Building regulations - energy and environmental standards: consultation on proposed changes

3 Proposed components of the standard - Design

3.1 Introduction

3.1.1. Outcome sought

This section sets out and discusses proposed actions to improve the setting of energy performance and ventilation standards for new buildings, leading to lower energy demand (and reduced running costs) and a healthy indoor environment.

It is important for consultees to be aware that this consultation does not set out the detail of proposed new standards applicable to building design. Such matters will be set out in a second consultation scheduled for summer 2025.

This consultation discusses what can be learned from the approach taken by the Passivhaus standard – its principles and processes. And the extent that such provisions might be implemented within the context of national minimum standards set under building regulations to improve how we deliver very low energy buildings with high levels of environmental comfort (thermal and air quality).

3.1.2. Proposals

This section considers the following aspects of the Passivhaus standard, summarised in section 2 and offers commentary on the proposed approach to deliver improvements on current outcomes.

• Application of a robust and representative calculation methodology.
• The setting of challenging overall targets for energy performance and space heating/cooling demand.
• Use of absolute targets to encourage energy-efficient forms.
• Limits on the infiltration of the building envelope.
• Continuity of insulation across the building envelope.
• Assessing risk of peak summer overheating.
• Use of mechanical ventilation with heat recovery to reduce heating demand and maintain indoor air quality.
• Addressing humidity, internal surface temperatures and ventilation noise for occupant comfort.

3.2 Standard 6.1 and approved calculation methodology

3.2.1. Background

Current overall energy targets require to be set and demonstrated for new buildings under standard 6.1 (energy demand). Compliance is demonstrated through the use of the Standard Assessment Procedure (SAP) for new dwellings and the National Calculation Methodology (NCM, Simplified Building Energy Model (SBEM)) for new non-domestic buildings.

The domestic methodology is implemented through approved third party software tools which are tested and validated against the current SAP 10 specification. The non-domestic NCM is implemented through iSBEM, the free government tool or through approved third party FI-SBEM or DSM (Dynamic Simulation Model) tools. Buildings delivered to the Passivhaus standard have their energy performance calculated using the Passive House Planning Package (PHPP), a methodology not currently recognised under building regulations.

The key outcome sought from a calculation methodology should be that it is robust and representative of the performance of the building, presenting an accurate illustration of the effect that any combination of building elements will deliver. This is necessary to support informed decision making from an early design stage. That representation should approximate the outcome expected in the real world.

In this context, it remains the intent that the primary purpose of such tools is to demonstrate compliance with standards rather than as a design tool or a means of reporting on likely operational performance.

Regulatory relevance

Standard 6.1 (energy demand) requires that “the energy performance is calculated in accordance with a methodology of calculation approved under regulation 7(a) of the Energy Performance of Buildings (Scotland) Regulations 2008”.

The cited regulation describes the criteria for such a methodology but does not list current approved methodologies by name. For the purpose of building regulations compliance, the current methodologies are identified in guidance published in support of standard 6.1.

Accordingly, change in cited methodologies may be implemented without the need to amend regulations.

3.2.2. Domestic buildings

A significant review of the UK calculation methodology for determining the energy performance of dwellings is underway. Information on the current development of the Home Energy Model (HEM) as a replacement to the Standard Assessment Procedure (SAP) can be found at Home Energy Model: replacement for the Standard Assessment Procedure (SAP) - gov.uk (www.gov.uk).

An initial consultation on the model, presented in the context of the Future Homes Standard proposals in England, ran from December 2023 to March 2024. Like SAP, it is proposed HEM will underpin a large number of government policies, making it of critical importance to the delivery of a range of policy objectives.

One of the aims of the current HEM development programme is to provide a tool that can be better tailored to suit use across a range of reporting outputs, with initial work focussed on use as a building regulations compliance tool. To support this, the project separates the model’s core building physics from any policy-specific assumptions, the latter being implemented via ‘wrappers’ – software designed to implement specific processes and required inputs and report tailored outcomes for a particular purpose. This will enable users to adapt and use the model in various contexts, with different inputs and outputs suited to their needs.

HEM development seeks to align with modern international energy modelling standards and the best available technical evidence. The new model simulates energy performance at half-hour intervals (compared to monthly reporting in SAP), to better represent the impact of smart technologies and systems.

To test its ability, HEM is being validated against other building energy models, laboratory data, and monitoring data from real homes. Validation is an iterative exercise, and outcomes will be updated and presented until the model is finalised for use in a live environment during 2025.

The project also seeks to increase the transparency of the calculation methodology. The HEM codebase is published as open source with the aim to develop it ‘in the open’ in future.

Proposal

We propose that, subject to validation of the final core model and a suitable Scottish ‘wrapper’, the new standard will require calculation of energy targets using HEM. SAP will remain in use only for legacy projects being completed under current standards.

The Scottish government continues to be involved in the development of HEM and will deliver a Scottish ‘wrapper’ to illustrate the proposed changes to standards as part of the stage 2 consultation in summer 2025.

During review discussions, it has been commented several times that the current SAP implementation does not represent the performance of very low energy buildings well. This premise will be tested by research currently underway which will report on comparative outcomes from the current and proposed UK tools and from the PHPP tool.

3.2.3. Non-domestic buildings

More modest change is being introduced to the Simplified Building Energy Model (SBEM). The draft Version 7 specification incorporates updates to underpinning databases, some enhancements to input on building services. These include:

• A response to concerns that the tool currently underestimates space heating demand. Following review at a UK level, changes made to the underlying activity database (which attributes occupancy and usage parameters to different spaces) has been introduced where data allows and is of sufficient quality.
• Provisions are introduced to support the production of heat pump system seasonal efficiencies, which works alongside SBEM and can be used to provide data when this is not readily produced by the system designer.
• Improved facility to input data where multiple lighting systems are in use in one zone.

Proposal

We propose that the new standard will continue to require calculation of energy targets using updated SBEM/DSM tools.

The Scottish Government continues to be involved in the development of the NCM and ongoing proposals for further enhancements. A Scotland-specific tool for implementation of building regulations compliance reporting will be developed to illustrate the proposed changes to standards as part of the stage 2 consultation in summer 2025.

3.2.4. The Passive House Planning Package

The Passivhaus standard is supported by PHPP as a design and calculation tool. Delivery of a certified Passivhaus project requires the use of this tool from project inception. Both PHPP and SAP are based on the same standard, BS EN ISO 13790, with only small variations, so present the same building physics model.

PHPP uses local climate data and includes unregulated energy for an overall assessment of actual energy use. It focusses on design and reporting of outcomes close to actual energy performance.

In reporting, PHPP considers the external dimensions of the building in defining the thermal envelope to enable a more accurate assessment of heat loss and gain. The outputs of the tool, which is subject to continuous review and quality assurance, have been validated against real world outcomes.

Information needed to define the building model is more comprehensive in detail than the current SAP and basic SBEM tools and the outputs of the specification input are presented in detail to assist the user in design analysis.

Feedback from practitioners trained in the application of the tool are uniformly positive, on its effectiveness at supporting very low energy design.

Proposal

We consider the UK methodologies to be fit-for-purpose in demonstrating building regulations compliance under standard 6.1 (energy demand), subject to ongoing development of the proposed HEM tool.

As noted above, research will report on comparative outcomes from the current and proposed UK tools and PHPP. This will enable further consideration of PHPP’s use within building standards compliance.

The potential role of Passivhaus Certification using PHPP within the building standards system is also discussed in section 3.7.

Consultation Question 3

On the basis that HEM and SBEM are reviewed and shown to report representative outcomes, do you support the continued use of calculation tools which implement the UK methodologies?

Yes

No

Please provide information on why you agree or disagree or if you consider other actions need to be considered, including your experience of PHPP as a calculation tool.

3.3 Approach to defining overall building energy targets

3.3.1. Background

Current building regulations set an overall energy target under standard 6.1 (energy demand). This target is a delivered energy target. It considers only energy use arising due to components of the building – fabric and fixed building services. Targets are set by applying a ‘notional building’ specification to a building the same size, shape and orientation as the proposed building. In this respect, the target set is a relative target, varying with the type and form of building proposed.

Limits on space heating demand are set only through reference to maximum U-values for planar elements of the building envelope – walls, floors, roofs and openings. Guidance is provided on the benefits of limiting both thermal bridging and infiltration but no prescription is set. The premise being that the performance of such elements must be declared, incorporated in the calculation of the building energy target and will be appropriate for the overall level of thermal performance sought within the design. For new dwellings, the alternative of designing to meet a space heating demand limit is available. This is also a relative target and reflects the form of the proposed building.

Passivhaus sets an absolute target for space heating demand of not more than 15 kWh/m²/yr or a peak heating load of not more than 10 W/m². It also sets an overall Primary Energy Renewable demand (all energy use) of not more than 60 kWh/m²/yr which includes energy use from appliances. Setting absolute performance targets encourages delivery of buildings with an uncomplicated, energy efficient form or requires compensation through improved specification for less optimised designs.

3.3.2. Absolute versus relative targets

The energy performance of a given building is influenced by a large number of factors. For space heating and cooling demand, this includes location, orientation, form factor, fabric specification and proportion and positioning of openings.

The setting of an absolute target, be that for overall energy use or for space heating demand, requires the designer to consider all of these elements and how they contribute to the building energy balance. The solution needed to achieve a given numerical target will vary depending on the aspects of design noted above. The principle behind absolute targets is that each building should be able to achieve the same, consistent level of energy performance. Absolute targets are a strong driver for delivery of energy efficient building form – avoiding complexity in external elements or an unnecessarily great surface area to volume ratio.

The setting of a relative target is based on the principle that the overall level of energy use should be defined by the sum of the building parts, assuming a very good level of specification for all parts. The target set will change to reflect the aspects of design noted above. Relative targets are not a strong driver for delivery of buildings with an energy efficient form, being effectively situation neutral. They do, however, enable a greater degree of standardisation of both built form and specification.

Two approaches:

• Absolute target – every building should reach the same level of performance in terms of a reported energy outcome, specification will vary.
• Relative target – every building should reach the same level of performance in terms of an overall level of specification, reported energy outcome will vary.

It is suggested that both approaches should be supported by a robust set of backstop values for elemental performance. To provide assurance that a balanced approach to the level of specification of energy-relevant elements is achieved.

Regulatory relevance

Targets for new buildings are currently defined through the guidance published in support of Standard 6.1 (energy demand). This guidance currently defines a range of ‘national building’ specifications which are assigned to the proposed building based upon the sources of heat proposed. The specification calculates both targets and the actual building performance within approved software tools.

Should there be support for a move to more prescriptive absolute targets, there is the potential to set these out in the same manner, through guidance. This on the basis that the guidance can reasonably be held to illustrate the level of expectation for action to meet the mandatory standard. In this case, expectation that a defined target value is not exceeded.

A question may be raised over the need to set such a value within a mandatory element of the regulations. As noted in section 2.2.5, prescription on the face of a standard or regulation can significantly limit the range of solutions available to an applicant. If the outcome sought cannot reasonably be delivered in all cases, this may also lead to applications to Scottish Ministers to formally relax or dispense with the provision. Such issues must be considered when determining where direction is placed on a given issue.

Accordingly, change in the approach to target setting may be implemented without the need to amend regulations.

Proposal

We consider that the level of performance that can be achieved through a well defined relative target, such as the notional building approach, delivers an appropriate balance between building performance and flexibility of solution in the delivery of new development.

Retention of a relative target does not offer any further direct emphasis on the benefits of building to achieve an energy efficient form. We do not seek to diminish the importance of this from a design perspective but consider that the role of national standards should be to enable delivery of high quality outcomes with a reasonable degree of flexibility on the route taken. Defining targets in as balanced a manner as is practicable.

There is, however, a need to understand the level of benefit that may accrue through a move to the setting of absolute targets compared to outcomes delivered by a relative target which seeks a similar level of specification. This premise will be tested by research currently underway which will report on comparative outcomes from the current and proposed UK tool and from the PHPP tool, looking at the typical levels of performance achieved through improvements to the current relative approach against the prescription of the Passivhaus standard.

We welcome your views and any illustration of the positive and negative impacts arising from these two approaches to target setting.

Consultation Question 4

Do you support retention of the current approach and the setting of relative performance targets for new buildings through an approved calculation methodology?

Yes

No

Please provide information on why you agree or disagree or if you consider other actions need to be considered.

3.3.3. Main energy compliance metric

The February 2023 energy standards introduced a new compliance metric for new homes – delivered energy. This energy metric was proposed in response to the intent to remove the need to report on building emissions under proposals for the New Build Heat Standard, subsequently implemented from 1 April 2024.

Delivered energy is the energy which needs to be supplied to a building from external sources to meet the building energy demand. It is the most relevant metric for those that occupy or manage buildings and is, in effect, the energy needed for regulated uses (space/water heating, cooling, ventilation, lighting and auxiliary systems).

Passivhaus sets an overall performance target – Primary Energy Renewable – which considers energy demand for all consumption at the property, including cooking and appliances. It applies primary energy factors to the calculated values to derive an overall total consumption value.

Regulatory relevance

As noted in section 3.3.2, targets for new buildings, including the confirmed metric (delivered energy) are currently defined through the guidance published in support of Standard 6.1 (energy demand).

Should there be support for a move to a different metric, there is the potential to define this through guidance. This is on the basis that the guidance can reasonably be held to define the approach taken to demonstrate compliance with the mandatory standard. Specification of a given metric as an output from the calculation leaves no scope for an alternative approach in practice.

Accordingly, change in the definition of the compliance metric may be made without the need to amend regulations, provided said metric remains an energy metric.

Proposal

We do not propose to adopt an energy metric other than delivered energy. Delivered energy is the most direct representation of the overall energy demand of a new building, representing that which must be drawn from external sources to meet the calculated energy demand for the building. We also would not propose to include energy demand from other sources such as cooking and appliances within the compliance calculation.

These elements are not considered to be ‘part of the building’ for regulatory purposes and are only considered in relation to their indirect contribution to space heating and, where onsite generation of power is specified, as an element that can usefully consume generated power, increasing the net utilisation of any generation source present.

Consultation Question 5

Do you agree with the proposal to retain delivered energy, covering only regulated energy use, as the main compliance metric for targets set under standard 6.1 (energy demand)?

Yes

No

Please provide information on why you agree or disagree or if you consider other actions need to be considered.

3.3.4. Secondary energy compliance metrics

The Passivhaus standard includes an absolute target for both space heating demand of not more than 15 kWh/m²/yr or a peak heating load of not more than 10 W/m². This metric drives the delivery of an energy efficient built form and a high level of specification for building fabric. It also relies upon very low fabric infiltration, 0.6 air changes per hour and heat recovery from an efficient MVHR system to contribute to achieving this target. It is reasonable therefore to discuss the potential relevance and benefit of a more formal space heating demand target as part of review of building regulations.

As noted in section 3.3.1, limits on space heating demand are set only through reference to maximum U-values for the planar elements of the building envelope – walls, floors, roofs and openings. Guidance is provided on the benefits of limiting both thermal bridging and fabric infiltration but no prescription is set. The premise being that the performance of such elements must be declared, incorporated in the calculation of the building energy target and will be appropriate for the overall level of thermal performance sought within the design. For new dwellings, the alternative of a space heating demand limit is available. This is also a relative target and reflects the form of the proposed building and the contribution to reducing demand that insulation, infiltration and heat recovery may offer. MVHR systems are discussed separately under section 3.5.

Annual reporting within our Climate Change Monitoring Report references the proportion of new homes in Scotland delivered with a space heating demand of not more than 20 kWh/m²/yr (as calculated by the SAP methodology). As of 2023, this stood at 12.3% of the annual build.

Regulatory relevance

Current levels of expectation for building fabric are defined through the guidance published in support of Standard 6.2 (building insulation envelope).

Should there be support for a move to define a more formal space heating demand target, there is the potential to define this through guidance. This on the basis that the guidance can reasonably be held to define the approach taken to demonstrate compliance with the mandatory standard. Again, specification of a given approach to a performance target would leave little scope for an alternative approach which can demonstrate an equivalent outcome.

Accordingly, any change to introduce a new or more prescriptive compliance metric may be made without the need to amend regulations, provided said metric remains a reportable outcome primarily derived from the performance of the building insulation envelope.

Proposal

Basic compliance with standard 6.2 can be demonstrated simply by not exceeding a set of maximum U-values and by reporting on the calculated performance of building junctions and the infiltration rate of the building envelope within the standard 6.1 energy target compliance calculation. The alternative of the space heating demand limit allows for greater flexibility in the specification of main thermal elements against a relative target which applies notional building values for thermal bridging, infiltration and ventilation solution.

Research currently underway will report on comparative outcomes from the current and proposed UK tool and from PHPP. This will assess the potential benefit of setting a space heating demand target and the form such a target might take, together with any risks which arise from such additional prescription.

Consultation Question 6

Do you support further consideration of the introduction of a prescriptive space heating demand limit for new buildings through building regulations?

Yes

No

If you answered ‘Yes’, please provide information on what form of prescription you would support and the potential benefits and/or risks this may create.

3.3.5. Approach to setting targets – climate data

Building regulations in Scotland currently apply national climate data within the domestic and non-domestic calculation methodologies. As a static element within the calculation of both target and building energy performance this has served the purpose of demonstrating compliance via calculation. However, standardising this data does not enable interaction between the building and its immediate environment to be properly considered, particularly in respect of the energy balance for heating and cooling (where present). This means that the effectiveness of design solutions is not fully considered. Regional climate data is used within the Energy Performance Certificate process, albeit not in the calculation of ratings, but for assessment of the benefit of building improvements.

The proposed Home Energy Model is being developed with the facility to apply regional weather data to all outputs of the calculation process as part of the improvement to data used.

The Passivhaus standard applies approved datasets for regional climate data and location altitude for precisely this reason, to enable representative modelling of the interaction of the building with its surroundings and to enable reporting of an output that is closer to the operation of the building in practice.

Regulatory relevance

Assignment of climate data for new buildings forms part of the calculation methodology. As noted in section 3.2, for the purpose of building regulations compliance, the current methodologies are identified in guidance published in support of standard 6.1.

Accordingly, change in the cited methodologies may be implemented without the need to amend regulations.

Proposal

We intend to adopt the use of regional climate data within compliance calculations to the extent this is practicable and useful. We propose this would be aligned with the current nine regions currently defined for some purposes within the SAP methodology. These same nine regions are identified and used within PHPP. This will provide more representative reporting on the building energy balance and enable more effective decision making by designers.

Use of regional data will result in variance in the reported outcome for a given building in different locations. However, the impact of this is moderated by the application of the same data for both target and building calculation. The impact of regional data is more significant where an absolute target is set, such as is the case for the Passivhaus standard. However, the variance will be investigated and reported upon as part of ongoing research commissioned to support the stage 2 consultation planned for summer 2025.

Consultation Question 7

Do you support the move to application of regional climate data within the approved calculation methodologies and their application within compliance targets?

Yes

No

Please provide information on why you agree or disagree or if you consider other actions need to be considered.

3.4 Building fabric standards

3.4.1. Insulation levels

Building regulations set maximum recommended thermal (‘backstop’) values for elements of the building insulation envelope through guidance to standard 6.2 (building insulation envelope). This defines the general level of expectation in limiting heat loss. That level is set to enable a degree of flexibility in the delivery of cost effective levels of fabric performance that are viable for projects across Scotland.

Due to the use of absolute targets, including for space heating, Passivhaus does not prescribe maximum performance values for building fabric. There is recognition that elements such as triple glazing, with related very low U-values, are expected components and a generally high level of fabric specification and the delivery of close to thermal bridging free design is an expected outcome to both limit space heating demand and deliver thermal comfort.

We will determine the potential for further, deliverable levels of improvement in the specification of building insulation elements as a means of further reducing space heating demand. This issue must be considered alongside the potential to achieve similar effect through other means. The use of targets to promote consideration of energy efficient built form is discussed under section 3.3. The impact of use of heat recovery as part of ventilation is discussed under section 3.5.

A further discussion on how space heating demand is subsequently met, through efficient generation of heat and effective control of heating is also necessary and will be considered in detail within the stage 2 consultation, on guidance to support standards and the defining of updated performance targets, in summer 2025.

Regulatory relevance

Current levels of expectation for building fabric are defined through the guidance published in support of Standard 6.2 (building insulation envelope).

Accordingly, any change to values cited or the introduction of recommended limits may be made without the need to amend regulations.

Proposal

Much on this is discussed under section 3.3.4 ‘Secondary energy compliance metrics’ and the setting of space heating demand targets or limits.

Through commissioned research, we seek to identify where current ‘fabric first’ approaches can readily and consistently deliver building envelopes that offer performance better than the levels currently defined in guidance to standard 6.2. We would also wish to understand how the capacity for further improvement may vary, across building elements, construction types and development situations. And how the cost/benefit of further improvement options may also vary.

Consultation Question 8

Do you currently deliver new buildings that exceed ‘backstop’ values for fabric performance set under standard 6.2 or those used to define the notional building in guidance to standard 6.1?

Yes

No

If you answered ‘Yes’, please provide information on the solutions you apply, any challenges experienced and your views on wider application of such solutions.

3.4.2. Thermal bridging

The limiting of thermal bridging at junctions is important to avoid areas of low internal surface temperatures that can contribute to surface condensation and mould growth, as well as assisting in maintaining a comfortable thermal environment.

Building standards require information to be provided on additional heat loss from thermal bridging at junctions, represented by calculated or default psi (ψ) values, as a component of overall building energy performance. An additional allowance, as a proportion of planar heat loss, is included in the notional building specification for new dwellings (5%) and new non-domestic buildings (default 10%).

Representation of thermal bridging is more rudimentary for new non-domestic buildings than for new dwellings, addressing a reduced range of junction situations and permitting the option of an onerous default value for heat lost through thermal bridging whereas a total heat loss value must be calculated from junction lengths and psi values for new homes.

A similar but more detailed approach is taken within the Passivhaus standard, which seeks to deliver construction which is close to thermal bridge free. The Passivhaus standard also uses external dimensions whilst building regulations use internal dimensions, resulting in a different reported outcome.

Both of the above systems seek calculation to BS EN ISO 10211 and emphasise a managed and informed approach to specification and detailing of achievable construction build-ups and continuity of insulation layers.

Regulatory relevance

Assignment of values for thermal bridging forms part of the calculation methodology. As noted in section 3.2, for the purpose of building regulations compliance, the current methodologies are identified in guidance published in support of standard 6.1. Guidance of limiting thermal bridging, sources of information and how values are to be calculated is provided to support standard 6.2.

Accordingly, any action to amend how this element of specification is defined may be implemented without the need to amend regulations.

Proposal

It remains the intent to reference the UK energy calculation methodologies and, as part of this, the current approach to the calculation and presentation of thermal bridging losses. Current research to support proposals will include reporting on the difference of approach to calculation of psi values between current approved calculation methodologies and PHPP.

The stage 2 consultation in summer 2025 will seek views on this topic and what an appropriate level of assignment of target values might be to encourage a best practice approach for this element of envelope design.

3.4.3. Fabric air infiltration

Building regulations discuss fabric infiltration in the context of both the building fabric specification (standard 6.2) and ventilation (standard 3.14). Whilst noting that reduced levels of infiltration are an effective means of reducing fabric heat loss, guidance does not set an upper limit on infiltration. This is on the basis that this aspect of performance is considered by the building energy calculation and designers may therefore declare a level of performance they consider achievable by their proposed construction solution. The value declared is then checked through testing once constructed. Infiltration is defined by the volume of air that passes through each square metre of building envelope at a given pressure differential, 4 or 50 pascals. The notional building assumes a specified infiltration rate of 5 m³ /(h.m²)@50Pa for dwellings and 4 m³ /(h.m²)@50Pa for non-domestic buildings.

The Passivhaus standard defines a maximum limit for building fabric infiltration of 0.6 air changes per hour when measured at 50 pascals pressure difference. Envelope airtightness is a significant element in the Passivhaus approach, to aid in achieving the target space heating demand through both lower energy loss from leakage and more effective operation of an installed MVHR system. A declared air change rate is always verified by test. As this is an air change rate, it cannot be directly converted to an air permeability rate target by ‘rule of thumb’ but is often described as delivering air permeability at least five times lower than typical new construction to building regulations.

Regulatory relevance

Assignment of a design infiltration rate for new buildings forms part of the calculation methodology. As noted in section 3.2, for the purpose of building regulations compliance, the current methodologies are identified in guidance published in support of standard 6.1. Guidance on considering, defining and testing building infiltration is provided to support standard 6.2. Accordingly, any action to amend how this element of specification is defined may be implemented without the need to amend regulations.

Proposal

As part of the proposal to continue to set a relative energy performance target through the notional building approach, we will continue to specify a value for building infiltration to be used in the calculation of targets. The stage 2 consultation in summer 2025 will seek views on what an appropriate level for this value might be, both generally, or for various building types. We would seek your views on the benefits of greater prescription on fabric infiltration as part of any revised approach to target setting.

Consultation Question 9

Do you have any particular views on limiting fabric infiltration through the building standards?

Yes

No

If you answered ‘Yes’, please provide your views and any supporting information on the benefits and risks arising from greater prescription on this topic.

3.5 Ventilation and occupant comfort

3.5.1. Ventilation and indoor air quality

Standard 3.14 of building regulations requires that ventilation is provided so that air quality inside the building is not a threat to the building or the health of the occupants. The focus being on effective removal of contaminants and provision of replacement air.

Guidance in support of the standard identifies recommended minimum rates of air exchange (domestic) or cites relevant industry codes of practice (non-domestic). A further basic compliance guide for new homes covering selection of systems and delivery through to commissioning is included and last updated in February 2023. The approach to ventilation and system type applied is related to the level of fabric infiltration. Whilst there is a presumption that most new buildings will be designed to lower infiltration rates, all potential approaches are recognised.

The Passivhaus standard differs from this, taking a more prescriptive approach to the delivery of thermal comfort and indoor air quality, through specifying very airtight building fabric and the expectation of a managed mechanical supply and extract ventilation system with heat recovery (MVHR). Aside from reducing space heating demand, such a solution provides greater assurance that expected whole building ventilation rates are achieved in practice.

Standard 3.14 accepts any system/solution for ventilation but does recommend a particular strategy based upon the design infiltration level of the building fabric, also recommending mechanical supply and extract systems for buildings with very low fabric infiltration, below 3 m³ /(h.m²)@50Pa.

Fabric infiltration is discussed in section 3.4.3. MVHR as a building solution and ongoing topic of interest is discussed under section 3.5.2.

Regulatory relevance

Standard 3.14 (ventilation), as written, seeks to deliver a general outcome. The standard is reliant upon supporting guidance to define both the level of performance sought and to provide examples of means of achieving that performance. Guidance again setting out common means of achieving compliance.

Guidance on defining and delivering adequate building ventilation is provided to support standard 3.14. Accordingly, any action to amend how this element of specification is defined may be implemented without the need to amend regulations.

Proposal

Research published last year on domestic and non-domestic ventilation highlighted a number of areas where further review of standards and associated provisions may be beneficial.

Work is underway in parallel with this review to investigate what level of assurance around effectiveness in use can reasonably be asserted for various ventilation solutions and how this is affected by the design, installation and commissioning process. This will consider, amongst other topics, the general trend towards lower infiltration in new buildings and how to identify and address the key risks at both design and construction phases for different solutions.

Alongside current research on improvements to energy standards, this will inform proposals put forward for consultation in summer 2025. We would seek your views on the benefits of greater prescription on fabric infiltration as part of any revised approach to target setting.

Consultation Question 10

Do you have any particular views on the means by which effective ventilation of new buildings is best achieved?

Yes

No

If you answered ‘Yes’, please provide your views and any supporting information on the benefits and risks identified in the delivery of your projects.

3.5.2. Mechanical Ventilation with Heat Recovery

Guidance in support of the standard 3.14 (ventilation) identifies recommended minimum rates of air exchange (domestic) or cites relevant industry codes of practice (non-domestic). This section focusses primarily on consideration of MVHR as a component of new dwellings.

Current building regulations do not set prescription on the approach to ventilation to be used in new buildings but do refer designers to the need to consider fabric infiltration as a factor when determining an appropriate ventilation system. For example, recommending the use of continuous mechanical supply and extract in new homes with a proposed design infiltration rate below a certain limit. The optional space heating design limit available for new homes under standard 6.2 (building insulation envelope) also considers the benefit that ventilation with heat recovery offers in reducing the space heating demand a heating system is required to meet.

The Passivhaus standard has a strong focus on effective action to reduce heat demand and, whilst not a prescribed solution, it is considered impractical to achieve the defined space heating demand target without the use of efficient MVHR. In effect, the design and installation of effective MVHR is a signature element in Passivhaus buildings.

In the development of the current review, the benefits of MVHR have been clearly identified in many discussions with stakeholders. A well designed and installed system will both reduce space heating demand and provide more assurance on the delivery of good indoor air quality through levels of input air supply which are verifiable as part of system commissioning. Such systems can also operate in bypass mode, to support effective evening or night-time cooling during summer months.

In parallel, some concerns have been raised over challenges associated with the ongoing operation of such systems including increased reliance on mechanical systems, user intervention and the need to maintain the system (specifically replacing filters).

The introduction of efficient heat recovery system to a well-insulated building with low fabric infiltration can offer greater benefit than further enhancements to the building fabric specification and may often offer a more cost effective means of improving overall performance.

Regulatory relevance

Examples of the approach taken in achieving compliance with standard 3.14 are set out in supporting guidance which covers levels of ventilation sought and the characteristics of systems and solutions. Similarly, achieving overall energy targets defined under standard 6.1 (energy demand) currently enables designers to achieve an overall outcome by whichever route they determine as most appropriate for a given development. The outcome (target delivered energy rate) is, however, defined by a notional building specification that sets out an illustration of a balanced approach to the specification and components of a new building. Currently, MVHR is not part of this specification.

Accordingly, change in the cited solutions may be implemented without the need to amend regulations. An exception would only arise if a case was made to mandate a specific single solution to the standard, which is considered very unlikely on such a topic.

Proposal

In the context of the ongoing focus to optimise the energy performance of new buildings, heat recovery is a design option which should be properly considered at an early stage of a project. This makes heat recovery as part of ventilation an element of specification to consider in the same way as other elements of energy-relevant specification which can offer multiple benefits.

Work, separate from this current review, is planned for 2024 to investigate and assess the levels of assurance that can reasonably achieved by a range of ventilation solutions. It is already recognised that use of both mechanical supply and extract can eliminate much of the variation in ventilation performance associated with a reliance on passive background ventilators.

MVHR has benefits, particularly for more airtight and energy efficient buildings. However, mandating its use is at odds with the approach of building standards that allow designers to meet the regulations in more than one way. We are seeking your views on the role guidance should take for MVHR in new construction. For example:

• Is there a strong case to reference the use of MVHR within any revision of the Technical Handbooks?
• Is such action more useful than simply considering further enhancements to insulation standards?
• Should communication on a ‘fabric first’ approach move towards a stronger emphasis on the linking of fabric and services strategies, as already well embedded within the Passivhaus standard?

Consultation Question 11

Specifically for new homes should further guidance be given on MVHR, generally, and through the Technical Handbooks?

Yes

No

If you answered ‘Yes’, please describe what approach to this work you consider would be most appropriate in driving forward informed, good practice on both energy and ventilation performance.

3.5.3. Overheating Risk

Both building regulations and the Passivhaus standard include a requirement to assess the risk of peak summer overheating and take action to limit that to reasonable levels.

Standard 3.28 (Overheating risk) requires that a new dwelling (or similar non-domestic residential buildings) be designed and constructed in such a way that the risk to the health of the occupants from overheating is reduced. Supporting guidance offers two approaches to satisfy the standard - a simple approach which limits heat gain through glazing and seeks adequate purge ventilation and a detailed thermal modelling approach using a recognised methodology, CIBSE TM59. Both approaches are applied on a room-by-room basis.

The Passivhaus standard applies a whole building assessment, undertaken within the PHPP calculation. This approach sits between the two options set out under standard 3.28. Both approaches seek to address the issue via passive cooling where practicable.

No updating of the current provisions under standard 3.28 are proposed as part of this review. Such work will be commissioned separately. It is noted that should Passivhaus certification be recognised as an alternative means of compliance (see section 3.6) then, subject to confirmation of the comparative efficacy of the whole building approach, reference to the PHPP overheating assessment could be identified in guidance as a third means of satisfying standard 3.28.

3.5.4. Occupant comfort

A range of issues need to be managed in the design and delivery of a building to offer good levels of occupant comfort. This includes solar gain and overheating risk, air quality and movement, temperature levels and differentials and environmental noise.

Both building standards and the Passivhaus standard address a range of such issues in broadly similar ways. For example, a relatively uniform and consistent approach to the building insulation envelope, minimum expected ventilation rates, assessment and mitigation of overheating risk, and guidance on noise from installed systems such as ventilation.

In this respect, the Passivhaus standard sets out a strong, design-led approach to deliver high levels of occupant comfort, carried through to the verification of the design to construction and commissioning. Optimising building form and layout for useful solar gain whilst avoiding overheating risk, a high and consistent specification for building fabric, assurance on air quality through effective use of mechanical systems and assessment of surface temperatures and services noise.

There has not been a significant focus on occupant comfort as a specific topic within review discussions to date. It is recognised that current provisions in building standards and Passivhaus standards do differ and that greater assurance on this topic is likely to be gained from a more informed and evidence led approach to design and construction through building regulations. This is discussed in Section 4, which also highlights some examples of performance issues which can be detrimental to occupant comfort, such as inconsistency in the delivery of the thermal envelope.

Consultation Question 12

Are there areas of newbuild design and specification you would wish to highlight as potential risks to occupant comfort that should be better addressed through the building standards?

Yes

No

If you answered ‘Yes’, please provide examples of the issues encountered and, where available, the solutions employed to address the problem.

3.6 Alternative means of compliance

3.6.1. Passivhaus certification

Both building regulation and the Passivhaus standard define and seek to deliver a series of outcomes, including overall energy performance targets and minimum levels of elemental performance. For building design, key elements in both processes are discussed earlier in this section of the consultation.

Since 2007, building regulations have set energy or emission targets for new buildings, demonstrated under the UK calculation methodology SAP or SBEM. From April 2024, with the introduction of the New Build Heat Standard, the only target set is an energy demand target under standard 6.1 (energy demand).

This standard is the closest analogue to the Passivhaus standard space heating demand and energy use intensity limits, with outcomes calculated via PHPP. Passivhaus cites an absolute value, targets set under building regulations are currently relative, based upon a notional building defined in guidance. Building standards do cite such absolute values but only in supporting guidance for the voluntary aspects of standard 7.1 (statement of sustainability), for Aspect 2 (Useful energy for space heating).

The calculated outcomes for a given building form and specification also differ between approved methodologies and PHPP. There have been studies which identify and comment on these differences and research underway, in support of this review, will also consider and present information on where and why these occur. However, it can be established that with only potentially minor exceptions, a new building designed to achieve Passivhaus certification will achieve reported outcomes that improve on those sought by building regulations. This presents a strong case to consider Passivhaus certification as an alternative to current target setting process under standard 6.1, without the need to provide a comparative calculation assessment to demonstrate the extent to which “it is capable of reducing the energy demand of the building”.

Regulatory relevance

Should there be a recommendation to formally recognise Passivhaus certification as a means of demonstrating compliance with one or more relevant standards, regulatory change would depend upon the nature of the standard in question and the extent to which output from the Passivhaus certification process was used for verification purposes.

Where sufficient information to enable verification against current standards is present, then citation may simply not be necessary as compliance may be demonstrated by the current route, as further enhanced by the proposals to improve compliance, set out in principle within Part 4 of this consultation.

An exception would be standard 6.1 (energy demand) where the compatibility of the respective approaches to target setting and the metrics defined would make citation complex.

However, there is the option for citation without the need for a comparison in calculated outputs. As standard 6.1 sets a requirement that energy performance is calculated using an approved methodology of calculation, referencing approval under other (energy performance certificate) legislation, the most direct means of recognising an alternative would be to define a further limitation to the standard. Such a limitation would define the criteria for exemption. For example, confirmation by a Passivhaus certifier that a submitted design meets the design requirements of the Passivhaus standard.

Accordingly, formal recognition of Passivhaus certification as an alternative means of compliance would most likely result in the need to amend regulations.

Proposal

Subject to the conclusion of current research to evaluate the differential in reporting between calculation methodologies, we would propose that confirmation of design-stage compliance with the Passivhaus standard be considered as an alternative compliance solution. In parallel with this consultation, we will determine the procedure that would be applied to enable Passivhaus certification, as an end-to-end process, to be identified as an alternative means of complying with standard 6.1 (energy demand). A comparative calculation using the cited domestic or non-domestic methodology would not be required to be submitted to prove compliance.

Beyond the position set out above, we would welcome your views on the extent to which Passivhaus certification could be recognised as delivering an alternative means of compliance to specific standards.

Note also that compliance benefits achievable though Passivhaus certification are discussed under section 4.

Consultation Question 13

Do you consider that Passivhaus Certification offers a feasible alternative means of compliance with standard 6.1 (energy demand)?

Yes

No

Please provide information on why you agree, or disagree and on the extents to which this alternative might be usefully applied in practice.

3.6.2. Alternative verification – Certifiers of Design

Building standards in Scotland offer an alternative means of confirming that the design of building work which is the subject of a building warrant complies with specified mandatory standards. Individuals can be appointed as an Approved Certifier of Design and can certify compliance within the scope of their registration, removing the need for the local authority verifier to undertake a detailed check on such elements prior to granting a Building Warrant. Each Approved Certifier must also be or be supported by an Approved Body, who provides resource and indemnity for their certification activity.

The Certification process is managed through Scheme Providers, organisations approved by Scottish Minister to manage and audit the activity of registered certifiers through their Approved Bodies. Information on this optional process can be found in the published Certification Handbook.

There is currently a Certification of design scheme for section 6 (energy). Current Scheme Providers are part of the review working group. This is assisting in the consideration of potential implications for the current certification regime, from this review and also in the context of the broader proposed changes to compliance processes (see section 4).

3.7 Summary of proposals

In setting provisions for the design and specification of new buildings, we propose to develop standards on the following basis and seek your views on:

• Continued use of the UK calculation methodologies, as updated, and to implement the proposed updates to both domestic and non-domestic methodologies.
• The benefits of defining absolute targets for aspects of building performance but propose to continue to set relative targets for the overall energy performance of new buildings.
• The case for defining a space heating target for both new dwellings and new non-domestic buildings and the form this might take.
• Supporting effective decision making in design choices and making outputs more representative, by adopting the use of regional climate data within calculations to the extent this is practicable.
• Based upon current good practice, considering what further opportunities arise to set more challenging provisions for fabric insulation.
• The benefits of an informed approach to the definition and delivery of a low infiltration building envelope.
• The means by which the benefits of effective MVHR systems can be more broadly represented within standards.
• The recognition of Passivhaus certification as an alternative means of complying with standard 6.1 (energy demand).

Provisions relating to assurance on compliance are addressed in section 4.

To emphasise – these are proposals and information is provided to set out the reason for the initial approach described. We seek your views and evidence on whether or not these will, collectively, define a robust approach for the development and delivery of revised provisions. The extent and detail of those provisions will then be set out in the Stage 2 consultation next year.

Consultation Question 14

Are there any other comments or observations you wish to make on the proposed components of the review which relate to building design?

Yes

No

If you answered ‘Yes’, please provide your further comments or observations. Additional supporting information may also be provided by attaching a separate document to your response.