Building regulations - energy standards and associated topics - proposed changes: consultation

Part 2 – Energy, new buildings

2.1 Introduction

This section of the consultation covers the process of demonstrating compliance of a new building with standard 6.1 of Building Regulations via the application of the SAP or SBEM calculation methodology. It addresses the process of setting and meeting performance targets under that standard. Proposed revisions applicable to both new buildings and work to existing buildings are addressed within Section 3 of this document.

Consultees may be familiar with the current approach, under standard 6.1, to setting overall emissions targets for new buildings. This uses one or more example specifications which define a ‘notional building’ for which energy demand and a ‘target emissions rate’ are then calculated. The calculated emission for the proposed (actual) building should not exceed this target.

This overall emissions standard is supported by additional standards and guidance within Section 6 (energy) of the Technical Handbooks on the minimum performance of elements of building fabric and services and on the commissioning of systems and provision of information to the building user.

Through revision of standard 6.1, this review presents two options to further improve the energy performance of new buildings using the draft amended UK methodologies (SAP 10 and SBEM version 6), whilst retaining a modified ‘notional building’ approach. In considering this, we also propose amendments to the definition of the notional building to both continue to place an emphasis on low and zero emissions heat systems and offer an effective approach to energy demand reduction.

Work undertaken to define possible amended targets and assess the likely cost of their implementation is set out in published domestic and non-domestic research papers:

• Review of energy and emissions targets set for new domestic buildings.
• Review of energy and emissions targets set for new non-domestic buildings.

The outcomes sought from this research were to:

• establish options for a new notional building specification and illustrate the associated costs and benefits arising from change;
• investigate a new primary energy target to meet a provisions of the 2018 amendment to the EU Energy Performance of Buildings Directive; assess the implications of this to design solutions.
• consider an approach that will also support transition to low and zero emissions heat systems in advance of the proposed 2024 New Build Heat Standard, whilst still retaining viable options for fossil fuel heating systems at this time.

The higher of the two options proposed is intended to illustrate a specification that sets out an achievable but challenging level of ambition in support of the implementation of the 2024 Heat Standard. However, we seek views on both options as the potential standard for implementation in 2022.

This section sets out the areas of change proposed in relation to the delivery of new buildings, considering the calculation process set out under standard 6.1 and other activities relevant to the design, construction and testing on new buildings.

Following review of standards set for new buildings, consequential changes will be made to section 7 (sustainability) and the guidance to standard 7.1 to reflect the amended baseline performance of new buildings under the revised standards.

Any changes implemented following this consultation will adopt the new version of the UK calculation methodologies, SAP 10 and SBEM version 6, which include a range of improvements and enhancements to each methodology and adopt revised fuel emission factors and primary energy factors.

Research into the level of improvement deliverable by an improved notional building specification was undertaken using the information available on these new editions in 2020. Use of the pending new version of the methodologies and associated data enables us to report only the benefit derived from amendment to target setting via Building Regulations. And not on the benefit derived from amendment of the calculation methodology itself, including the significant revision to factors used in the calculation of emission and primary energy performance.

2.2 Proposals

2.2.1 Introduction of an energy target for new buildings

Standard 6.1 (carbon dioxide emissions) has, since 2007, set an overall performance target for new buildings via the calculation of ‘target emission rate’ using the SAP and SBEM methodologies; a target which should not be exceeded by the calculated emissions for the actual building.

However, to support a more informed approach to design and to the delivery of buildings which have very low energy demand, we are proposing the introduction of a further target, using calculated energy demand as the metric. This will become increasingly relevant as the decarbonisation of fuels, such as grid supplied electricity, continues and in the context of 2024 heat standard proposals, to require new buildings to use only ‘zero direct emissions’ heat sources.

As one of our key aims is to further reduce greenhouse gas emissions, it is intended to also retain the current process of setting emissions targets for new buildings. By doing so, we can continue to define a greater challenge in compliance where use of higher emissions fuels is proposed. We will, however, also discuss if there are situations where the emissions metric may no longer be needed to achieve this aim (see section 2.2.11).

A requirement of the 2018 amendment to the Energy Performance of Buildings Directive, set out in Annex 1 of that document, is that Member States adopt primary energy as the principal metric for compliance with minimum energy performance requirements. This is an action which is currently being considered for implementation across the four UK administrations.

Primary energy is defined as “energy from renewable and non-renewable sources which has not undergone any conversion or transformation process”.

The primary energy demand for a building is already reported on Energy Performance Certificates and is derived by the application of primary energy factors to the calculated total delivered energy (that supplied from external sources) for each fuel used at a building. These factors are listed within the SAP and SBEM documentation and information on how they are derived published on the BRE SAP 10 website^[15].

We therefore propose that the new energy target be defined in terms of primary energy to reflect the provisions set out in the EU Directive. The introduction of this ‘Target Primary Energy Rating’ (TPER) is noted in the consultation Documents:

• Consultation proposals - Section 6 (Energy) Domestic;
• Consultation proposals - Section 6 (Energy) Non-domestic;

And implemented in our consultation versions of:

• iSAP: https://www.scotland.isap.org.uk/ and
• c-SBEM: https://www.uk-ncm.org.uk/download.jsp?id=17.

Primary energy or delivered energy?

Due to the application of factors calculated for each fuel source, use of primary energy and emissions targets can have differing impacts on specific building solution depending on the fuel types used. For example, as a result of grid decarbonisation, emission factors for electricity are now significantly lower than gas whilst primary energy factors for electricity remain higher than gas. This issue and the implications for specification of new buildings is examined within the published research papers noted in section 2.1 above.

Accordingly, we recognise there may also be views on the benefit of a more direct representation of energy demand, such as the calculated ‘delivered energy’ total for a building.

Delivered energy is the amount of energy that needs to be supplied to the building from external sources. This is the calculated energy demand for the building less any offsetting of that demand from the generation of energy or heat onsite from renewable sources. It is the delivered energy total for each fuel supplied to a building to which primary energy and emissions factors are applied.

In addition to the presentation of a proposed Target Primary Energy Rating, the calculated total for delivered energy for the notional and actual building are also presented in the consultation versions of iSAP and cSBEM. This is to inform discussion on the preferred metric (primary or delivered energy) for the new performance target.

Question 1 –

Do you support the extension of standard 6.1 to introduce an energy target in addition to the current emissions target? If yes, do you have a view on the metric applied – primary or delivered energy?

Yes, a primary energy target

Yes, a delivered energy target

No

Please provide a summary of the reason for your view below.

2.2.2 Options for uplift in standards for new dwellings

At present, emissions targets for new homes are generated within SAP tools by the application of a published ‘notional building’ specification describing the energy-related characteristics of the building. These are applied to a building model which matches the form and extents of the proposed dwelling.

Under the 2015 regulations, there are five notional building specifications which are applied based upon the chosen fuel for space heating in the actual dwelling (mains gas, LPG, oil, electricity, biofuel). In addition to the elements described for each heating fuel, a set of standard assertions are also applied for other characteristics and elements of the dwelling. The current notional building specification includes an element of on-site generation (PV) for the three fossil fuel packages and applies a modest efficiency air source heat pump for the electrical package.

In the 2015 standards, the level of reduction in emissions for fossil fuel solutions was approximately twice that of electricity and biofuel solutions, whilst ensuring that such solutions remain practicable. This reflected both the previous review to improve the electricity notional building and Ministers’ stated objectives to progressively move away from higher emissions heating solutions. In this current review, we are seeking to continue that trend, in recognition of proposals to decarbonise heat in new homes from 2024. And to respond to evidence that further improvement in building fabric (‘fabric first’) did not become commonplace as an element in the specification of post-2015 new homes.

Development of proposals

Research was undertaken in 2019-20 to identify the capacity for further improvement in the overall energy and emissions performance of new dwellings. Analysis was based upon a set of six dwelling types/variants: detached home, semi-detached home, mid-terrace house and ground, mid and top floor flats, modelled in a block configuration. These were used, together with analysis of data on recent dwelling completions to provide a national baseline profile from which the impact of the proposed changes can be established.

The building energy modelling was undertaken using a consultation version of SAP 10 (iSAP) with updated emission and primary energy factors; these factors can be found in the consultation version of SAP 10.1 on the BRE website. The research contractor provided current capital and lifecycle cost data for Scotland and the resultant cost benefit analysis is presented in the research paper and summarised within the accompanying Business and Regulatory Impact Assessment.

These proposals were put to a building standards Working Group comprised of representatives from across the built environment sector in a series of meetings between January and May 2021. The research paper which informs these proposals can be found at https://www.gov.scot/ISBN/978-1-80201-194-4.

The intent was to investigate options for further improvement in calculated building performance and how the current provision of five specifications or ‘fuel packages’ could be simplified when defining a revised notional building specification.

It was determined that a single notional building set using gas heating would result in a significant benefit from use of an electric heat pump solution which may not be countered by the setting of robust elemental backstops for building fabric. Similarly, setting targets with an electric heat pump solution would make compliance for other fuels challenging, due to the far higher heat generation efficiency typical of such solutions available to the market.

The option to retain more than one notional building can address both these issues, albeit it would result in two sets of energy and emissions outcomes (as is the case with the current approach across five fuels).

It was recognised that it is difficult to seek to compare other solutions directly with an effective heat pump specification. Given that it is not the intent of this review to preclude the use of gas or other fossil fuels, it was considered that two notional building specifications should be employed, one for heat pump solutions and one, based upon mains gas, for all other solutions. This is set out on page 70 of the supporting research report.

Options for implementation

Accordingly, these are applied to two specification options for overall levels of improvement.

Option 1: ‘Improved’ standard:

• Notional Building 1 - Air Source Heat Pump (ASHP) + improved fabric + natural ventilation (‘ASHP improved’), where dwelling is heated by a heat pump.
• Notional Building 2 - Gas boiler + improved fabric + natural ventilation + PV (‘Gas improved’), where dwelling is heated by any other means.

Option 1 results in an aggregate emissions reduction of 32% over the 2015 standards assuming no significant change in fuel mix reducing heat demand by identifying improved building fabric values; glazing achievable with double glazed units; fabric infiltration of 5 m³/(m².h)@50Pa and use of intermittent extract fans with trickle vents.

In terms of national outcome, Option 1 (improved) results in:

• An aggregate 32% reduction in annual emissions which, when factoring in anticipated changes to emissions factors from 2021 to 2045, equates to a net reduction in emissions for the build over that period of 22%
• The latter is reduced to 18% if an assumed 50% of on-site generation exported to the grid is excluded from calculations (see section 2.2.10).
• An increase in capital cost of construction of between 3% to 4% is identified for this option.
• Savings in fuel costs, assessed for a 60 year period, would accrue but do not offset the initial additional capital cost.

Option 2: ‘Advanced’ standard:

• Notional Building 1 - Air Source Heat Pump (ASHP) + advanced fabric + MVHR (‘ASHP advanced’), where dwelling is heated by a heat pump.
• Notional Building 2 - Gas boiler + advanced fabric + MVHR + PV (‘Gas advanced’), where dwelling is heated by any other means

Option 2 results in an aggregate emissions reduction of 57% over the 2015 standards assuming no significant change in fuel mix - reducing heat demand by identifying more stringent building fabric values; glazing achievable with triple glazed units; fabric infiltration of 3 m³/(h.m²)@50Pa and use of mechanical ventilation and heat recovery.

In terms of national outcome, Option 2 (advanced) results in:

• An aggregate 57% reduction in annual emissions which, when factoring in anticipated changes to emissions factors from 2021 to 2045, equates to a net reduction in emissions for the build over that period of 45%
• The latter reducing to 39% if an assumed 50% of on-site generation exported to the grid is excluded from calculations (see section 2.2.10).
• An increase in capital cost of construction of between 5% to 7% is identified for this option.
• Savings in fuel costs, assessed for a 60 year period, would accrue but do not offset the initial additional capital cost.

Both option 1 and 2 apply a similar building services specification, with reduced flow temperatures (<55 ºC) wet heating systems. Wastewater heat recovery and photovoltaic panels are specified for the gas national building. An increased area of photovoltaics is proposed but based upon building foundation area, to reflect available roof space, resulting in a proportionally lower provision being assigned to flats as the height of a block increases. The contribution of on-site generation to the notional building is also capped to reflect the proportion of generation which can be used at the building (see section 2.2.10 for further details).

National outcome – emissions savings

Table 1 New dwellings – annual abatement compared to 2015 standards – Proposed reduction.

New Dwellings	Option 1 – ‘Improved’	Option 2 – ‘Advanced’
Annual abatement (%)	32%	57%
Annual abatement (kT)	7 kT CO2e	13 kT CO2e

The above national outcomes are derived from applying the emission reductions calculated for individual dwelling cases to a national build annual profile. This build profile, which remains based predominantly on mains gas solutions, is set out in section 1.4 of the domestic research report. The reductions for individual dwelling examples are noted in Table 1 below.

Table 2: Emissions reduction against 2015 baseline for Option 1 and 2 notional building specifications (dwellings).

Dwelling Type Modelled scenario	Detached house (mains gas)	Semi-detached house (mains gas)	Semi-detached house (ASHP)	Mid-terrace house (mains gas)	Flat (average) (mains gas)
Option 1 - Gas ‘improved’ case	34%	34%	N/A	36%	24%
Option 2 - Gas ‘advanced’ case	61%	60%	N/A	62%	48%
Option 1 - ASHP ‘improved’ case	75%*	75%*	39%	74%*	74%*
Option 2 - ASHP ‘advanced’ case	80%*	80%*	51%	80%*	80%*

* applies only where change of heat source from mains gas boiler to air source heat pump.

The full detail of both specifications are set out in clause 6.1.2 of ‘Consultation proposals - Section 6 (Energy) Domestic’.

A consultation modelling tool which implements these two options is available online at https://www.scotland.isap.org.uk/.

We seek your views on both of these options.

Question 2 –

What level of uplift to the 2015 standard for new dwellings do you consider should be introduced as an outcome of this review?

Option 1: ‘Improved’ standard (32% emissions reduction)

Option 2: ‘Advanced’ standard (57% emissions reduction)

Another level of uplift

Please provide a summary of the reason for your view.

2.2.3 Options for uplift in standards for new non-domestic buildings

At present, emissions targets for new non-domestic buildings are generated within approved SBEM or DSM tools by the application of a published ‘notional building’ specification describing the energy-related characteristics of the building. The specification, which is set out in guidance to standard 6.1 and in the 2015 NCM Modelling Guide, is applied to a building model which matches the form and extents of the proposed building.

Under the 2015 regulations, there is a single notional building specification, applied throughout the building on a zone by zone basis, with variant elements – for building fabric (based upon ventilation strategy), infiltration and glazing assertions (based upon glazing location/presence) and the choice of space and water heating solutions (the fuel proposed in the actual building is applied in the notional building, with a defined efficiency). Default assertions for cooling, lighting and auxiliary energy use are assigned.

The 2015 notional building includes an element of energy offsetting via onsite generation of power using PV as a proxy, assigning capacity based upon the lesser of two values derived from gross internal area or roof area.

The 2015 standards saw a move away from use of mains gas (or oil if mains gas is unavailable) as the fuel of the notional building, to application of the same fuel for both setting and meeting the emissions target. This change was made mainly to recognise that inappropriate specification of biofuels could enable compliance to be achieved with far higher level of energy demand than fossil fuel or electric solutions.

In this current review, we are seeking to continue that focus on targets that support the delivery of an energy efficient new building which can utilise the fuel that is most appropriate for its type and location whilst also recognising the intent to regulate for Zero Direct Emissions heat solutions from some point at or soon after 2024^[16]. This suggested a similar approach to that taken for domestic buildings in terms of a more consistent approach to notional building options. We sought to investigate whether this, combined with the proposed Primary Energy metric, can be well-aligned with the intended heat policy trajectory.

Development of proposals

Research was undertaken in 2019-20 to identify the capacity for further improvement in the overall energy and emissions performance of new non-domestic buildings. Analysis was based upon a set of seven different building types (shallow plan and deep plan office, hospital, hotel, primary school, retail unit and warehouse), with variant modelling of main heating fuel giving 12 cases. These were used, together with analysis of recent EPC data on building completions to enable projection of a national profile from proposed changes to specification.

The building energy modelling was undertaken using the current version of SBEM, but with application of projected emission and primary energy factors; these factors are noted within the research report. The research contractor provided current capital and lifecycle cost data for Scotland and the resultant cost benefit analysis is presented in the research paper and summarised within the accompanying Business and Regulatory Impact Assessment.

These proposals were put to a building standards Working Group comprised of representatives from across the built environment sector in a series of meetings between January and May 2021. The research paper which informs these proposals can be found at https://www.gov.scot/ISBN/978-1-80201-192-0.

The intent was to investigate options for further improvement in calculated building performance and whether a more simplified allocation of fuel types within the notional building, with an emphasis on renewable solutions, would be beneficial in driving energy and emission reduction.

The use of an electric air source heat pump (ASHP) was identified as one viable solution and this was assessed against an alternate specification using a gas boiler solution with building performance augmented by on-site generation (with PV as the example solution). The research report also identified practical limitations associated with the use of generating technologies to offset demand and reduce delivered energy. In brief, it also identified that it would not be practical nor desirable to set two such specifications in a way which delivered broadly equivalent outcomes for all buildings. This would require either significant generation capacity (in the gas notional building) or specification of an unrealistically low efficiency for the ASHP building. This is set out from page 64 and page 79 of the supporting research report.

The option to retain more than one notional building can address both these issues, albeit it would result in two sets of energy and emissions outcomes (as is the case with the current approach where the same fuel is assigned to both notional and actual building). Proposals therefore offer a simplified approach in that the notional building is based on only two fuel types, with values assigned to fabric set irrespective of the heating and ventilation strategy applied.

The research did initially investigate three options, including a ‘low’ option which was based upon the most challenging specification currently applied for fabric under the 2015 standards. As this option resulted in relatively low level of further abatement, analysis was not progressed further and it is not offered as a proposal within this consultation.

Options for implementation

Accordingly, two notional building specifications are applied to two specification options for overall levels of improvement.

Option 1: ‘Medium’ standard:

• Notional Building 1 – 400% Air Source Heat Pump (ASHP); improved fabric + ventilation with heat recovery, if building is heated by a heat pump.
• Notional Building 2 - Gas boiler and PV (Gas+PV); improved fabric + ventilation with heat recovery + PV, if dwelling is heated by any other means
  • Option 1 results in an aggregate emissions reduction of 16% over the 2015 standards assuming no significant change in fuel mix reducing heat demand by identifying improved building fabric values; glazing achievable with double glazed units; fabric infiltration of 4 m³/(m².h)@50Pa.

In terms of national outcome, Option 1 (medium) results in:

• An aggregate 16% reduction in annual emissions (without fuel switching) which, when factoring in anticipated changes to emissions factors from 2021 to 2045, equates to a net reduction in emissions for the build over that period of 14%.
• The emissions reduction increases to 60% should electric heat pump solutions be adopted in lieu of mains gas. Again, when factoring in anticipated changes to emissions factors from 2021 to 2045, that equates to a net reduction in emissions for the build over that period of 44%
• The variation in reduction in modelled building types arises from the significant difference in energy profile across those types.
• At present, it is assumed that PV output is used onsite with negligible export. This will be reviewed subject to consultation feedback on section 2.2.10.
• An increase in capital cost of construction of up to 4% is identified for this option.
• Savings in fuel costs, assessed for a 60 year period, would accrue in the majority of modelled examples but do not offset the initial additional capital and renewal costs.

Option 2: ‘High’ standard:

• Notional Building 1 – 435% Air Source Heat Pump (ASHP) + further improved fabric + ventilation with heat recovery, if dwelling is heated by a heat pump.
• Notional Building 2 - Gas boiler and PV (Gas+PV); further improved fabric + ventilation with heat recovery + PV, if dwelling is heated by any other means

Option 2 results in an aggregate emissions reduction of 25% over the 2015 standards assuming no significant change in fuel mix reducing heat demand by identifying more stringent building fabric values; glazing achievable with triple glazed units; fabric infiltration of 3 m³/(h.m²)@50Pa.

In terms of national outcome, Option 2 (high) results in:

• An aggregate 25% reduction in annual emissions which, when factoring in anticipated changes to emissions factors from 2021 to 2045, equates to a net reduction in emissions for the build over that period of 21%
• The emissions reduction increases to 62% should electric heat pump solutions be adopted in lieu of mains gas. Again, when factoring in anticipated changes to emissions factors from 2021 to 2045, equates to a net reduction in emissions for the build over that period of 47%
• The variation in reduction in modelled building types arises from the significant difference in energy profile across those types.
• At present, it is assumed that PV output is used onsite with negligible export. This will be reviewed subject to consultation feedback on section 2.2.10.
• An increase in capital cost of construction of between 1% to 5% is identified for this option.
• Savings in fuel costs, assessed for a 60 year period, would accrue in the majority of modelled examples, but do not offset the initial additional capital and renewal costs.

Both option 1 and 2 apply a similar building services specification, with reduced flow temperatures (<55 ºC) wet heating systems. Specification of electric heating and cooling systems is further improved in the ‘high’ option. An increased area of photovoltaics is proposed but based upon either gross internal area of roof area, whichever option results in the lesser array size. Application of PV within the notional building is omitted where heat is provided via a heat pump. As with new dwellings, the contribution of on-site generation to the notional building is also capped to reflect the proportion of generation which can be used at the building (see section 2.2.10 for further details).

National outcome – emissions savings

Table 3 New buildings – annual abatement compared to 2015 standards – Proposed reduction.

New Non-domestic buildings	Option 1 – ‘Improved’	Option 2 – ‘Advanced’
Annual abatement (%)	16%	25%
Annual abatement (kT)	1.7 kT CO2e	2.6 kT CO2e

The above national outcomes are derived from applying the emission reductions calculated for individual building cases to a national build annual profile. This build profile, which reflects the current fuel mix in new development, is set out in section 1.10.2 of the non-domestic research report. The reductions for individual building examples are noted in Table 4 below.

Table 4: Emissions reduction against 2015 baseline for Option 1 and 2 notional building specifications (non-domestic). Modelled scenario for each building type.

Modelled scenario	Deep Office; Gas; AC	Deep Office; Elec; AC	Hospital; Gas; NV	Hotel; Gas; NV	Hotel; Gas; AC	Primary School; Biomass; NV*	Primary School; Gas; MV	Primary School; Gas; NV	Retail; Gas; AC	Retail; Elec; AC	Shallow Office; Gas; NV	Warehouse Distribution; Gas; NV
Option 1 ‘Gas+PV’	34%	NA	17%	4%	4%	-174%	19%	16%	48%	NA	25%	12%
Option 2 ‘Gas+PV’	45%	NA	22%	11%	10%	-130%	38%	30%	52%	NA	47%	22%
Option 1 ‘ASHP’	34%	20%	74%	75%	66%	-27%	44%	61%	47%	42%	66%	67%
Option 2 ‘ASHP’	36%	23%	76%	78%	68%	-16%	48%	65%	48%	43%	70%	70%

* increase in calculated emissions due to modelling with a higher emissions fuel.

The full detail of both specifications are set out in guidance to standard 6.1 of ‘Consultation proposals - Section 6 (Energy) Non-domestic’ and in more detail within ‘Consultation proposals - NCM Modelling Guide for Scotland’.

A consultation tool which implements these two options is available to download from the UK NCM website at https://www.uk-ncm.org.uk/download.jsp?id=17.

We seek your views on both of these options.

Question 3 –

What level of uplift to the 2015 standard for new non-domestic buildings do you consider should be introduced as an outcome of this review?

Option 1: ‘Medium’ standard (16% emissions reduction)

Option 2: ‘High’ standard (25% emissions reduction)

Another level of uplift

Please provide a summary of the reason for your view.

2.2.4 Elements forming the Domestic Notional Building Specifications

For Option 1 and Option 2, the notional building specification is set out in clause 6.1.2 of ‘Consultation proposals - Section 6 (Energy) Domestic’.

The purpose of the notional building specification is to set an overall performance target for a new building – in this case the Target Emissions Rating and the proposed Target Primary Energy Rating. The notional building specification is not intended as a construction specification as it will not reflect the cost optimum specification for any given dwelling.

However, each of the elements identified for the notional building should be achievable using current construction techniques and solutions. In that context, your feedback on the level of specification set out is also sought.

Question 4 –

Do you have any comments or concerns on the values identified for the elements which make up the Domestic notional building specification for either option, e.g. in terms of their viability/level of challenge?

Yes

No

If yes, please provide your comments.

2.2.5 Elements forming the Non-domestic Notional Building Specifications

For Option 1 and Option 2, the notional building specification is set out in clause 6.1.4 and 6.1.5 of ‘Consultation proposals - Section 6 (Energy) Non-domestic’ and in more detail on pages 8 to 22 of ‘Consultation proposals - NCM Modelling Guide for Scotland’.

The purpose of the notional building specification is to set an overall performance target for a new building – in this case the Target Emissions Rating and the proposed Target Primary Energy Rating. The notional building specification is not intended as a construction specification as it will not reflect the cost optimum specification for any given dwelling.

However, each of the elements identified for the notional building should be achievable using current construction techniques and solutions. In that context, your feedback on the level of specification set out is also sought.

Question 5 –

Do you have any comments or concerns on the values identified for the elements which make up the Non-domestic notional building specification for either option, e.g. in terms of their viability/level of challenge?

Yes

No

If yes, please provide your comments.

2.2.6 Change to fuel assignment of the notional building – Domestic

At present, the fuel used in the notional building specification is, generally, the same as the proposed building meaning the emissions intensity of the fuel used is not a significant factor in determining the target that must be met. The principle of this approach was to set a challenging target, in energy demand terms, for every building irrespective of the fuel used to heat the building.

A key objective of research to support this review was to explore the option of moving to a single or simplified notional building specification in 2021 which would not vary as greatly by fuel type. The intent being to set a performance target based on a fuel with relatively low emissions and primary energy factors. This could assist in the transition to the mandatory requirement for new dwellings to operate with zero direct emission heating systems that is proposed will take effect from 2024. This is discussed in sections 4.5 and 5.1 of the research report^[17].

As noted in section 2.2.2, we propose to move away from the current set of five notional building specifications, determined by the main heating fuel in the actual building, to two specifications, based upon the approach to provision of heating at the building. A specification will be assigned based upon use of a heat pump for space heating or, in recognition of the greater efficiencies achievable by that solution, separately for the use of any combination of fuel and heat source.

It is recognised that the performance targets generated by these two routes will differ significantly due to the difference in efficiency of the two assigned heat generators (air source heat pump and gas boiler). For non-heat pump solutions, targets will be set using an efficient gas boiler specification with energy demand offset by the inclusion of on-site generation (photovoltaics) within the notional building specification.

The intent behind this approach is to recognise the practical limits of each route in reducing energy demand in new homes and reflect that in target setting. Each route defines a challenging specification for the chosen approach to heat provision which should, in all cases, result in a delivered energy total which is less than the calculated energy demand for the dwelling.

Removal of a notional building specification for oil, LPG and biomass recognises the intent set out in proposals for the 2024 New Build Heat Standard to move away from solutions that generate emissions at point of use. This also creates a more challenging target, to reduce overall energy demand where higher emissions fuels are proposed. It is noted that these proposals will increase the challenge to deliver new homes with oil or gas heating in areas without access to mains gas.

The detail of this proposal is set out in clause 6.1.2 of ‘Consultation proposals - Section 6 (Energy) Domestic’. The development of the proposal is summarised on page 70 of the supporting research report.

Question 6 –

Do you have any comments on the simplified two-specification approach to defining the Domestic notional building from 2022?

Yes

No

If yes, please provide your comments.

2.2.7 Change to fuel assignment of the notional building – Non-domestic

Whilst the current approach taken in setting emission targets for new non-domestic buildings differs slightly from that for new dwellings, the same general approach is taken.

As noted in section 2.2.3, we propose to move from the current approach to assigning the fuel(s) chosen for the proposed (actual) building to the notional building. As with the new Domestic proposals, we propose to move to just two variant specifications, based upon whether space heating at the proposed building is met by a heat pump or by any other solution. The assignment of on-site generation within the notional building (photovoltaic panels) would be applied proportionately, to the extent that space heating is provided by a non-heat pump solution.

The development of the proposal is summarised on page 70 of the supporting research report^[18] and in in clause 6.1.4 and 6.1.5 of ‘Consultation proposals - Section 6 (Energy) Non-domestic’ and in table 8 of ‘Consultation proposals - NCM Modelling Guide for Scotland’.

Question 7 –

Do you have any comments on the simplified two-specification approach to defining the Non-domestic notional building from 2022?

Yes

No

If yes, please provide your comments.

2.2.8 Change to assignment of Domestic Hot Water (DHW) – Non-domestic

The assignment of fuel used for water heating in the Non-domestic notional building is now proposed to be considered separately from space heating. For example, if a zone in the actual building uses electric heat pumps for space heating and natural gas for hot water generation, then the equivalent zone in the notional building will use electric heat pumps for space heating and natural gas for hot water generation.

One additional parameter is considered – whether zones within the building have low or high hot water use.

Where an activity set for a zone has high hot water demand, the approach proposed follows that for assignment of space heating within the notional building, with hot water provided from either a heat pump (if a heat pump is proposed) or from a gas boiler (if any other solution is proposed). Where a zone is assigned low hot water use, the notional building will use electric point-of-use heating.

The change in grid generation mix means that the use of electric point-of-use water heaters is no longer a high-emissions solution compared to natural gas. In buildings with low DHW demand, point of use water heating can avoid the losses from storage and secondary circulation loops that are associated with a centralised DHW system.

This approach is summarised on pages 62-66 of the supporting research report^[19] and in clause 6.1.4 of ‘Consultation proposals - Section 6 (Energy) Non-domestic’ and in Table 9 and page 16 of ‘Consultation proposals - NCM Modelling Guide for Scotland’.

Question 8 –

Do you have any comments on the proposal to separate and provide a more demand-based approach to assignment of domestic hot water heating within the Non-domestic notional building specification from 2022?

Yes

No

If yes, please provide your comments.

2.2.9 Supplied heat connections

Background

Our draft Heat in Buildings Strategy^[20] identifies the importance of heat networks as a component in the delivery of low and zero emissions heat in the future. The Heat Networks (Scotland) Act 2021^[21] includes statutory targets to ensure that heat networks supply at least 2.6 terawatt hours of heat by 2027 and 6 terawatt hours of heat by 2030.

As heat networks will play an important role in the heat transition, the new regulatory regime set out in the Heat Networks (Scotland) Act aims to build confidence among consumers and attract investment for growth of the sector. The new regulatory regime for heat networks will become operational by the end of 2023.

In order to support the delivery of Scotland’s climate change targets, all heat networks will need to be powered using low and zero emissions sources, for example from heat pumps or surplus or waste heat. The regulations to be implemented under the Heat Networks (Scotland) Act will govern the future heat generation and emissions characteristics of heat supplied by networks. This will include provision for the decarbonisation of existing heat networks over time.

The Scottish Ministers will set out how the Act will support the achievement of these targets and greenhouse gas emissions reduction targets in the Heat Networks Delivery Plan which will be published by 1 April 2022. This will include developing an approach to the emissions from existing heat networks.

It is important, therefore, that standards set under Building Regulations enable the connection of new buildings to existing and new heat networks where this is an appropriate solution. This should be addressed in a manner which takes into account the long lifetime of a heat network; offering solutions that are equitable in relation to other low or zero emissions fuel choices; and provides assurance that energy demand at the building will be limited to a similar extent as for other heat solutions.

It is recognised that even a very efficient new heat network will be subject to losses which are not present when specifying building-based heat generation solutions. Also, over time, changes to the sources of heat generation contributing to the network are likely – an issue which is outwith the control of the developer or the building owner.

Proposals

Following this clear intent to address the characteristics of supplied heat through separate regulatory mechanisms, we propose to refocus the approach to demonstrating compliance with the revised standard 6.1. This will reinforce the need for Building Regulations to focus on actions which can be delivered at a building level, at the point of original construction, to reduce energy demand and therefore associated emissions.

We propose that compliance with standard 6.1 for a building supplied with heat from an external network source will be demonstrated against the ‘gas’ notional building (as noted in sections 2.2.6 and 2.2.7), but the calculated energy demand totals for the actual building will have the primary energy and emissions factors for grid electricity applied rather than the SAP/SBEM default or network-specific values for supplied heat (as modified by the network characteristics).

This recognises that supplied heat can be utilised with 100% efficiency at the building, with adjustment only needed to recognise any standing losses from heat interface units that do not contribute usefully to reduce the heating demand at the building. Application of these factors enables the designer to demonstrate an equivalent outcome in respect of energy demand at the building, for supplied heat solutions compared to on-site heat solutions.

In short, we will amend the approach to demonstrating compliance with standard 6.1 so that Building Regulations will address only the energy performance of the building whilst the characteristics of the supplied heat will be addressed separately under proposed heat network legislation.

The change proposed:

• Provides an equitable approach to the specification of buildings, for both building-based generation and supplied heat solutions.
• Offers assurance that the energy performance of the new building will be addressed to a similar level, regardless of the heat solution proposed.
• Recognises that the characteristics of supplied heat from networks can vary significantly across Scotland, and over time, making it challenging to establish a consistent good practice standard for the construction of new buildings.

There is reassurance that the characteristics of supplied heat to buildings will be improved through the introduction of regulations made using the powers within the Heat Networks (Scotland) Act 2021. This will address issues of performance and greenhouse gas emissions associated with that supply with no or minimal need for intervention at a building level for new build properties.

This proposal is implemented within our consultation versions of:

• iSAP: https://www.scotland.isap.org.uk/ and
• c-SBEM: https://www.uk-ncm.org.uk/download.jsp?id=17.

Please note: this proposal will only apply to the process of demonstrating compliance with standard 6.1 of the Building Regulations. Calculation of, and reporting on, energy and emission performance in the production of Energy Performance Certificates is unaffected and will remain as set out in the published UK methodologies unless subject to separate review.

Question 9 –

Do you support this change in application of targets for supplied heat connections to new buildings, focussed on delivering a consistent high level of energy performance at a building level?

Yes

No

Please provide a summary of the reason for your view.

2.2.10 Limiting benefit from on-site generation of power.

Background

From the adoption of the SAP and SBEM methodologies to set emissions targets in 2007, Building Regulations have assigned a full emissions credit to electricity generated on site, regardless of whether it is consumed at the building or exported to the local grid. The rationale for this was that such small-scale renewable generation contributed, in a small way, to the decarbonisation of the national grid and offset the amount of power needed from large scale generating sources which were more carbon intensive than at present.

The current review of energy standards within Building Regulations is being undertaken in a policy environment which has evolved to consider the need:

• To decarbonise the heat that we use in all our buildings, starting with new buildings (Heat in Buildings Strategy; Heat Standard 2024), taking an energy systems approach; and
• For a stronger focus on effective reduction of energy demand, and delivered energy in particular, at a building level; and
• To place greater emphasis on the end-benefit outcome delivered by the design and specification choices to the developer.

In this context, it is proposed that the current approach to on-site generation does not provide a useful representation of benefit and can therefore skew both design and specification decisions and assessment of the relationship between calculated and actual building performance.

Additionally, the introduction of an energy target within standard 6.1 requires correct representation of solutions that reduce delivered energy totals, without significant uncertainty over that outcome (such as through an export component).

On the principle that this is amended for the energy calculation, it is incumbent upon us to make the same provision in respect of the current emissions calculation. Noting that, for reporting purposes, the total generating capacity can still be reported outwith the Building Regulations compliance calculation.

Proposals

It is proposed that, for the issue of effective use of onsite generation of power to be considered, the following elements should be addressed.

a. Direct connection to the building electrical supply must exist.

If the generating source does not supply power directly to the building, then no credit should be assigned. Such an installation serves no purpose in reducing energy demand from external sources at a building level.

For example, for domestic buildings, a photovoltaic panel array on a block of flats which is connected only to the landlord’s supply does not act to reduce delivered energy to any dwelling and should be ignored for the purpose of a dwelling-level calculation.

b. Determine the extent that generated power can be utilised - emissions.

The export component of any generating capacity needs to be more properly assessed and the proportion which is in excess of the building’s capacity to use directly or store for future use should be discounted from the building-level emissions compliance calculation. Otherwise a measure which is partially effective in reducing delivered energy is being assigned the same status as a measure that is more effective in doing so.

The exported component can still be reported but would not be counted as part of building-level compliance.

c. Determine the extent that generated power can be utilised - energy.

As noted in section 2.2.1, primary energy is defined as “energy from renewable and non-renewable sources which has not undergone any conversion or transformation process”. Primary energy reports on the total energy needed, at the point of original generation, to meet the energy demand of the building.

The primary energy demand of the building should be determined from the delivered energy totals of the building, with primary energy factors being applied to the net totals after deduction of utilised on-site generation. Where part of that demand is met by on-site generation of heat or power which consumes no fuel, each kWh of onsite generation that can be used will reduce the delivered energy total by an equivalent kWh for the relevant fuel.

If generated energy is exported and leaves the building (the ‘system boundary’ of the SAP or SBEM calculation), it can no longer affect the delivered energy total for the building. Accordingly, the export component of generated electricity should be ignored for the purpose of the building-level compliance calculation for energy, be that reported in terms of delivered energy or primary energy.

It can still be reported separately and that data used to inform aggregated totals of microgeneration export in Scotland or the UK. However, the only effect this component can have is to contribute to the calculation of the network primary energy factor.

As such, BSD propose not to apply the proposed SAP 10 PE factor of 0.501 for ‘electricity sold to grid’ (fuel code 36/60), setting this value to zero for the purpose of the compliance calculation.

Application in practice:

• For SAP, we propose to use the calculation of the beta (β) value to set the limit of credit from electrical generation for both the emissions and primary energy compliance calculation. Using the amended process set out in Appendix M of SAP 10, this can consider the base electrical demand and the benefit of battery storage or a PV diverter (but not currently both).
• For SBEM, we propose to use the calculated energy demand for grid supplied electricity plus (if deemed a relevant output of the methodology) the calculated value for equipment to set the limit of credit for electrical generation for both the emissions and primary energy compliance calculation.

The granularity of this calculation will be limited by the level of detail available within each methodology (e.g. limits via monthly energy totals).

It is important to stress that this is a limiting action that is applied to both the target rating calculation (PV element) and the actual building rating calculation (all generating solutions). It has the effect of moderating, only where appropriate, the contribution that on-site generation has in lowering the target emission/primary energy rate and the manner in which it can be met.

As the proposed notional building specifications have no element of thermal or battery storage specified, there will be the opportunity for designers to introduce such elements to the actual building to increase the level of utilisation of on-site generation where this is a preferred solution. Enabling benefit from generation that would otherwise be curtailed by the export cap.

In summary, we propose the following:

• The revised target setting approach is to exclude that component of on-site electrical generating capacity which is assessed as exported from the property to the electricity grid.
• Benefit from on-site generation of power will be assigned only to the extent that it can be demonstrated, within the SAP or SBEM calculation, that generated energy is retained and used at the building, reducing the need for delivered energy, from external sources. Consultation tools will present this option.
• We are proposing introduction of an additional energy target for new buildings (see section 2.2.1). This principle will also apply to that new metric.
• This change is intended to deliver a more representative illustration of the benefit derived from generation solutions. It will also support informed design decisions on how best to apply such solutions to practical effect, further reducing reliance of new buildings on energy supplied from external sources.

This proposal is implemented within our consultation versions of:

• iSAP: https://www.scotland.isap.org.uk/ and
• c-SBEM: https://www.uk-ncm.org.uk/download.jsp?id=17.

Please note: this proposal is only applied to the process of demonstrating compliance with standard 6.1 of Building Regulations. Calculation of and reporting of energy and emission performance in the production of Energy Performance Certificates is unaffected and will remain as set out in the published UK methodologies unless subject to separate review.

Question 10 –

Do you agree with the principle set out, that the benefit from on-site generation within the compliance calculation should be limited by a practical assessment of the extent that generated energy can be used onsite?

Yes

No

Please provide a summary of the reason for your view.

Are there any particular concerns you have over this approach, e.g. with regards particular technologies or solutions?

2.2.11 Applying standard 6.1 to buildings with only Low and Zero Emissions Heating Systems.

Background

Our draft Heat in Buildings Strategy^[22] defines ‘low and zero emissions heating systems as "systems that have zero direct greenhouse gas emissions such as individual electric heat pumps and connections to heat networks, or electric systems such as storage heaters, and systems that have very low emissions such as those that use hydrogen”.

This is further reflected in the proposed 2024 New Build Heat Standard being confirmed and implemented. The strategic consultation on that Standard^[23], issued in December 2020, defines acceptable heat solutions as follows:

“‘Zero direct emissions from heating and cooling’ will ensure that no greenhouse gas emissions are produced at all from the heating or cooling system contained within a building at the point of use.

We propose that electricity and thermal energy from heat networks would, therefore, be considered ‘zero-rated’ (i.e. considered to produce zero direct emissions at the point of heat consumption)”.

Proposals within this consultation do not prevent the continued use of fossil fuel and other heat solutions which rely upon combustion of fuel at the building. However, revision and simplification of the notional building packages (see sections 2.2.6, 2.2.7 and 2.2.10) are intended to place greater emphasis on the use of such ‘zero direct emissions’ heat solutions, where practicable.

To support this outcome, prior to the implementation of the 2024 Heat Standard, this consultation investigates a range of options which can promote implementation of low and zero emissions heat solutions. The simplification of the notional building specifications is one such action as is the proposal to ‘future proof’ heating installations to support simple installation of ‘zero direct emissions’ heat solutions in the future (see sections 2.2.12).

Proposals

Accordingly, we propose, where the heat and cooling requirements of a new building are met only by solutions which meets the definition of a ‘zero direct emissions’ heat source, that the emissions target set under Standard 6.1 shall not apply to the building.

This would remove the need to demonstrate that a building meets both an emissions and an energy target where a developer has chosen to using only zero direct emissions solutions, in advance of the 2024 Heat Standard. Such a choice means that action to limit greenhouse gas emissions is already demonstrated in the choice of heat solution.

Calculation to demonstrate that the energy target is met would still be undertaken to confirm that energy demand at the building is limited to the appropriate level.

Calculated emissions for the building will still be reported on the Energy Performance Certificate required for new homes and new non-domestic buildings under Standard 6.9 within section 6 (energy). Reporting will, as at present, apply the factors for both emissions and primary energy set out in the updated calculation methodologies (SAP and SBEM). However this information is informative only and, whilst it must report on the performance of the building, as-constructed, it is only the provision of the EPC itself which is required under standard 6.9.

Question 11 –

Do you agree with the proposal that new buildings where heat demand is met only by ‘zero direct emissions’ sources should be exempt from the need for a calculation to demonstrate compliance with the Target Emissions Rate?

Yes

No

Please provide a summary of the reason for your view.

2.2.12 Designing for future retrofit of Zero Direct Emissions heat solutions.

As noted in section 2.2.11, proposals within this consultation do not prevent the continued use of fossil fuel and other heat solutions which rely upon combustion of fuel at the building. This will change with action under the proposed 2024 New Build Heat Standard. There is a similar intent for the for deployment of low and zero emissions heat within our existing building stock by 2040/45.

“By 2045, emissions of greenhouse gases from heating our homes and buildings will have all but disappeared, with demand for energy reduced and space and water heating provided by zero emissions alternatives.”^[24]

From 2024, new buildings will be required to use ‘zero direct emissions’ heat solutions. Until that time, we seek to further reinforce both the consideration of such solutions and to support simple and inexpensive replacement of heat generators such as gas boilers in the future.

Provisions elsewhere in this consultation address the actions needed in the design of a heating system based upon lower temperature heat distribution (see section 3.2.9).

In addition to this, we propose, where a new building is not constructed with a recognised ZDE heat solution meeting all heat needs, that the developer shall provide information detailing the process and work involved to deliver that adaptation, simply and without disruption beyond the immediate vicinity of the current heat source.

Question 12 –

Do you support the need for new buildings to be designed to enable simple future adaptation to use of a zero direct emissions heat source where one is not initially installed on construction. And for information setting out the work necessary for such change to be provided to the building owner?

Yes

No

Please provide a summary of the reason for your view.

Do you have any comments on the level of information needed to support such action in practice or on the extent to which alterations other than those at, or very close to, the heat generator can be justified?

2.2.13 Fabric performance of new dwellings – Domestic

Minimum standards for insulation of new dwellings to limit heat loss are addressed through guidance to standard 6.2 (building insulation envelope). Clause 6.2.1 sets maximum area weighted U-values for elements such as walls, roofs, floors and openings.

Analysis of Energy Performance Certificate (EPC) Data for 2016-2020 dwelling completions, with an increasing number of homed built to the 2015 standards, indicate only a slight improvement in the average U-value for walls. This data indicates that new homes are commonly built to closer to backstop values for fabric than to those values within the notional building specification. It is common to augment a lower fabric specification with increased use of on-site renewables, such as photovoltaic panels (the amount of PV installed has more than tripled in the same period). It is noted that such an approach may not offer the same assurance of benefit in reducing energy demand and the energy delivered to the building as the generated energy is not always used within the building.

The issue of building fabric has a higher profile in more recent years following calls by the UK Committee on Climate Change for new homes to be ‘ultra-energy efficient’ and concerns over increased energy costs associated with the proposed transition to low and zero carbon heat solutions.

Within guidance to Building Regulations, element U-values for the Notional Building are set at an achievable good practice level and it is expected that there must be some ‘leeway’ in the actual performance specified to enable a flexible approach to building design. If this degree of flexibility is reduced, whilst still citing buildable levels of performance, there is more assurance on the delivery of new homes and new work that is as effective as practicable at reducing heat loss.

Accordingly, it is proposed to introduce more robust backstops, which ‘keep pace’ with the improved Notional Building fabric values (to a practicable extent) to drive overall improvement in the building fabric of new homes.

In implementing this for new construction, two options are available:

• Maintaining the elemental approach set out under standard 6.2 at present, but with improvement of both cited values and the prescription attached to the other aspects of heat loss addressed by the standard (losses through thermal bridging at junctions and through air leakage (infiltration). This approach allows the noted degree of flexibility, departing from the level of specification within the notional building to support implementation of a wider range of construction specifications in practice.
• Use a similar specification to define a calculated heat demand target which should be met in the same way as the current emission target. This will encompass U-values, linear thermal bridging, fabric infiltration and also, via the SAP methodology, take into account the design and layout of the building and any beneficial environmental gains that arise. This approach is used in the current definition of the non-mandatory ‘useful energy for space heating’ aspect of our sustainability standard 7.1 and, in English building regulations, for their Target Fabric Energy Efficiency rating.

Further improvement of standards at this time is moving the level of expected performance beyond that which can be delivered with some older construction solutions, such as use of infill insulation only between a timber frame). Adoption of current good practice for fabric specification (e.g. the better half of all built solutions) would provide improved minimum levels of performance which are achievable as simple backstops. Accordingly, setting minimum standards at the level proposed below would appear to remove the need for an overall fabric performance metric.

It is proposed that a better and more consistent level of fabric insulation is achievable in all new construction. Such a standard can be delivered by the capacity and experience already present in the construction and manufacturing sector in Scotland, recognising also the benefits of a greater use of solutions such as off-site manufacture of components.

We propose to retain the current elemental approach to minimum fabric performance and improve recommended maximum area-weighted U-values as set out in the table below. Options are illustrated in clause 6.2.1 in ‘Consultation proposals - Section 6 (Energy) Domestic’.

Table 5: Proposed maximum fabric values for new homes.

Fabric Element	Current (2015) Notional Building U-value	Current (2015) Maximum U-value	Option 1 - Improved Notional Building U-value	Option 1- Improved Maximum U-value	Option 2 - Advanced Notional Building U-value	Option 2 - Advanced Maximum U-value
Wall	0.17	0.22	0.15	0.17	0.13	0.16
Roof	0.11	0.15	0.09	0.12	0.09	0.11
Floor	0.15	0.18	0.12	0.15	0.10	0.13
Doors/Windows	1.4	1.6	1.2	1.4	1.0/0.8	1.2
Rooflights 1	1.4	1.6	1.7	1.9	1.3	1.7
Party Wall	0.0	0.2	0.0	0.0	0.0	0.0
Junctions	0.08	n/a	0.06	n/a	0.04	n/a
Infiltration	7	n/a	5	n/a	3	n/a

¹ U-values for rooflights is calculated on the horizontal plane.

A review of the last years’ EPC data has informed the development of the above range of performance levels assigned to elements of the insulation envelope. For Option 1 (Improved), the maximum U-values cited are the 50^th percentile values from current construction (e.g. achieved by at least half of new construction). Values for Option 2 (Advanced) option are shown as 33^rd percentile (one third of new construction).

Such values are challenging, but achievable, and will result in a significant improvement in levels of fabric performance in all new homes. Application of these amended values would be supported by revised guidance on the principles of reducing heat loss at junctions and through fabric infiltration, reinforcing the need to consider all aspects of the building insulation envelope within design and construction.

To raise awareness of the overall impact of design specification on building fabric performance, we would also seek to report the calculated space heating demand for each dwelling As part of output from SAP tools. This is already an output from the calculation (this is calculated in box 99 of the SAP worksheet) as noted on the previous page.

Where more design flexibility is sought, an alternative solution might be to demonstrate that the overall space heating demand for the dwelling is no more than this calculated total, subject to the use of agreed values for both infiltration and heat loss at junctions – the notional building values are proposed. This provides, in effect, an informal ‘space heating demand target’, applied where elemental values are not used in full to demonstrate compliance.

Thermal Bridging at Junctions

Please note that it is also the intent to cease to provide a set of ‘Accredited Construction Details’ (ACDs) for common constructions in support of amended domestic standards from 2021. This is in line with the approach taken in other UK administrations and reinforces the expectation that such information should be produced, as a matter of course, by the construction sector. The introductory section of the current ACD document, which sets out the principles of addressing thermal bridging at junctions and detailing to reduce infiltration, will be updated and remain a reference publication.

Question 13 –

Do you support the retention of the current elemental approach to setting minimum standards for fabric performance in new dwellings, supported by the option to take an alternate approach via calculation of the total space heating demand for the dwelling (as described)?

Yes

No

Please provide a summary of the reason for your view.

In the context of the proposed approach, If you have any comments on the maximum U-values proposed for elements of fabric, in relation to their level of challenge and achievability at a national level, please set them out below.

2.2.14 Increase in airtightness testing – Domestic

Low air infiltration rates contribute to energy performance of a building by reducing unintended ventilated heat loss. However it can also have an adverse impact on the level of ventilation provision where the infiltration rate is lower than 5 m³/(h.m²)@50Pa and an appropriate ventilation system has not been installed. There is, therefore, a need to establish dwelling performance by test to demonstrate compliance in both these respects.

Air-tightness testing was first introduced to the Technical Handbooks in 2007 as a means to demonstrate that high levels of air-tightness declared at the design stage, were being met at the construction stage and that the ventilation proposed for the dwelling was appropriate for that situation.

Current guidance calls for representative sampling of buildings to be tested at a frequency of at least 1:20. Testing should be carried out by persons who can demonstrate relevant, recognised expertise in measuring the air permeability of buildings. This should include membership of a professional organisation which accredits its members as competent to test and confirm the results of testing.

A review of EPC data for 2020/21 indicates that around one third of new dwellings are subject to an air tightness test and commonly achieving air infiltration rates below 5 m³/(h.m²)@50Pa, with an average test performance of 4.4 - 4.5 m³/(h.m²)@50Pa.

Source: Scottish EPC data for new homes completions March 2020 to March 2021 (publication pending). 15,004 records reporting 5,262 tests (35%).

As this level of airtightness requires greater consideration of the ventilation strategy to be adopted for the building, we propose that all new homes should be tested. This would provide greater assurance that the infiltration rate actually achieved in the dwelling is a fair representation to that declared at the design stage. This will assist in closing the performance gap associated with heat loss through infiltration. It will also, more importantly, provide assurance that the ventilation strategy adopted in the building is appropriate for the level of air infiltration present within the dwelling. See clause 6.2.5 in ‘Consultation proposals - Section 6 (Energy) Domestic’.

Current guidance to standard 6.2 includes the option to not test a dwelling where a default air infiltration rate of 15 m³/(h.m²)@50Pa is declared. Whilst rarely used, this is no longer considered supportable as this is an unrepresentative value, given risk that the dwelling could be constructed to a far tighter level of air infiltration meaning the proposed ventilation strategy is inadequate. It will be removed from guidance.

We intend to strengthen the existing guidance on what level of competence is required from those persons carrying out and reporting on air tightness testing, requiring membership of an appropriate testing organisation.

Question 14 –

Do you support the move to airtightness testing of all new dwellings, by registered members of an appropriate testing organisation?

Yes

No

Please provide a summary of the reason for your view.

2.2.15 Increase in airtightness testing – Non-domestic

Currently, all new non-domestic buildings and large extensions which are subject to Standard 6.1 (carbon dioxide emissions) should be tested on completion, with limited exceptions.

We propose to limit these exceptions further to remove the exception to testing for small multiple units (< 150 m²) and large extensions and reduce the limit for exceptions for modular buildings to those less than 150 m². This is set out in clause 6.2.6 of ‘Consultation proposals - Section 6 (Energy) Non-domestic’.

As with the proposals for new dwellings, we intend to strengthen the existing guidance on what level of competence is required from those persons carrying out and reporting on air tightness testing, requiring membership of an appropriate testing organisation.

Question 15 –

Do you support the move to increased airtightness testing of all new non-domestic buildings, by registered members of an appropriate testing organisation?

Yes

No

Please provide a summary of the reason for your view.

2.2.16 Adoption of CIBSE test methodology

Review of building regulations in England by the UK government has proposed and confirmed adoption of an alternative air tightness testing methodology to that currently cited in the Technical Handbooks, produced by the Air Tightness Testing and Measurement Association (ATTMA). The principal reason for this is to ensure that the approved methodology for airtightness testing is independent of all organisations with an associated competent person scheme. The methodology proposed is TM 23 – ‘Testing buildings for air leakage’ produced by CIBSE, which has recently been revised and updated with such use in mind.

The intent was that the test methodology should be published independently of the approved schemes in England, and that the low pressure pulse method (see section 2.2.17) should also be included in the test method publication

Whilst the building standards system in Scotland does not operate formal competent persons schemes, we would propose to adopt the same methodology to provide consistency of approach to air tightness testing across the UK.

To ensure consistency in process and standards for testing across the UK, we would propose that the updated TM23 also be adopted and cited in Scotland.

Question 16 –

Do you support the adoption of CIBSE TM 23 as the basis for airtightness testing in Scotland?

Yes

No

Please provide a summary of the reason for your view.

2.2.17 Adoption of option to apply ‘pulse’ test

Currently, airtightness is commonly tested by creating a pressure differential of 50 Pascals (via the blower door method) and measuring how pressure changes once the source of pressurisation is turned off. An alternative means of testing at a lower pressure differential of 4 Pascals now exists, having been developed over a number of years. We are seeking views on the introduction of this Pulse Test as an approved airtightness testing methodology.

It is noted that approval of the use of this method has already been signalled in relation to review of building regulations in England. In support of that review, a number of issues flagged in relation to the application of the test method have been clarified, including the practical limits within which testing can be undertaken and the means of conversion of results for reporting to give assurance of comparability with the higher pressure blower door test method. Amendments to the proposed new test methodology TM 23 are also being completed on that basis and provisions for representing results incorporated within SAP 10.2 (currently unpublished).

It is noted that such a test method does not support diagnosis of building defects in the same way that a continuous pressure test can (e.g. identification if infiltration pathways). We therefore see the introduction of a second method of test as complimenting that which is currently available.

Question 17 –

Do you support the introduction of the pulse test method of airtightness testing as a further means to resting and reporting on the performance of new buildings?

Yes

No

Please provide a summary of the reason for your view.

Are there any particular benefits, risks or limitations you would seek to identify?

2.2.18 Modular buildings – Non-domestic

Currently, alternative provisions for new modular buildings are set out within Appendix 6.C of the Non-domestic Technical Handbook. To enable the continued use of existing stocks of building modules and sub-assemblies, subject to fabric insulation meeting limiting U-values, a modifying factor can be applied to increase the Target Emissions Rating (TER) for the new building.

A definition of what constitutes a modular building is provided within that Annex.

This is provided to recognise both the common manufacturing base for UK sub-assemblies and the benefits of reuse of existing sub-assemblies offers in respect of embodied energy savings (subject again to a specified minimum energy performance).

We would propose to maintain an allowance of this type within revised standards, applying it to both the emissions target and the proposed new energy target but with further limitations:

• Allowances within Annex 6.C shall only apply to limited life buildings (those intended to be in place for not more than five years). Buildings that are intended to be permanent shall be subject to standards 6.1 to 6.10 unmodified.
• For limited life buildings subject to standard 6.1, apply a modifier of 1.25 to the calculated emissions and energy targets. This limits the flexibility in the target calculations to a level approximately equivalent to the 2015 standards. A declaration that a limited life building will be on site for not more than two years shall still exempt such a building from standard 6.1 and the compliance calculation.
• Limiting fabric values are set at those applied for all new buildings under the 2015 standards. Noting that these values were not improved in 2015, meaning that the standards can be met with elemental values which were also set for new buildings in the previous 2010 standards, enabling the potential reuse of sub-assemblies manufactured since 1 October 2010. Older manufactured products would require refurbishment to uplift them to current fabric standards.

We consider this strikes the appropriate balance between reuse of better performing modules and sub-assemblies and the need for refurbishment of older stock to be more aligned with current expected levels of building performance for both new and existing buildings. Whilst also supporting provision of small buildings at short notice in distress situations (e.g. due to an emergency).

The detail of this proposal is set out within Annex 6.C of ‘Consultation proposals - Section 6 (Energy) Non-domestic ‘.

Question 18 –

Do you consider this amended provision provides an appropriate balance between:

• the requirement to improve building energy performance in new buildings;
• enabling the reuse of better performing modular elements; and
• enabling use of small units for short term use at short notice?

Yes

No

Please provide a summary of the reason for your view.

2.2.19 General comments on proposal for new buildings

Question 19 –

We welcome any other comments you wish to make on the proposed changes to the setting of performance targets for new buildings or the application of other amended provisions within Section 6 (energy) which apply to the delivery of new buildings.

Where practical, please with a reference to any particular issue in the context of the Domestic or Non-domestic Handbook (or both if applicable) and cite any standard or revised guidance clause relevant to the topic.