Differences between ratings for EPCs in Scotland and England

Prelude

EPCs in Scotland and England should not be directly compared because of the different calculation basis that are been used to generate a result. By way of background, the calculation engine behind non-domestic EPCs is SBEM.EPC ratings in Scotland
The different calculation methodology used in Scotland the rest of the UK is not helpful. The different system have led to confusion as the grades achieved may appear very different.

Conclusion

In order to compare the energy efficiency of buildings in England and Scotland more information needs to be considered than just the headline rating achieved. Often ratings in Scotland are poorer than a similar building would acheive and this cannot be attributed to weather factors. A building in England will appear to be more energy efficient than that same building in Scotland and this may cause investors to favour investment bias towards England.

English and Scottish EPC rating systems

The Scottish EPC rating system calculates the numeric asset rating as the BER (Building Emissions Rate) in kgCO2/m2/yr, and the associated band is derived from a linear carbon scale A-G from 0 to 100. An advantage of this is that it is transparent.English EPC ratings
The EPC system in England & Wales however calculates the asset rating based on a ratio of the BER and SER (Standard Emission Rate). The SER emissions of the reference building with a fixed improvement factor is multiplied by 50, and the associated band is derived from a self reference linear scale where the B-C boundary is fixed at 50 and the top of A is 0. The upper limit for the English rating system is 150 but it should be remembered that this is not a linear carbon scale as per the Scottish system.

Case Study

As a basic example of the different rating an English and Scottish EPC can give we compared the rating of an actual EPC for a standalone modular retail unit we recently carried out an EPC for. The unit benefits from a new high efficiency split system (utilising air source heat pump technology) and T5 lighting. All specific building and efficiency data is available including the actual air infiltration rate based on a tes, lighting design data, specific fan power and DHW heat losses. The calculation was re-run with the building location being in Scotland and then England. As above the calculation method will be different and the results are as follows:

Region Rating
Scottish EPC
English EPC B
EPC Regional Differences


 

 

 

 

 

Looking Closer

If the energy efficiency grade of the buildings were compared it would appear that the English building was far more energy efficient than the Scottish building. This is not the case however. If the BER of the English EPC (located at the foot of the first page) was compared then the comparison would be more representative.

Further consideration

It has already been mentioned that comparisons on the numeric rating between the Scottish and England & Wales approach are inappropriate. However, it might be difficult to avoid users comparing A-G bands obtained for similar buildings with the two approaches. It appears that for similar levels of performance the band parameter is quite different between the two approaches. While the England & Wales approach, based on a self-reference scale, tends to return wide band ranges for wide energy performance ranges, the Scottish approach, based on absolute carbon and the current limits within the bands, produces a reduced range of bands for wide performance ranges in certain sectors

It could be argued that the relative rating used in the England & Wales approach is difficult to understand, and that the absolute carbon figure used in the Scottish approach is much clearer.

Focusing on the rating parameter within the EPC systems, the Scottish approach offers a much clearer indication of the energy (and carbon) performance of the buildings.

However, it could also be argued that the band assignment system within the England & Wales approach tends to spread wide ranges of building performances over the whole scale, while the absolute scale used in the Scottish approach is much less sensitive for certain building sectors in the assignments of EPC bands.

A lack of understanding of the principles behind this approach and how they compare with the self-reference method may be causing these perceived disadvantages between the EPC calculation method used in Scotland, when compared to that used in England and Wales.

If you are really interested then further information is available from a Scottish Government report with a full version is available here.