On 1st October this year, the Scottish Government will implement the next step in its move towards near net zero carbon buildings. The biggest changes are for new domestic and non-domestic buildings and these once again make the performance of the building fabric a central concern for architects, Kingspan Insulation writes
New domestic buildings
In line with the findings of the government consultation, Section 6 2015 requires a further 21 per cent reduction in carbon emissions over the previous standards. As with the 2013 Domestic Technical Handbook, there are two routes to compliance for new domestic buildings. A simplified approach requires dwellings to meet all of the criteria set out within a space heating fuel table, which includes tightened building fabric requirements shown in Figure 1. However, only limited deviations are allowed from the specification and costly renewables may be required dependent upon main heating fuel. The whole dwelling approach provides greater flexibility. A Target Emission Rate (TER) is calculated based on a ‘notional dwelling’ of the same size and shape as the actual building. A Dwelling Emission Rate (DER) is then calculated for the property and must not exceed the TER. Both of these calculations will be carried out using SAP 2012. To ensure that a high level of thermal performance is achieved as part of any dwelling, the area weighted maximum U-values have also been lowered (Figure 2). By attaining the best possible U-values it is possible to limit the use of renewables and relax some of the more stringent notional dwelling requirements. Kingspan Insulation has analysed the options and provided recommended building fabric U-values in Figure 3. These will be a little more than is required for some buildings and a little less for others, but provide a good starting point for the majority of applications.
New non-domestic buildings
The change for new non-domestic properties is even greater with a 43 per cent uplift over the previous carbon emission requirements. As with Section 6 2013, the National Calculation Methodology (NCM) is used within an approved tool, typically SBEM, to create a notional building from which a TER is generated. In addition to improving the building fabric performance values for the notional building, the new Standards also allow heated buildings to be separated into zones depending on whether they are naturally or mechanically ventilated. A Building Emission Rate (BER) is then created based on calculated performance against the notional building. The actual specification can vary from the notional, provided the calculated BER is better than the TER and the limiting requirements are met. Fabric performance is strongly supported with tightened area weighted average U-values, particularly for shell buildings. Again, a recommended starting point for a fabric first approach for non-domestic buildings is provided in figure 4.
Getting the fundamentals right
Despite the varying requirements in Scotland, England and Wales; there is a clear consensus that a fabric-first approach should be prioritised over reliance on bolt-on renewables. By specifying high performance insulation and paying close attention to detailing, this approach should provide consistent results and ultimately deliver strong long-term energy savings for the building owner.
