instigate a shift to bioenergy with carbon capture and storage (BECCS) for all medium to large scale biomass energy generation.

At a building level:

vi. Limit the support for bioenergy use in buildings to bio-methane produced from anaerobic digestion. The widespread use of solid biomass boilers is not consistent with the long-term decarbonisation of heat.

vii. During the 2020s; retrofit at-scale existing buildings on the gas grid with hybrid heat pumps (HHP). Hybrid heat pumps are capable of switching between electricity and a variety of other heat sources, and have the advantage that they can be retrofitted into an existing heating system without changing radiators and with the existing boiler acting as the supplementary heat source. As such they are considered a low regret choice. The householder could switch to a hydrogen boiler if the gas network is converted and this will continue to work with the hybrid heat pump, or if the gas network is decommissioned they could be run completely on electricity.

viii. During the 2020s; increase heat pump uptake in homes not on the gas grid, with particular focus on those homes that would otherwise use high carbon fossil fuels.

ix. During the 2020s; all new homes should be future proofed for low carbon heating systems with appropriately sized radiator and low temperature compatible thermal stores. It is estimated that these measures could save householders between £1,500 and £5,500 compared to having to retrofit low carbon heat from scratch (Currie and Brown, 2019).

x. By 2025 at the latest no new homes should connect to the gas grid. Instead they should be designed to either use low-carbon heating systems such as heat pumps or be connected to low-carbon heat networks.

With biomass being discouraged, the technological constraints of decarbonising the gas grid, and the long-term policy and planning decisions needed for district heating schemes still being explored, it is expected that heat pumps may well become the most prevalent mainstream solution for supplying renewable heat to buildings in the immediate future. This increased uptake in the use of ASHPs and GSHPs has already been observed, and the technology is widely viewed as the most affordable and proven solution to low-carbon domestic heat, especially if the electricity consumed by their operation is also generated from renewable energy sources (Scottish Energy Statistics Hub, 2020e).

2.3.5 Achieving Balance

As the UK moves towards the net-zero emissions target there are considerable challenges to be addressed that will require a level of joined-up thinking and appreciation of the wider impacts decisions can have. The national electricity grid in particular will face difficulties maintaining rapid decarbonisation whilst responding to an unprecedented increase in demand from both the building and transport sectors. It is therefore more important than ever that architects take a holistic approach to reducing emissions and consider the wider impact of their design decisions, including the potential of a building to change and evolve in the future to achieve an even higher level of emission reductions.

In their recent cost and benefit analysis, Currie and Brown (2019) concluded that significant long-term carbon saving could be made by switching from natural gas to low-carbon heat in both domestic and non-domestic contexts. Their analysis found that the regulated operational carbon emissions of a home built in 2020 using a heat pump for space heating and hot water would, over a 60 year period, be 90% lower than the equivalent building heated with natural gas. Further they identified a significant carbon penalty and substantial cost implications in delaying adoption of low carbon heat technologies and retro-fitting them at a later date.

However they also recognised that combining a low-carbon heat source, such as an ASHP, with ultra-high fabric energy efficiency ultimately offered even greater overall benefits than either used alone (Currie and Brown, 2019). There are two main reasons for this. Firstly the reduction in heat loss that results from improving fabric energy efficiency to 15kWh/m².annum and operating a mechanical ventilation heat recovery (MVHR) system substantially reduce the building's annual and peak energy demands. This minimises the impact the building and the uptake of low-carbon heat has on the national electricity grid, and its ability to maintain both security of supply and continued decarbonisation. Secondly, there are both capital and operational cost savings at the building level because a much reduced energy demand can be satisfied with a smaller ASHP, a more compact heat distribution system and less radiators. Significantly analysis of these benefits determined that it would be more cost-effective to move rapidly to an ultra-high fabric energy efficiency combined with low-carbon heat, rather than take a more measured incremental approach to improving fabric energy efficiency (Currie and Brown, 2019).

The study further suggests that the adoption of low-carbon heat technologies such as ASHPs is cost-effective in the domestic arena from 2021; however Currie and Brown advise a more phased approach to manage transitional risks. The aim is therefore to have all new homes adopt an ultra-high level of fabric energy efficiency and low carbon heat from 2025 (CCC, 2019b, d; Currie and Brown, 2019). There is some caution required in transposing this cost analysis and timescale for adoption directly to the Scottish context. This is primarily because the modelling was based on a cavity wall construction rather than the timber frame construction methods more prevalent in Scotland. However, it is expected that an ultra-high fabric energy efficiency standard would be more readily achievable with a timber kit and potentially less expensive than achieving this level of fabric energy efficiency with a cavity wall construction. There are numerous examples of social and affordable housing built to Passivhaus standards using timber kit construction (Kinghorn Housing Association, 2010; Paul Heat Recovery Scotland, 2020a).

Rapid movement in tandem to both an ultra-high fabric energy efficiency and low-carbon heat is a very sensible course of action if this is sustainable in terms of grid capacity. Otherwise there may be a tendency among some developers to achieve their requisite CO₂ emission reductions mainly through the use of LZCGT and the positive gains made as a result of increased fabric energy efficiency might be lost with long-term negative consequences for both built and energy infrastructures.

2.3.6 Beyond Reducing Energy Demand

The Energy Performance of Buildings Directive (European Community Directive 2002 & European Community Directive 2010) introduced the term nearly zero-energy building (nZEB) (EC, 2018). Subsequently, a significant amount of research has been undertaken around the definitions of the term, the metrics used to account for energy and carbon emissions and the strategies needed for cost effective implementation of low carbon generating technologies in buildings, including Mussal and Voss (2012), Marszal and Heiselberg, (2010), Kibbert and Fard (2012), Hernandez and Kenny (2010) and Pless and Torcellini (2010). Various factors were highlighted in relation to energy balancing concepts including the indicators used, unit of balance (final/delivered energy; primary energy; exergy; energy costs or CO₂ emissions) and the type of energy used (operational energy; embodied energy and/or unregulated energy). They also showed that the boundaries for energy use need to be accounted for, including definitions for regulated energy, whether other end-uses not directly associated with the operation of the building, such as plug loads, are included and consideration given to how and the extent to which on-site LZCGT's offset both energy demand and emissions. They also show that understanding the different impacts and interactions between energy and carbon are important in designing appropriate integrated energy systems and that accounting for the 'quality' of the energy used is also important in accounting for emissions reductions. Time dependency between demand and generation is also highlighted as a significant barrier to further deployment of renewable technologies. In order to meet peak demand periods and reduce the impacts on an increasingly decarbonised grid, balancing energy supply and demand with storage (both short-term and seasonal) and controls will be needed in the future (Peacock et al., 2014).

2.4 Levels of Ambition

2.4.1 Passivhaus Standard

The aspirational Passivhaus standard is generally considered to set the international benchmark for achieving ultra-low energy building performance. Developed in Germany by Wolfgang Feist and Bo Adamson in 1988, the Passivhaus concept utilises knowledge of building physics to enable architects to systematically evaluate and fine tune building designs. Because of its clear scientific evaluation method and adoption of Mechanical Ventilation and Heat Recovery (MVHR) systems, Passivhaus is often wrongly perceived as an inherently technological and expensive way of building. In actuality its core principles are a holistic attitude to building design, a fabric first approach, excellent thermal detailing and exceptional care in construction (Cotterell and Dadeby, 2013).

Fundamental to a Passivhaus achieving an extremely low operational energy demand is a fabric first approach; combining high levels of insulation with an airtight and thermal bridge free construction. Sealing a building tight enough to effectively control heat loss necessitates a mechanical ventilation strategy to maintain indoor air quality during the heating season. The Passivhaus concept turns this necessity to its advantage by employing very low energy Mechanical Ventilation and Heat Recovery (MVHR) systems. Such systems typically employ a counter flow heat exchanger with an efficiency of between 80% and 93% to recover the heat from stale extract air and transfer it to the fresh supply air (Passive House Institute, 2020; Paul Heat Recovery Scotland, 2020b). In warmer weather this system can be simply bypassed and replaced with a natural ventilation strategy instead.

At this level of energy conservation it becomes possible to utilise incidental heat gains from passive solar, household activities, electronic equipment and the occupants themselves to help maintain an internal temperature of 20°C and effectively minimise the size of any heating system required (IBO, 2009; Cotterell and Dadeby, 2013; Paul Heat Recovery Scotland, 2020b). This represents a significant financial saving that partially compensates for the overall increase in cost due to increasing the efficiency of the building fabric. This combination of high fabric energy efficiency and heat recovery enables Passivhaus buildings to come close to the nearly zero-energy building definition without recourse to significant additional renewable energy input.

The Passive House Institute currently promotes three different aspirational standards: Passivhaus Classic, Passivhaus Plus and Passivhaus Premium (Table 2). These roughly equate to the definitions of an ultra-low energy building, a net zero energy building, and a plus energy building respectively (Paul Heat Recovery Scotland, 2020b). To attain any of these standards the annual space heat demand of the building required to provide an internal temperature of 20°C must be no more than 15kWh/m².annum; or, the specific heat load, i.e. the peak power needed to maintain 20°C internally when it is -10°C outside, must be no more than 10W/m² (Cotterell and Dadeby, 2013; Passive House Institute, 2016).

Table 2: Summary of Passivhaus Standards (Paul Heat Recovery Scotland, 2020b).The Renewable Primary Energy criteria replaced that of a maximum Primary Energy Demand in 2016. This value includes energy used for space heating, hot water, lighting, ventilation and all appliances and takes into consideration short-term and seasonal storage losses from renewable energy sources (Passipedia, 2017). These are not mandatory standards.

	Passivhaus Classic	Passivhaus Plus	Passivhaus Premium
Space Heat Demand	Maximum Annual Space Heat Demand of 15kWh/m2.annum . . . or . . . Maximum Space Heat Load of 10W/m2 Less than 0.6 air changes per hour @ 50 Pa Minimum 75% efficiency
Airtightness
MVHR
Renewable Primary Energy (PER)	Maximum 60kWh/m2.annum	Maximum 45kWh/m2.annum	Maximum 30kWh/m2.annum
Renewable Energy Generation	Not Required	Minimum 60kWh/m2.annum	Minimum 120kWh/m2.annum

How this level of fabric energy efficiency is achieved is at the discretion of the designer, however climatic conditions and the design of the building e.g. orientation, solar gain, form factor etc. will all contribute to determining what level of insulation is required. The form factor is essentially the ratio of the external surface area to the internal usable floor area. It is easier and cheaper to achieve a Passivhaus standard of construction with a more compact design (Cotterell and Dadeby, 2013). Table 3 outlines the impact of the form factor on typical u-values need to achieve the Passivhaus standard in the UK.

Table 3: How form factor affects U-value requirements (Cotterell and Dadeby, 2013).

Form Factor	Type of dwelling this might represent	U-value range of external envelope to achieve a space heat demand ≤ 15kWh/m2.annum in the UK
<2	Apartment block or terrace	0.15 W/m2K
2 -3	2 or 3 storey semi-detached or compact detached house	0.10 - 0.15 W/m2K
3-4	Less compact detached house or bungalow	0.10 W/m2K
>4	Very spread-out bungalow	0.05 - 0.10 W/m2K

2.4.2 UK and Scottish Aspirations

At the moment there is no mandatory maximum annual space heat demand set for either domestic or non-domestic buildings within the Scottish Building Standards (Scottish Government, 2019a; Scottish Government, 2019b). There are robust backstops set in relation to the performance of the building insulation envelope (Standard 6.2) and building services (Standards 6.3 – 6.7); and it is fully expected that these will have to be improved upon to enable a building to comply with its CO₂ emission reduction target (Standard 6.1). Different maximum area weighted u-values are set for domestic and non-domestic buildings, and these diverge further with respect to whether the works are new buildings, extensions, conversions or alterations. Building extensions have the most onerous requirements in this respect, to compensate for poorer levels of fabric energy efficiency in the existing building.

Data from a study in 2015, which considered the approved SAP data of 402 randomly selected new dwellings in Scotland, recorded an average annual space heat demand of 46.3kWh/m².annum, with actual values ranging from 13.7kWh/m².annum to 93.4kWh/m².annum (Appendix E; Onyango et al., 2016; Burford et al., 2019). All of these dwellings were designed between 2012 and 2014, were either under construction or completed at the time of the study, and met the minimum 30% reduction in CO₂ emissions (relative to the 2007 standard) legislated for in Scottish Building Standard 6.1 at that time. Energy standards for domestic buildings have since been revised so it is likely that the average annual space heat demand in new dwellings is now lower (Scottish Government, 2019a).

Aspirational sustainability standards have been set by the Scottish Government within Section 7 of the Scottish Building Standard (Table 4). These include at Silver/Silver Active Level, Aspect 2: a maximum annual space heat demand [SAP Box 99] of 40kWh/m².annum for houses and 30kWh/m².annum for flats and maisonettes. At Gold level this is improved to 30kWh/m².annum for houses and 20kWh/m².annum for flats and maisonettes (Scottish Government, 2019a). Attaining these levels is not mandatory.

Table 4: Summary of current aspirations for Scottish and UK standards compiled from the Scottish Building Standards Technical Handbook 2019: Domestic (Scottish Government 2019a), Reducing Emissions in Scotland: 2019 Progress Report to Parliament (Committee on Climate Change, 2019b) and UK housing: Fit for the future? (Committee on Climate Change, 2019d). These are not current mandatory standards, although the aspirations for 2025 are intended to be mandatory when adopted.

	Scottish Building Standards: 2019	Scottish Building Standards: 2019	Committee for Climate Change: 2019
New Domestic Buildings	Section 7 Silver/Silver Active	Section 7 Gold/Gold Active	UK Aspirations for 2025 at the latest
CO2 Emission Reduction (relative to 2007) (S7: Aspect 1)	45% (Mandatory)	60%	Unspecified
Annual Energy Demand for Space Heating (S7: Aspect 2)	Maximum Houses: 40kWh/m2.annum Flats/Maisonettes: 30kWh/m2.annum	Maximum Houses: 30kWh/m2.annum Flats/Maisonettes: 20kWh/m2.annum	Maximum All new homes: 15 - 20kWh/m2.annum
Space Cooling			All new homes should consider passive cooling measures to avoid overheating
Annual Energy Demand for Water Heating (S7: Aspect 3)	Minimum 5% from heat recovery or renewables	Minimum 50% from heat recovery or renewables
LZCGT (S7: Active)	Mandatory LZCGT contribution defined by individual planning authorities in local development plans. The use of LZCGT is promoted at building standards, but there is no mandatory requirement to use.		All new homes to be made ready for low carbon heating. No new homes to be connected to the gas grid by 2025 at latest. All new homes to use low carbon heat sources by 2025 at latest.
Whole Life Carbon Impact			Recommend shift to timber construction due to low embodied energy and high carbon storage potential
End of Life Strategy (S7: Aspect 8)		Design for Deconstruction

The Committee for Climate Change has also recently highlighted the aspirations that will need to be made concrete by 2025 at the latest to enable the UK achieve its net-zero emissions target (Table 4) (CCC, 2019b, p66; 2019d, pp 14-15). They counsel that all new homes in the UK should be designed to deliver ultra-high levels of energy efficiency as soon as possible, and by 2025 at the latest. This proposed ultra-high level of energy efficiency was considered consistent with an annual space heat demand of 15 to 20kWh/m².annum (CCC, 2019d, p14). They also recommend that all new homes be made suitable for low carbon heat now; and by 2025 at the latest no new homes should connect to the gas grid but should instead use low-carbon heating systems such as heat pumps and low-carbon heat networks. There are also recommendations that there should be a refocussing of efforts on the whole-life carbon impact of new homes. In particular they advise a shift towards timber frame construction because of its lower embodied energy and ability to act as a long-term sequestrated carbon store. This is, of course, already the standard construction method in Scotland.

2.5 Effective Policy Design

2.5.1 Overview

There is a considerable body of academic literature devoted to GHG emission reduction and renewable energy policies. However most is based on empirical work undertaken across the globe in contexts that are climatologically, environmentally, politically, socially and economically diverse. These contextual differences along with divergences in aspirations, concepts and calculation methodologies relating to nearly zero-energy buildings effectively hamper accurate benchmarking of the performance of these different approaches and largely constrain direct comparison and cross-context learning (Pan and Li, 2016).

There is a general consensus that reducing GHG emissions from buildings is best tackled by taking a multifaceted approach (Urge-Vorsatz et al., 2013; Beradi, 2016; Grove-Smith et al., 2018). However, improving building energy efficiency is repeatedly highlighted as the most significant and cost effect means of reducing energy demand and GHG emissions, and ultimately protecting the environment. This finding is supported by numerous and comprehensive reviews of building energy consumption data from the UK, USA, EU and China (Xing et al., 2011; Annunziata et al., 2013; Urge-Vorsatz et al., 2013; Pan, 2014; Cole and Fedoruk, 2015; Beradi, 2016; Grove-Smith et al., 2018). A full analysis of the academic literature is contained in Appendix D.

2.5.2 Design and Application of Robust Energy Policies

Empirical analysis of policy instruments in the building sector clearly shows that governmental intervention is fundamental in reducing GHG emissions from buildings (Ürge-Vorsatz et al., 2008; Boza-Kiss et al. 2013; Levinson, 2014; Lemprière, 2016; Gürtler et al., 2019; Schwarz et al., 2020). However, it is also true that in many countries these changes in building regulations are often subject to debate and review as conflicting goals become evident between minimising regulatory and administrative burden on citizens and businesses, and addressing socio-economic and environmental concerns (Gürtler et al., 2019; Schwarz et al., 2020).

Gürtler et al. (2019) sought to understand the mechanisms, factors and actors that led to certain government policies succeeding whilst others ultimately collapsed; by considering the dismantling of renewable energy policies in Spain and the Czech Republic. Policy design was obviously a major factor in the robustness of a policy. The outcome was also determined by other wider societal factors e.g. interplay between policy design, the political economy of the policy field, macro level external factors, and institutional constraints and opportunities that could either reinforce or weaken a policy (Figure 3). Their preliminary findings determined that with some forethought many of these factors could be effectively managed and mitigated for. The primary lessons learnt were to:

i. Recognise fiscal feedback can strongly influence policy durability:

It is important that the societal cost of the policy is effectively controlled. Costs incurred must not be seen as damaging by stakeholders, politicians or the general public and should be fairly distributed. The perception that the policy provides excess benefits to a small group of stakeholders, or equally adversely affects others, should be avoided.

ii. Develop an explicit strategy for managing the political economy:

This entails gaining an in-depth understanding of the political economy of the field and addressing the concerns of the primary stakeholders with either policy changes or other interventions to mitigate any transitional periods.

iii. Maintain ambition and the ability to adapt:

Policy collapse can often occur prematurely if it is perceived that targets and objectives have been met. If further improvements are possible and desirable, there is a need in this context to keep momentum going through the use of adaptive frameworks which can respond effectively to innovation and change, and prevent stagnation of ambition.

In another recent study, Schwarz et al. (2020) identified five case studies where innovative approaches to building energy policy design had been taken by Denmark, France, Sweden, Switzerland and the UK. By exploring the effectiveness and challenges experienced in implementing these energy policies, they identified six policy design principles:

i. Keep additional burdens for building owners light.

Building energy policy should only require cost-effective measures that are economically beneficial to the consumer.

ii. Create long-term regulatory certainty.

This allows time for forward planning, investment and innovation to develop whether industrial or architectural. There is however a need to build in a degree of flexibility to enable effective response to developing knowledge, opinion, innovations and societal expectations.

iii. Beware technologically specific requirements.

It is recommended that there are multiple technological options available to choose from, for the most appropriate and cost-effective technology for any given context.

iv. Anticipate the impact of new regulations on small actors.

The cost impact of increasingly complex environmental legislation may be much more onerous for small firms and planning authorities, than large firms because of economies of scale. This should be borne in mind and expensive and time consuming compliance and evidencing procedures reduced as much as possible. Necessary information and means of evidencing compliance should be made free and publically available.

v. Promote knowledge of innovative policy designs.

Ensure that all stakeholders have sufficient knowledge about new policies well in advance of implementation. This can be achieved by pre-announcing upcoming changes to legislation, conducting pilots, building on voluntary schemes or learning from front-runner legislation enacted elsewhere.

vi. Integrate building energy policy in the local context.

It is important to adapt policies to the local context by leveraging existing energy infrastructures and locally available renewable energy resources.