Building regulations - new domestic buildings - modelling of proposed energy improvements: research report

Executive Summary

1. The aim of this project was to assess and identify potential improvements in energy and emissions performance for new domestic and non-domestic buildings constructed in Scotland set via Standard 6.1 (carbon dioxide emissions). This was to inform the setting of targets within the next set of energy standards, programmed for implementation in 2021. This report focuses on the project findings for new domestic buildings.

2. Improvements to the current notional (reference) building were identified based on a review of current practice in Scotland and other relevant literature. The relative cost-effectiveness and feasibility of these improved measures were assessed. Based on this, two new alternative standards ("Option 1" and "Option 2") were proposed. Their benefits and costs were assessed at an individual building and national level.

3. Option 1 comprises improvements to the fabric efficiency of the notional building and the inclusion of waste water heat recovery. Option 2 includes further improvements, including triple glazing and the adoption of mechanical ventilation with heat recovery. Developers can build to alternative specifications as long as they meet, or improve upon, the performance of the notional building.

4. For both options, it is proposed that the notional building is based on gas heating plus photovoltaics (PV), with typically an increase in the array size compared to the current notional building. An exception is proposed if a heat pump is used in the actual building, where an air source heat pump (ASHP) is included and the PV element removed in the notional building. This would simplify the current approach where the fuel in the notional building depends on that included in the actual building. This is to help avoid heat pumps being able to meet the gas heating targets with relaxation in other elements of specification, including fabric energy efficiency.

5. Options 1 and 2 are estimated to reduce carbon emissions by 32% and 57% respectively across the build mix. This was evaluated using the SAP 10.1 methodology, including SAP 10.1 carbon emission factors, across 7 building archetypes, based upon current build levels and fuel mix in Scotland. This compares to a recommendation in the 2007 Sullivan Report to achieve aggregate emission reductions equating to at least 27.5% on 2015 standards.

6. It is estimated that Options 1 and 2 for a semi-detached home, as an example, will increase the capital costs by 4% and 7% respectively if gas heating plus PV is used. This cost is reduced if ASHP is used, increasing the capital cost by 3% and 6% respectively, providing encouragement to lower carbon fuels. In general, it is estimated that the capital cost is lower for an ASHP for individual homes but higher for flats.

7. The national cost benefit analysis shows that Option 1 results in a net benefit of £46m whilst Option 2 results in a net cost of £250m. This difference is driven by the incremental capital, renewal and maintenance costs for Option 2 being nearly double those for Option 1 and this negates the greater savings in energy use from Option 1.

8. The Scottish Government proposes that primary energy becomes the main target metric. This analysis demonstrated the benefit in retaining the carbon dioxide equivalent emissions target as an additional metric to encourage a move to lower carbon fuels.