Planning policy - section 3F: research

7. Conclusions

In responding to the brief we have considered both the established 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, in conclusion, it is necessary to comment on the strengths and weaknesses of each proposal, and highlight the limitations of some of the assumptions made in formulating these approaches, target levels, and workflows for demonstrating compliance.

7.1 The Scenarios

Both proposals took an essentially pragmatic approach to determining target levels; 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 (Table 10). 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; 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). Potentially this data will need to be revised slightly if the way that annual energy demands are calculated is changed with the adoption of SAP10 (BRE, 2019, pp 73-75). However as each proposal focusses on the subgroup of dwelling in the 45m² and 100m² size range this change is not expected to impact substantially on the recommendations made herein. Each proposal employed the data contained in these scenarios in different ways.

7.2 Proposal 1

Proposal 1 satisfies the research objectives as stated in the brief relative to Section 3F Policy as enacted in current legislation. Although Section 3F is a single issue policy, the proposal acknowledges that other factors also contribute to reducing emissions from buildings. It therefore 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.

The methodology used to determine an appropriate LZCGT contribution level was simple and pragmatic. The scenarios were used to explore what would be a reasonable expectation of the contribution LZCGT would make to the annual energy demand in new buildings under different CO₂ emission reduction standards. This was achieved by gauging the impact on annual energy demand of utilising LZCGT to either replace a proportion of the annual energy demand or generate electricity to offset that demand, and identifying real-world practical limitations that might be encountered in doing so.

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. In exercising this judgement it was recognised that setting a minimum LZCGT contribution that was too high might have unintended adverse consequences on long-term goals for CO₂ emission reduction, energy security and the ability to achieve wider societal goals. It was also acknowledged that what is 'reasonable' is open to interpretation. As a consequence the level of LZCGT contribution calculated by this method was 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). The results were 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. Three alternative ways of defining LZCGT contribution relative to CO₂ emissions were identified in current Section 3F policies: A%, C% and E%. The relationship between these metrics is defined by Figure 8.

We found several distinct advantages to be gained from a regulatory standpoint of using the metric C%, as this 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 percentage indicated in Table 9 the building is in compliance. For C% this has been calculated as 12% for both domestic and non-domestic buildings under all emission reduction standards.

7.3 Proposal 2

By contrast 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 lessons and insights from undertaking the study. It re-invents this policy in a way that focuses on the strengths, skillsets and wider objectives of Planning whilst complementing and supporting the existing whole building approach to CO₂ emission reduction taken by Building Standards. This proposal concentrates on domestic buildings only, 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.

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 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. Policy compliance will be established by completing a simple standardised spreadsheet with data taken directly from the building's SAP document.

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.

The AAED/Capita was established with respect to the predicted annual energy demand (AED) and assumed occupancy (N) of modest-sized dwellings. For the purpose of this study a modest-sized dwelling was defined as between 45m² and 100m². This size range was defined with reference to statistical data and provides the critical cut-off points in calculating the target AAED/Capita level (BRE, 2008; Joyce, 2011; Scottish Government, 2017b; Appendix E). It also acknowledges the excess per capita energy consumption in large dwellings due to their large heated living space and relatively low average occupancy rates (BRE, 2008; Burford et al., 2019). Scenario 2 and 3 were used to define the AAED/Capita for 2021 and 2024 respectively.

This AAED/Capita will apply to all dwellings regardless of size. However by calculating this value with respect to modest sized dwellings the target rate can 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. It is recognised that it will be potentially more challenging for large dwellings, but it is still readily achievable (Appendix C). 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 passive design principles or 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 substantial CO₂ emission reductions in this sector (Appendix E).

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 an unashamedly 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. Making the use of zero-carbon energy sources compulsory only if a building fails to meet its acceptable annual energy demand effectively promotes and rewards sensible passive design decisions and good fabric energy efficiency standards, and allows these factors to do much of the heavy lifting in reducing emissions. Only taking into account high quality zero-carbon energy sources (renewables, heat pumps and heat recovery) also effectively dis-incentivises low-carbon approaches and small scale biomass without carbon capture in line with recommendations made by the Committee on Climate Change (2018).

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. The compliance documentation was designed with the objective of making the entire process as easy and transparent as possible for all stakeholders. 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 or employing additional zero-carbon renewable energy systems. 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.

7.4 Both Proposals

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.

The compliance procedure for both proposals is based around a simple standardised spreadsheet that should take no more than 10 minutes for the building's designer to complete. This will help promote clarity in terms of the evidence required to show compliance and develop familiarity with the compliance procedure. Hopefully it will also address some of the issues regarding the standard of evidencing currently being received by planning officers.

Both proposals depend on data extracted directly from the SAP worksheet so should incur little in terms of additional expense. Although as proposal 1 does require a second SAP calculation so some small costs might be incurred. The use of SAP data to quantify LZCGT contributions does however 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.