Building regulations 2025 - new non-domestic buildings: energy standard improvements - modelling report
Research output to identify and assess potential improvements in energy and emissions performance for non-domestic buildings constructed in Scotland set via Section 6 of the Scottish Building Standards (energy). This was to inform the setting of targets within the next set of energy standards.
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Executive Summary
The aim of this project was to identify and assess potential improvements in energy and emissions performance for non-domestic buildings constructed in Scotland set via Section 6 of the Scottish Building Standards (energy). This was to inform the setting of targets within the next set of energy standards, programmed for implementation in 2028.
Impact of potential improvements to the notional building
Potential improvements to the current notional (reference) building were identified based on a review of current practice for new constructions in Scotland and other relevant literature. Three new alternative standards (“Low”, “Medium” and “High”) were developed. The EPC database for all newly constructed buildings from January 2021 to September 2024 was analysed for indications of what building specifications are currently typical practice (“low” based on the 50th percentile), good practice (“medium” based on the 75th percentile) and best practice (“high” based on the 90th percentile). Their benefits and costs were assessed at an individual building and national level. This analysis indicated that the current typical practice (“low”) is generally closely aligned to the current notional building specification and so broadly matches the current Section 6 standards, i.e. current typical practice does not go beyond the current standard. In comparison, the “medium” and “high” scenarios do model significant improvement beyond current typical practice (“low”).
Following a ‘fabric first’ approach, the performance of the building envelope was first considered for improvement. It was found that there was little evidence to support significant improvement in this area, and so all three options adopt the same fabric standard as the current standard in most areas. The principal exception to this is the inclusion of triple glazing for the “high” option. The “low” scenario differs from the current notional building to align with typical practice in terms of lower performance in air tightness, whilst the “medium” and “high” scenarios include improvements in air tightness.
After adopting building fabric improvements to reduce building energy demand, other measures were included to reduce the building’s energy consumption. Notably, the “medium” and “high” scenarios include improvements in heating, cooling and lighting efficiencies as well as an increase in the amount of solar PV compared to the “low” scenario. To reflect current practice as demonstrated in the EPC database, the “low” scenario uses a lower cooling efficiency and higher performance in heat generator efficiencies compared to the current Section 6 notional building.
For all three options, it is proposed that the notional building is based on fossil-free heating plus PV with an increase in the array size compared to the current notional building. This would simplify the current approach where the extent of the PV depends on the heat source(s) in the actual building.
The “Low”, “Medium” and “High” options are estimated to reduce carbon emissions by -0.7%, 10.1% and 11.4% respectively across the build mix. This was evaluated using SBEM v6.1e and the proposed new carbon emission factors, across 11 building archetypes.
It is estimated that the capital costs of solutions typically range from -1% (lower) for the “Low” option to +11% (higher) for the “High” option than the current standard across the different building types and the three alternative standards.
The national cost benefit analysis shows that the “Low” option results in a benefit of £2m whilst the “Medium” and “High” options result in a net cost of £33m and £330m respectively.
Differences between modelling in SBEM and PHPP
Further analysis of the same building specifications as modelled in SBEM v6.1e was undertaken in Passivhaus Planning Package (PHPP), to understand how modelled building performance may differ between PHPP and SBEM. PHPP uses different building physics algorithms and requires significantly more detailed data inputs than SBEM. Therefore, if this were to be adopted as an alternative compliance calculation method, a decision on the level of data entry would be required.
The analysis demonstrates that the results from the PHPP models show a close enough alignment with SBEM to predict a similar level of impact for individual and groups of specification changes when an aligned modelling approach is used (that is, tailoring the PHPP inputs to match as closely as possible to the SBEM inputs). Further work would be required to confirm that models using full PHPP conventions show a similar level of agreement to SBEM models.
Investigations into additional targets
Alongside consideration of an improved building specification, the analysis considered where the notional building target setting methodology may not sufficiently reward energy efficient design. In particular, the lack of incentive for improved efficiency through adjustments to built form and shape, as the notional building dimensions are the same as the actual building dimensions.
Our view is that to introduce an incentive for built form would be complicated to implement successfully. Further research would be necessary to assess and develop such an approach in a robust and fair way across a wide range of non-domestic building types and avoiding unintended consequences or loop-holes.
In addition, the rationale for introducing a space heating demand limit was evaluated, and whether this should have primacy over the current Target Delivered Energy Rate. It was determined that while delivered energy and space heating demand correlated, the extent significantly depended on building type and system configuration. Our analysis has identified two key challenges with adopting a space heating demand limit as the primary compliance metric.
1. For certain typologies and based on the NCM gains, the BAU specification can comply with an absolute space heating demand limit of 15kWh/m².yr (as per LETI and Passivhaus guidance). Whereas, for many of the building types assessed, an absolute limit of 15kWh/m²/yr would be extremely challenging to achieve.
It will be for the Scottish Government to consider whether a single space heating demand target applicable to all building types would be appropriate. An alternative is that the target could be varied between building types such that they are more similarly challenged.
2. Should a space heating target be adopted as the primary compliance metric, this may not drive improvements in other energy end uses that are not impacted by fabric performance, such as lighting or domestic hot water, which can dominate the overall building energy demands for some building types. Hence, there would still be the need for an additional metric to drive broader improvements.