Planning policy - section 3F: research

Executive Summary

Section 3F Policy

Introduction

This report was commissioned to help develop a Scotland wide Section 3F planning policy, by proposing reasonable levels of CO₂ (Carbon dioxide) emissions reduction that can be expected from use of low and zero carbon generating technologies (LZCGTs) in new buildings. The research also draws attention to methods by which planning officers can ascertain that the reductions have been met. Section 3F of the Town and Country Planning (Scotland) Act 1997, as amended through Section 72 of the Climate Change (Scotland) Act 2009 states that:

'A planning authority, in any local development plan prepared by them, must include policies requiring all developments in the local development plan area to be designed so as to ensure that all new buildings avoid a specified and rising proportion of the projected greenhouse gas emissions from their use, calculated on the basis of the approved design and plans for the specific development, through the installation and operation of low and zero carbon generating technologies.'

(Scottish Parliament, 2019b).

As a consequence, planning authorities across Scotland have had relative autonomy in determining the contribution LZCGT should make to the CO₂ emission reductions of new buildings. This has led to duplication of effort in determining appropriate policies; inconsistences in terms of the LZCGT contribution sought, compliance procedures and calculation methodologies; and a general lack of clarity for all stakeholders. In response, the Scottish Government is using the preparation of the next National Planning Framework to further explore how the legislative requirements could be met, with a particular focus on the level of emission savings from the use of LZCGTs.

Objectives

The objectives of this study were to support the Scottish Government's aim in this respect in three ways:

i. Propose a methodology to identify the level of CO₂ emission savings that would be reasonable to expect from the use of LZCGT in new buildings.

ii. Recommend the proportion of CO₂ emission savings which could be reasonably sought as a result of the use of LZCGT in new buildings over the next 10 year period.

iii. Propose a calculation methodology for use by development management officers to understand whether the specified LZCGT contribution has been met.

Methodology

The research was primarily desk-based. Literature was reviewed relating to current best practice approaches to CO₂ emission reduction in buildings, the principles underpinning robust energy policy design, the regulatory framework within which Section 3F policy operates, and the calculation methods embedded in the Standard Assessment Procedure (SAP) used to calculate CO₂ emission from new buildings. A survey was undertaken to learn from the experiences planning authorities have gained as a result of administrating current Section 3F policies (Appendix A). The aim was to benchmark current policy and procedures, and reveal where practical issues or concerns were being raised.

Literature Review

The Climate Change (Emissions Reduction Targets) (Scotland) Act 2019, amended the Climate Change (Scotland) Act 2009, advancing the timeframe for reducing GHG (Greenhouse Gas) emissions in Scotland to net-zero by 2045 at the latest. Interim targets for reductions of at least 56% by 2020, 75% by 2030 and 90% by 2040 were also set (Scottish Parliament, 2019a). Further, the revised Climate Change Plan sets specific targets requiring 35% of the heating demand in new domestic buildings to be provided by low-carbon technologies by 2032. In non-domestic buildings this target will be 70% (Scottish Government, 2018a).

Decarbonising heat is seen as the single biggest challenge in decarbonising Scottish buildings. New targets introduced in 2019 legislate for ultra-energy efficient dwellings from 2025 which utilise low-carbon heating thereby reducing the reliance on the gas grid. Further, impending restrictions limiting the use of biomass expected in the near future means that heat pumps are widely viewed as the most affordable and proven immediate solution to domestic low-carbon heating. With the electricity grid currently at near-capacity, grid constraints are a major barrier in moving to the electrification of building heating. Overcoming intermittency issues and reducing peak demands, which are more likely in moving to heat pump technology, will be the critical limiting factors in protecting the security of the electricity supply. Energy balancing generating technologies at the building may be needed to offset all or a significant proportion of the regulated power and heat requirements. This still assumes that the grid has the capacity to supply peak demand and it does not take into account intermittency inherent in the generation of renewable energy, which will need additional considerations such as energy storage to overcome.

A holistic approach is generally considered the best long-term strategy to reduce CO₂ emissions in buildings. This approach could be characterised as three stages:

i. Reduce energy demand

ii. Increase energy efficiency

iii. Increase use of renewable energy to cover remaining energy demand.

A substantial reduction in energy demand is crucial to this strategy. Without it the ability to meet the remaining demand through the use of renewables and LZCGT is diminished and less cost effective.

Prioritising a fabric first approach is advised in the majority of the literature. This approach has numerous benefits. Increased fabric energy efficiency reduces energy demand and therefore directly reduces CO₂ emissions. Reducing energy demand protects national energy security by reducing the need for extra generating capacity in the network. This is of particular importance when bearing in mind expected growth in electrical needs due to proposed switch to electrical vehicles and the anticipated increase in electrical demand from heat pumps. Getting the fabric right from the outset effectively locks in carbon savings for the lifetime of the building, whereas the benefits of LZCGT only last the lifetime of the equipment which is usually only 15 to 20 years. It is also more difficult and expensive to upgrade fabric energy efficiency at a later date than at the construction stage. Increased fabric energy efficiency also reduces energy poverty and has positive effects on the comfort, health and well-being of occupants.

At very high fabric energy efficiency standards e.g. Passivhaus, the demand on the heating system is significantly reduced and the cost savings made help balance out the cost of improving the fabric. However, there is a balance to be made between reduced operational energy use and the increased embodied energy of the construction materials if going beyond this point.

In Scotland, limiting energy consumption and CO₂ emissions from new buildings is primarily legislated for through Section 6 of the Scottish Building Standards. Section 6 takes a holistic whole building approach; allowing architects to meet the emission reduction targets calculated through SAP/SBEM (Simplified Building Energy Model) by any means they deem suitable, subject to meeting robust fabric energy efficiency and equipment efficiency backstops. Under the current building standards the use of LZCGT is not mandatory. Conversely, Section 3F Planning Policy is a single-issue policy which makes the use of LZCGT mandatory in new buildings. Section 3F policy does not seek to increase CO₂ emission reductions beyond that set by Scottish Building Standard 6.1; it simply defines the proportion of those emission reductions that should be achieved through the deployment of LZCGT.

Section 3F Survey

It is expected that the development of a Scotland-wide Section 3F policy will improve policy awareness and provide greater clarity and consistency for design practitioners, which in turn should improve the standard of compliance information submitted to Planning. Greater clarity in terms policy aims, LZCGT contribution target, evidence requirements and calculation methodology, as well as guidance on implementation procedures and enforcement is essential moving forward. The current standard of compliance evidence submitted to planning authorities is extremely variable. The main issue for both implementation and enforcement is attempting to apply a policy at the planning stage, when the information that is required to confirm compliance with the specified LZCGT contribution target is typically not available until later in the design process. The use of suspensive conditions to enable detailed technical information to be submitted later in the design process, prior to works commencing on site, is widespread, but not without difficulties. Almost half of survey respondents had concerns about the strength of suspensive conditions and the subsequent ability to enforce compliance.

In the long-term there is a need to address the underlying conflict between Planning and Building Standards over the mandatory use of LZCGT, convey a clear and consistent message, and generally develop collaborative working practices on the issue of climate change and CO₂ emissions reduction. It is beyond the legal remit of Building Standard officers to play an active role in enforcing planning policy, and they will not delay granting building warrant consent or issuing a completion certificate on the basis that an application does not comply with a planning condition (Scottish Government, 2019e).

The majority of survey respondents felt that quantitatively assessing the contribution of LZCGT to CO₂ emissions reduction would be an issue better dealt with and enforced through Building Standards. It was suggested that a new mandatory standard within the Scottish Building Standards that meets the minimum LZCGT contribution target set by Section 3F policy could remove many of the existing difficulties currently encountered by planning officers, and give Building Standards an active role in enforcement. This would not negate the major role that Planning would still play in prioritising, discussing, advising and influencing action on climate change, the reduction of CO₂ emissions and Section 3F policy at an early stage in the design process. Planning has a large sphere of influence and the potential to reduce CO₂ emission in many different arenas beyond the single issue confines of Section 3F policy. Regular feedback on outcomes, to judge successes and failures within the system, and how collaboration between planning and building standards officers could be improved, would benefit the process.

Proposals

In response to the brief we have included two separate proposals:

• Proposal 1: Is a minimum LZCGT contribution standard, which simply fulfils the objectives of the brief as stated.
• Proposal 2: Is a whole building approach, which re-envisions Section 3F policy in line with the more holistic approach taken by Building Standards. This is as a result of the researchers' own further reflection while undertaking the study. Focussed on the domestic sector and centred on the idea of a maximum acceptable annual energy demand per occupant; it seeks to promote a more equitable use of resources, address fundamental design issues such as dwelling scale, prioritise fabric energy efficiency and promote the use of LZCGT.

Proposal 1: A minimum LZCGT Contribution Standard

Proposed Methodology to identify a reasonable level of LZCGT contribution to CO₂ emission reduction

The proposed methodology is pragmatic in approach, envisioning what would be an appropriate LZCGT contribution to the annual energy demand in new domestic buildings under different CO₂ emission reduction standards. The purpose is to identify a reasonable level of LZCGT contribution to CO₂ emission reduction in new buildings. It does this by gauging the practical impact on annual energy demand of utilising LZCGT in new buildings to either replace a proportion of the annual energy demand or generate electricity to offset that demand, and what real-world practical limitations might be encountered in doing so.

The data used in these deliberations was based on the predicted energy demand for dwellings ranging in size from 25m² to 300m² calculated using formulae prescribed in the Standard Assessment Procedure (SAP) 2012 (BRE, 2014). Three different scenarios were developed representing three different fabric energy efficiency standards: 45kWh/m².annum, 30kWh/m².annum and 15kWh/m².annum. These scenarios were developed to provide a reasonable approximation of past, present/near future and future fabric energy efficiency contexts.

Modelling was based on the domestic sector for several reasons:

i. Domestic buildings are the most frequent building type encountered by planning authorities.

ii. The domestic sector consumes a much larger proportion of energy for space heating, hot water and lighting than other sectors.

iii. It is vital that Section 3F policy does not adversely impact on the ability to deliver essential domestic infrastructure such as affordable and social housing in a cost effective way.

iv. Non-domestic buildings have fairly diverse energy consumption patterns contingent to their functional needs. It was therefore considered more reliable to determine a reasonable LZCGT contribution for the domestic sector and extrapolate to the non-domestic, rather than vice versa.

This judgement as to what would be a reasonable LZCGT contribution to annual energy demand in new buildings was made with respect to the following criteria:

i. It should be a reasonable minimum expectation, in respect to the overall level of CO₂ emission reduction new buildings are expected to achieve due to the changing regulatory climate.

ii. It should be readily achievable by all buildings whether in an urban or rural context.

iii. It should be low enough not to undermine or dis-incentivise a fabric first approach or other innovative passive design responses to CO₂ emission reduction.

iv. It should not be too onerous in terms of cost, and should offer long-term value for money for stakeholders.

v. It should not restrict the architect to only one viable option in choice of LZCGT, either directly or indirectly.

vi. It should not interfere with the ability to deliver wider sociological goals or essential infrastructure. In this respect the delivery of affordable and social housing was defined as a significant parameter. Consequently, final assessments were focussed on the impact the LZCGT contribution level would have on this critical context, specifically dwellings ranging in size from 45m² to 100 m².

Taking these factors into consideration the level of LZCGT contribution to CO₂ emission reduction that could be reasonably sought by Section 3F policy must by necessity be a minimum standard rather than an aspirational one.

Recommendations

Having determined what would be a reasonable LZCGT contribution as a percentage of annual energy demand under different CO₂ emission reduction standards, it was necessary to express this in terms of CO₂ emissions. This refers to levels of CO₂ emission saving which could be reasonably sought as a result of the use of LZCGT in new buildings over the next 10 year period. Three alternative ways of defining LZCGT contribution relative to CO₂ emissions were identified in current Section 3F policy (Scottish Government, 2019b). We designated these metrics, A%, C% and E%:

A%	An absolute percentage CO2 emission reduction relative to the 2007 baseline established by Scottish Building Standard 6.1.
C%	A percentage of the percentage CO2 emission reduction sought through Scottish Building Standard 6.1 relative to the 2007 baseline.
E%	An avoidance of a percentage of the building projected CO2 emissions as calculated by SAP/SBEM (Simplified Building Energy Model).

The final metric (E%) most closely aligns to the definition included in Section 3F policy, and equates reasonably well, although not exactly, to the LZCGT contribution defined as a percentage of annual energy demand. From a practical standpoint it is the most useful to architects and developers because it relates directly to real world variables they can understand and manipulate in the design process.

However, on balance, we recommend that in Section 3F policy the minimum LZCGT contribution be defined in terms of a percentage of the percentage CO₂ emission reduction sought through Scottish Building Standard 6.1 for several reasons:

i. Linking Section 3F policy directly to Building Standard 6.1 avoids potential conflict.

ii. It simplifies Section 3F policy, by allowing the LZCGT contribution to be defined as a constant and perpetual percentage that will automatically deliver increases in real terms with every improvement of Standard 6.1 (Table 1).

iii. It provides regulatory certainty going forward.

iv. It ensures changes that occur in Building Standards 6.1 are reflected immediately, proportionately and automatically in Planning.

v. It allows differences in the CO₂ emission reduction sought for domestic and non-domestic buildings at building standards, to be simply and automatically reflected in the LZCGT contribution sought at Planning.

It is vital that it is understood that any attempt to increase the level of LZCGT contribution either disproportionately or at more frequent intervals than the changes to overall CO₂ emission reduction sought by Building Standard 6.1, will undermine the fabric first approach. It should therefore be avoided. However this is a minimum standard and does not preclude designers of new buildings from deciding not to take the recommended fabric first approach and using a higher percentage of LZCGT to meet their Target Emission Rate (TER) if they wish to do so.

We recommend that the LZCGT contribution to CO₂ emission reductions be defined as a constant and perpetual 12% of the percentage CO₂ emission reduction sought through Scottish Building Standard 6.1.

R%	A %	C %	E %
0% CO2 Reduction Standard	0 %	12.0 %	0 %
30% CO2 Reduction Standard	3.6 %	12.0 %	4.9 %
45% CO2 Reduction Standard	5.4 %	12.0 %	8.9 %
60% CO2 Reduction Standard	7.2 %	12.0 %	15.3 %
75% CO2 Reduction Standard	9.0 %	12.0 %	26.5 %
90% CO2 Reduction Standard	10.8 %	12.0 %	51.9 %
100% CO2 Reduction Standard	12.0 %	12.0 %	100 %

Table 1: The same minimum LZCGT Contribution target calculated relative to each metric under different Standard 6.1 CO₂ emission reduction contexts.

It is expected that once the carbon factors used in the SAP/SBEM methodology are updated with the introduction of SAP10, that there will be a dramatic increase in the use of heat pumps. We would suggest that the CO₂ emission standard and building insulation envelope backstops (Standards 6.1 and 6.2) need to be improved accordingly at this stage. Otherwise there may be a tendency among developers to achieve their CO₂ emission reduction targets 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.

Proposed Calculation Methodology

Not all LZCGT have zero carbon emissions. Therefore the simplest way to accurately calculate if the specified LZCGT contribution has been met is to run two separate SAP/SBEM calculations; one for the building as designed with the proposed LZCGT and another with the proposed LZCGT removed and replaced with pre-defined conventional systems. We would recommend that the presumption of what replaces the LZCGT in this second SAP/SBEM calculation is consistent for all buildings; although the appropriateness of this needs further consideration by Building Standards. The CO₂ emission rates generated by these two SAP/SBEM calculations are then substituted into a formula to calculate the LZCGT contribution. If the value calculated is greater than or equal to the relevant figure given in Table 1 the proposed building has complied with Section 3F requirements.

The formula to calculate LZCGT contribution defined as an absolute percentage CO₂ emission reduction relative to the 2007 baseline is given by:

The formula to calculate the LZCGT contribution defined as a percentage of the percentage CO₂ emission reduction sought by Scottish Building Standard 6.1 is given by:

The formula to calculate the LZCGT contribution defined as an avoidance of a percentage of projected CO₂ emissions as calculated by SAP/SBEM:

Where:

DER = Dwelling Emission Rate
DERNT = Dwelling Emission Rate calculated with no LZCGT
TER = Target Emission Rate
R% = Statutory required CO₂ emission reduction sought by Scottish Building Standard 6.1 defined as a percentage relative to the 2007 baseline.

Proposal 2: A Whole Building Approach

Overview

This proposal takes a whole building approach to CO₂ emission reduction and diverges significantly from current Section 3F Policy, which it reinvents in a way that plays to the strengths and skillsets of Planning, whilst complementing and aligning constructively with the holistic approach taken by Building Standards. Focussed on the domestic sector; the proposal centres on the idea of limiting annual energy demand (AED) in new dwellings to an acceptable per capita level; and through this mechanism it aims to leverage better design solutions, prioritise fabric energy efficiency, promote the use of LZCGT and address fundamental issues not tackled by the current system.

This acceptable annual energy demand (AAED) will be defined on a per capita basis, calculated with respect to the predicted occupancy and annual energy demand (AED) of a modest-sized energy-efficient dwelling. A modest-sized dwelling has been defined as between 45m² and 100m² (Appendix E). This measure should allow the target rate to be set at an ambitious but achievable level, whilst ensuring that it does not impact adversely on the ability to deliver essential domestic infrastructure such as affordable housing.

The objective of this mechanism is to:

i. Realise in practice the recommended 3-step holistic approach to reducing CO₂ emission from buildings:

• Reduce energy demand
• Increase efficiency of energy use
• Increase the use of zero-carbon renewable energy

ii. Focus on those issues that ideally need to be addressed early in the design process and that planning can positively influence.

iii. Recognise that architectural design plays a significant role in reducing energy demand, and incentivise good design, passive design responses and innovative approaches.

iv. Prioritise fabric energy efficiency as a means of reducing energy demand.

v. Promote the use of high quality zero-carbon renewable energy sources (LZCGT).

vi. Address the finite nature of resources, issues of personal choice and responsibility, and determine a fair and equitable share of resources for everyone.

vii. Directly address the energy and material consumption issues related to scale and excessive per capita heated living space in large domestic buildings (Burford et al., 2019).

Compliance with the proposal will be allowed through any combination of design, fabric energy efficiency, equipment efficiency or LZCGT. Applicants will be actively encouraged to meet the acceptable annual energy demand (AAED) calculated for their proposed dwelling through good design and fabric energy efficiency measures alone, if that is feasible and cost effective. However if a dwelling does not manage to achieve this, then all remaining energy demand in excess of the acceptable level must be met by zero-carbon renewable energy sources.

As the focus of the proposal is on reducing the annual energy demand of dwellings and increasing the use of zero-carbon renewable energy, it was decided that the metrics used should reflect this. The metric used throughout will therefore be kWh/annum. There are several reasons for this:

i. It keeps the focus on energy, and emphasises the need to first and foremost reduce energy demand, both to ensure long-term energy security and reduce CO₂ emissions.

ii. It is a tangible and easy to comprehend metric with real world meaning for all stakeholders which allows the impact of design changes to be easily quantified and understood.

iii. It allows the contribution of LZCGT to the annual energy demand to be clearly and easily quantified.

iv. It is the base metric used in SAP calculations, and data extracted from this document will be expressed in kWh/annum

v. It is the obvious metric to link LZCGT contribution, annual energy demand, and regional or national energy networks. It is therefore much more useful in ongoing reporting and the development of future regional or national energy strategy than a carbon metric.

vi. By avoiding a carbon metric it circumvents any potential conflict with Scottish Building Standard 6.1.

Compliance Target

The acceptable annual energy demand per capita (AAED/Capita) for new dwellings was determined using the same data stream as Proposal 1. This involved modelling the annual energy demand of dwellings ranging in size from 25m² to 300m² using formula prescribed in SAP 2012 (BRE, 2014). To effectively assess how the target level might potentially shift over time, two different scenarios were developed to represent evolving fabric energy efficiency standards. These were based on space heat demands of 30kWh/m².annum and 15kWh/m².annum respectively to represent present/near future (2020-2021) and future (2024-2050) contexts.

As there are issues with excess per capita energy consumption in large dwellings because of their inherent scale and relatively low average occupancy rates (BRE, 2008); the AAED/Capita level was established with respect to the predicted annual energy demand of modest-sized dwellings between 45m² and 100m². This acceptable level will apply to all dwellings regardless of size, and it is recognised that it will be potentially more challenging for large dwellings as a result. However with considered design it is still readily achievable (Appendix C: Worked Examples) It should also be remembered that it is not the intention of this proposal that dwellings should meet the AAED/Capita target purely by dint of increased fabric energy efficiency. It is accepted in the compliance methodology that some of the annual energy demand can be effectively offset through the use of zero-carbon energy sources. By whatever means it is achieved, reducing the per capita annual energy demand of large dwellings to bring them in line with more modest dwellings, could deliver truly substantial CO₂ emission reductions in this sector (Appendix E).

We recommend AAED/Capita targets levels are set at:

2021 AAED/Capita = 1910 kWh/annum
2024 AAED/Capita = 1500 kWh/annum

As the country evolves towards 2050 and net-zero carbon buildings, it is envisaged that the AAED/Capita would be progressively reduced until it reaches zero. At this point all remaining regulated energy demands from new dwellings would have to be met by zero-carbon renewable energy sources.

Documenting Compliance

Compliance is basically determined by comparing three values calculated for the proposed dwelling:

Acceptable Annual Energy Demand
AAED

Annual Energy Demand
AED

Zero-Carbon Adjusted Annual Energy Demand
ZCAED

Compliance is achieved if either of the following hold true:

Compliance Method 1: (With or Without LZCGT)
AED ≤ AAED

Compliance Method 2: (With LZCGT)
ZCAED ≤ AAED

The compliance documentation was designed with the objective of making the entire process as easy as possible for all stakeholders, whilst taking the opportunity to collect useful data for research and future energy planning purposes. It comprises of a standardised Excel spreadsheet, split into two sections; Section 1 is to be completed for dwellings that have individual energy systems and micro-CHP (Appendix C: Figures C.3 and C.4), Section 2 for those with community heating systems (Appendix C: Figures C.5 and C.6). Each Section is sub-divided into a Data Input worksheet and a Compliance Calculation worksheet.

To use the spreadsheet, the applicant simply extracts the relevant data from the SAP document submitted to Building Standards for the proposed dwelling and inputs this into the appropriate Data Input worksheet. There is no need to have knowledge of the workings of SAP calculations to complete the spreadsheet as all required data is referenced by its SAP box number. The whole process should take no more than 10 minutes. Excel then performs all the necessary calculations automatically and the results are displayed on the Compliance Calculation worksheet.

Through the use of this spreadsheet the compliance procedure is simplified as much as possible. The Compliance Calculation worksheet provides both a clear statement of policy compliance/non-compliance and a quantified breakdown of the contribution of individual energy systems, fuels and LZCGT. These are characterised as zero-carbon, low-carbon, grid electricity, bio-carbon or fossil fuel, and colour coded to indicate preferable choices. To incentivise best practice, only zero-carbon energy sources are used to calculate the zero-carbon adjusted energy demand (ZCAED).

The compliance procedure is quite flexible and there are several ways that a designer can bring a non-compliant building into compliance, either by reducing the annual energy demand (i. – iv.) or employing additional zero-carbon renewable energy systems (iv. – vii.). Used alongside SAP, the compliance spreadsheet can be exploited as a design tool for architects, developers and planners to objectively explore these different options. These measures might include:

i. Revising the building design by considering scale, built form, solar orientation, and other passive design measures to reduce overall energy demand.

ii. Increasing fabric energy efficiency.

iii. Increasing air tightness and employing MVHR.

iv. Considering solar thermal or waste water heat recovery (WWHR).

v. Considering zero-carbon electricity generation such as PV, wind, water etc.

vi. Considering zero-carbon heat generation including all types of heat pumps. Be aware however that in calculating the zero-carbon contribution, the electrical input will be subtracted from the output.

vii. Considering a community heating scheme. Typically numerous different energy sources may be employed within a single district heating scheme, some of which would not be feasible at the individual building scale. In the compliance calculation methodology each of these will be considered proportionally and on their individual merits. Scaled zero-carbon renewable energy sources might include PV, wind, water, tidal or geothermal energy, waste heat recovery from power stations, or waste heat recovery from industrial or agricultural processes.

Conclusion

This report has been informed by relevant considerations from academic and grey literature in relation to reducing CO₂ emissions from buildings, and the issues raised by planning officers in local authorities across Scotland who are administrating current Section 3F policies. As a result, two distinct proposals that might be appropriate for the Scottish Government to consider at this juncture, are developed and presented. However, the strengths and weaknesses of each proposal, and the limitations of some of the assumptions made in formulating these approaches, target levels, and workflows for demonstrating compliance, are worth highlighting.

Both proposals took an essentially pragmatic approach to determining target levels, guided by relevant Scottish government policy pronouncements and aspirations; and deliberations were based on the predicted energy demand of dwellings ranging in size from 25m² to 300m² calculated using formulae prescribed in the Standard Assessment Procedure SAP 2012 (BRE, 2014). Particular attention was paid to dwellings between 45m² and 100m² as it was felt this size range would include the majority of social and affordable housing.

Three scenarios were developed to provide a better appreciation of how improvements in fabric energy efficiency could potentially impact on annual energy demand and the viability of certain LZCGT solutions. In the absence of a firm timetable of commitment to improving CO₂ emission reduction in new buildings, a future scenario based on a space heat demand of 15kWh/m².annum was developed. This is in line with the recommendation by the Committee on Climate Change that by 2025, at the latest, all new buildings should be built to an ultra-high fabric energy efficiency standard commensurate with a space heat demand of 15 – 20 kWh/m².annum and be designed to use low carbon heat (CCC, 2019b, p66; CCC, 2019d, pp 14-15).

Modelling was based on domestic buildings because these are the most frequent building type encountered by planning authorities; they consume a much larger proportion of energy for space heating, hot water and lighting than other sectors; and avoiding any unintended impact on the ability to deliver affordable housing was considered of paramount importance (BEIS, 2019a).

Proposal 1 satisfies the research objectives as stated in the brief relative to Section 3F Policy as enacted in current legislation. It acknowledges that other factors also contribute to reducing emissions from buildings, and defines a realistic minimum LZCGT contribution to CO₂ emission reduction in new buildings that could be sought by Section 3F policy without undermining the viability of a fabric first approach or the development of innovative passive design solutions. This approach does not preclude architects and developers from using a higher proportion of LZCGT to meet their Target Emission Rate (TER) if they so desire.

Although target levels were determined with respect to empirical quantitative data, the methodology used to determine what would be 'reasonable' under different CO₂ emission reduction standards was essentially a qualitative judgement. The levels calculated by this method were subsequently evaluated with respect to interim targets and aspirations set by the Scottish Government (Scottish Government, 2018a, pp. 87-89; CCC, 2019b, p66; Scottish Parliament, 2019a), and found to be in general accord.

Having determined what would be a reasonable LZCGT contribution as a percentage of annual energy demand under different emission reduction standards, it was necessary to express this in terms of a percentage CO₂ emission reduction to comply with the requirements of Section 3F policy. Although three alternative ways of defining LZCGT contribution relative to CO₂ emissions were identified in current Section 3F policies; presenting it as "A percentage of the percentage CO₂ emission reduction sought through Scottish Building Standard 6.1 relative to the 2007 baseline" was most appropriate.

It effectively links Section 3F policy directly to whatever is the CO₂ emission reduction required by the current Scottish Building Standard 6.1. However, we note that this metric is problematic from a practical design standpoint. Consequently there is a need to ensure that stakeholders can understand the practical implications of this metric in terms of the LZCGT contribution to annual energy demand that would be required to meet this target under different emission reduction standards. This could be achieved through reference to Figure 8, Table 9 and/or the type of graphical data developed for each scenario (Appendix B).

Showing compliance is relatively straightforward and a standard excel spreadsheet has been developed for this purpose (Appendix C: Proposal 1). The compliance calculation utilizes the emissions rates (DER and TER) calculated for the dwelling by the SAP methodology. However it also requires a second SAP calculation to be conducted to determine the dwelling emission rate with the LZCGT removed and replaced with pre-defined conventional system (DERNT). What these replacement systems will consist of needs to be clearly defined. The final compliance calculation is then a simple matter of substituting these factors and the required emission reduction standard (R%) into the formula and if the result is greater than or equal to the target percentage the building is in compliance. This has been calculated as 12% for both domestic and non-domestic buildings under all emission reduction standards. This level of LZCGT contribution is in general accord with interim targets set by the Scottish Government in order to achieve net-zero emissions by 2045, without onerous burdens to the public and without being too high as to undermine the fabric first approach.

Proposal 2 takes a whole building approach to CO₂ emission reduction which diverges significantly from the enacted Section 3F policy and would therefore require new legislation. It was not part of the brief but we arrived at it based on our own insights from undertaking the study.

This proposal re-invents policy in a way that focuses on the strengths, skillsets and wider objectives of Planning, whilst complementing the whole building approach taken by Building Standards. It concentrates solely on domestic buildings, and centres on the idea of limiting annual energy demand (AED) in new dwellings to an acceptable per capita level. Through this mechanism, it aims to leverage better design solutions, prioritise fabric energy efficiency, promote the use of LZCGT, and address fundamental issues not tackled by the current system.

Policy compliance will be established by completing a simple standardised spreadsheet with data taken directly from the building's SAP document. Applicants will be actively encouraged to meet the acceptable annual energy demand (AAED) calculated for their proposed building through good design and fabric energy efficiency measures alone, if that is feasible and cost effective. However, if a dwelling does not manage to achieve this, then all remaining energy demand in excess of the acceptable level must be met by zero-carbon renewable energy sources.

The methodology used to determine an acceptable annual energy demand per capita (AAED/Capita) is based on a simple calculation; with the judgement of what is reasonable primarily embedded in the space heat demand deemed appropriate to the timeframe in question and the range of dwelling sizes taken under consideration. It should be noted that if either of these variables is changed the resultant AAED/Capita would be substantially different (Appendix E)

The AAED/Capita was established with respect to the predicted annual energy demand (AED) and assumed occupancy (N) of modest-sized dwellings of between 45m² and 100m². This allows the target rate to be set at an ambitious but achievable level, whilst ensuring that it does not impact adversely on the ability to deliver essential domestic infrastructure such as affordable housing. The target AAED/Capita will apply to all dwellings regardless of size. It is recognised that it will be potentially more challenging for large dwellings, but it is still readily achievable (Appendix C).

As the country evolves towards 2045 and net-zero carbon buildings, it is envisaged that that the AAED/Capita could be progressively reduced until it reaches zero. At this point any remaining regulated energy demands in new dwellings would have to be met by zero-carbon renewable energy sources.

The proposal takes a more broad brush approach to CO2 emission reduction certain in the knowledge that reducing annual energy demand and/or replacing a proportion of that demand with zero-carbon renewable energy sources will inevitably have a positive impact. It does not apply carbon factors, compare the proposed building to a notionally similar one, or require a second SAP calculation to be performed. Rather than attempting to quantify CO₂ emissions; the methodology remains firmly focussed on the annual energy demand and annual energy consumption and the contribution made by zero-carbon renewable energy sources as calculated for the proposed building. The aim in this approach is to keep the focus on variables that architects, developers and planners can easily identify with and manipulate by taking good decisions in these early stages of the design process.

Compliance is evidenced by completing a standard excel spreadsheet using data extracted from the SAP calculation (Appendix C: Proposal 2). Although more complex than proposal 1, the spreadsheet should take no more than 10 minutes to complete and excel performs all necessary calculations automatically. Used alongside SAP data, the compliance spreadsheet can be exploited as a design tool for architects, developers and planners to objectively explore these different options.

Overall, both proposals actively consider protecting the ability to deliver essential domestic infrastructure such as social and affordable housing as a critical parameter. This is achieved by focussing on the impact of the proposals on the sub-group of dwellings in the 45m² to 100m² size range (Appendix E). However, the use of SAP data to quantify LZCGT contributions does mean that neither proposal truly addresses the intransigent issue of the stage in the design process at which this data becomes available and the implications this has in terms of enforcement and delivering better built outcomes.