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

Research to identify potential improvements in energy and emissions performance for new domestic buildings. Produced in support of proposed improvements to energy standards for new buildings within Scottish building regulations in 2021.


1. Data was excluded where certificates were pre-2016 (19 records, of total provided by Scottish Government), where the fields 'Part 1 Construction Year/Age Band' were pre-2014 (1754 records, including many likely relating to conversions of buildings), or where the average wall U-value was greater than or equal to 0.6 (95 records. These cases were all also missing airtightness test data and most also had poor performance elsewhere e.g. single glazing).

2. Likely to be based on storage heaters, as the second most common main electric heating type in the database extract (after ASHP) was electric storage heaters (around 15% of electric-heated homes).

3. Air permeability rates were also included in the database. Analysis of these two fields in combination showed that only around 3% of all records had both 'mechanical, supply and extract' selected and air permeability rates of under 4 (in this case, it could reasonably be assumed that MVHR is being specified). This low figure was somewhat surprising, but as noted above feedback from developers in Scotland confirmed that MVHR was not commonly specified in new build Scottish homes.

4. Data suggests that over 80% of new build homes in Scotland have a timber frame (for example NHBC, Housing Market Report No. 298,July 2017, Table QS15).


6. Looking at 2018 registrations only for all specification was considered, but this was not found to make a significant difference to U-values, for example.

7. This is understood to include district heat networks supplied by renewable heat (PEF = 0 applied to renewable portion). It does not include biomass and biofuels which have a PEF = 1 applied plus adjustments for processing energy. BRE have confirmed that this is because such fuels are not considered to be on-site renewable fuels, as the energy is not created on site and it could have been used elsewhere in the economy. This will have implications for biomass-heated homes where currently targets are based on CEFs which are close to zero (though the use of a concurrent 2015 notional building differentiated by heating fuel and based on biomass in Scotland will mean that the change is less significant here than in other UK administrations, as biomass-heated homes already have to meet stricter targets).

8. These renewable electricity factors inform others above.

9. In cases where the notional is defined as being the same as the actual building, this can allow more flexibility in compliance and can help avoid situations where developments are penalised or rewarded for variables largely determined by factors which may not relate to energy performance alone and may be outside of their control – or which may have a more complicated relationship with energy performance meaning that they impact positively or negatively in different circumstances. However, this flexibility needs to be balanced with consideration of encouraging good energy performance.

10. Note that the Section 7 targets may need reviewing/checking to align with improvements made to Section 6 standards, and to see how changes in the methodology in SAP 10.1 may affect the figures (see Table 1.5o for a summary of relevant changes). This is outside of the scope of the current study, but the space heating demands of modelled buildings will be reported upon.

11. Note that in SAP 10.1 it is proposed that energy savings from increased airtightness in naturally ventilated buildings are now no longer assumed to accrue below air permeability rates of 3m³/m²/h; this change formed part of the England Part F 2020 consultation.

12. To help ensure these benefits to occupants are realised, a respondent suggested that "new build flats solar installations could be connected to individual flats to ensure that generation could be consumed locally instead of being exported back to the grid to benefit of the landlord."

13. A respondent suggested that "As electricity demands increase [e.g. due to EVs], new homes must be capable of generating a minimum of 30% of their consumption if not as much energy as they use."

14. One respondent additionally noted that the 2015 notional building fabric standards are similar to the 'full FEES' scenario previously proposed by the Zero Carbon Hub.

15. Note that currently this reduction is calculated based on SAP 2012 carbon emission factors.

16. It should be noted however that the specifications modelled for the 45% reduction scenario were significantly different from those in the 2015 notional building (and in the 2015 compliant buildings used for the current research); for example typically including MVHR, with solar thermal in some cases, and improved thermal bridging – PV was usually only added/substituted for solar thermal in the 60% reduction cases. It is unclear from the report why MVHR was specified in preference to PV, for example, though the report refers to providing "typical cost-effective example[s]" of improvement specifications; this perhaps relates to different ways of defining cost-effectiveness.

17. This will particularly affect heat pumps, and also solar PV. For PV savings in primary energy for the same packages would be reduced due to the lower factors, in particular depending on assumptions about grid export/use of generated energy on-site. For heat pumps, overall primary energy would significantly reduce due to the lower factors.

18. This might particularly affect technologies which have historically been less commonly specified, though learning rates were applied in the analysis.

19. Homes were selected for monitoring only where they most closely approached meeting Part F 2010 guidance.

20. It was noted that this issue would be expected to increase as buildings become more airtight, reducing general infiltration and increasing reliance on trickle ventilation.

21. This is intended to reflect that for more airtight homes the design, sizing and positioning of ventilators is more critical and that suitable expert advice should be obtained instead.

22. This is somewhat similar to a recent report for Scottish Government which noted the risks of increased airtightness impacting adversely on indoor air quality, but referenced research suggesting that better and correctly used ventilation should mitigate these risks (Aether, 2017).

23. On the other hand, other research has also highlighted mid- and top-floor flats as being particularly at risk where sufficient ventilation and protection from heating by the sun is lacking (Committee on Climate Change, 2017).

24. Mean internal temperature exceedance of 25°C for more than 10% of the year (based on annual rather than occupied hours), though a 4% limit is seen as preferable. It should be noted that findings on overheating using this check did not always correspond well with occupant feedback, which the authors suggest may relate to different occupant expectations relating to comfort.

25. It also noted concerns with MHVR and cited research suggesting natural ventilation strategies may be preferable in terms of impact on both thermal comfort and indoor air quality.

26. Cold-related winter deaths however are projected to continue to be more significant though on a downwards trend (Climate Exchange, 2016).

27. It should be noted that savings would differ should an alternative baseline heating fuel/system be assumed. For example, if a more efficient heating system such as a heat pump was assumed, savings for energy efficiency measures would be relatively less – however such savings might be worth more in terms of energy costs per unit of energy saved (as electricity prices are higher than gas prices). There would also be a different profile in terms of primary energy/carbon emission savings due to different primary energy and carbon emission factors for different fuels. There are also interactions between some measures – for example fabric efficiency would impact on heat pump sizing and performance.

28. By contrast in the CCC's research the same space heating demand level was targeted for each dwelling type and the fabric specification varied for each type to reflect the relative efficiency of their form factor.

29. Currie & Brown's cost management team are currently delivering a wide range of projects across the whole of Scotland including for both housing associations and private developers.

30. Oil has higher primary energy and carbon emission factors than LPG, so if oil-heated homes complied with potential targets given a certain specification then it would be expected that LPG-heated homes would too, but with the potential for relaxation in the specification.

31. The case can be seen as an example of an existing heat network which is being expanded for new homes to connect. It could be expected that there will be greater encouragement for future new heat networks to adopt lower carbon heat sources.

32. Performance data sourced from recent energy from waste CHP assessment for a power led plant providing 14.3MWth average heat output and 66.1MWe average power export.

33. The NHBCF calculations excluded party walls from the calculation (and possibly also semi-exposed walls, though this is not clear from the report). If form factor was to be assessed in order to inform modifications to notional building targets, there might be a question of whether party walls should be included given that there can be heat loss associated with these walls. However, this would not be expected to substantially change the findings observed in the current report. In the current analysis, semi-exposed walls were included in the form factor calculations.

34. Unless consistent floor areas were being compared across dwelling types, the relationship would also be different if space heating demands were looked at in terms of per square metre of floor area as opposed to total annual demands.

35. Valuation of energy use and greenhouse gas emissions for appraisal (April 2019)

36. Costs increases may be outside the described range for highly bespoke designs, however these homes are typically more expensive to build and so the relative impact on build costs may be similar or potentially smaller than for more typical homes built in higher volumes.



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