Building regulations - proposed changes to energy and environmental standards: stage 2 consultation and BRIA

4 Secondary compliance metric – space heating demand

4.1 Introduction

Standard 6.1 ‘Energy demand’ allows flexibility in building design by enabling a whole-building approach to meeting a single energy target. To help maintain a high standard across all parts of the building envelope, the use of elemental backstop values or space-heating demand limits offers designers reasonable flexibility while still ensuring good overall energy performance.

Under SAP 10, the approach previously used relies on a calculation commonly known as the “box 99” space-heating demand. This calculation takes account of both fabric performance and the reduction in heat loss achieved through ventilation heat-recovery where Mechanical Ventilation with Heat Recovery (MVHR) is installed. While this metric shows the energy savings gained from heat recovery in reducing space-heating demand, it can also allow poorer fabric performance to be offset by the inclusion of an active mechanical ventilation system.

By contrast, the Passivhaus standard sets a clear and absolute limit for space-heating demand of no more than 15 kWh/m²/year. This requirement strongly encourages an energy-efficient building form and a very high standard of fabric performance. Achieving this target also depends on extremely low air infiltration and the use of an efficient MVHR system to recover heat from ventilation losses.

The Scottish Government’s Climate Change Plan Monitoring Report tracks the proportion of new homes with a space-heating demand of no more than 20 kWh/m²/year, as calculated using SAP. As of May 2025, this accounted for 15.9% of annual housing completions. In addition, Standard 7.1 ‘Statement of Sustainability’ sets space-heating demand targets to achieve optional upper levels of sustainability: 30 - 40 kWh/m²/year for houses and 20 - 30 kWh/m²/year for flats or maisonettes, calculated using the SAP 10 box 99 method.

4.2 Proposals

Given the response to proposals within the July 2024 stage one consultation (88% of all respondents supporting further consideration of the introduction of a space heating demand limit). We propose that compliance with standard 6.2 ‘Building insulation envelope’ should now go beyond demonstrating exceeding a set of maximum U-values and 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.

For all new buildings this will be via the introduction of a target space heating rate as calculated using the Home Energy Model / Scottish ‘Wrapper’ for new dwellings and SBEM for new non-domestic buildings, set at a level of challenge indicated in sections 5.1 and 6.1 for new dwellings and new non-domestic buildings respectively.

We propose that this target space heating rate will only include elements of the specification related to the fabric and not take the benefit of active services systems into account.

Consultation Question 5

Do you agree with the proposal to introduce a target space heating rate that only includes elements of the specification related to the fabric performance?

Yes

No

Please provide a summary of the reason(s) for your view.