5 Using SAP and EPC Data
5.1 Under the Energy Performance of Buildings (Scotland) Regulations 2008, landlords are required to provide a copy of a valid EPC to any prospective tenant. An EPC is valid for a period of ten years from the date of issue. This means that EPC data will be available for an increasing proportion of social housing stock, but not for all stock and not necessarily in the most recent iteration of SAP. Landlords are not required to obtain additional current EPCs for all their housing stock, nor are they required to obtain a new EPC after completing energy efficiency improvements. However, they should be satisfied that they can calculate or estimate the current SAP rating for the property, and they may opt to obtain an EPC in order to demonstrate the current rating when a house is re-let.
5.2 Landlords should model the energy performance of all applicable housing in their stock. This should include the following sources of data:
- EPC data where this is available;
- SAP calculations made to evaluate energy efficiency improvements;
- Energy performance assessments carried out for other purposes;
- Data collected to demonstrate compliance with element 35 of SHQS; and
- Modelling based on similar properties in stock.
5.3 It is important for landlords to collect available data on the energy performance of their stock. This should include records of energy efficiency measures installed to allow the modelling of data for similar types of property. New EPC data and SAP calculations should be used on an ongoing basis to check and refine the quality of modelling. Whatever approach is taken, landlords will need to be assured that their information is fully robust, supports business and investment planning processes and enables accurate reporting to the Scottish Housing Regulator.
SAP and RdSAP
5.4 Reduced Data Standard Assessment Procedure ( RdSAP) uses the same calculation methodology and algorithms as SAP to calculate energy performance. For new buildings SAP calculates individual U-values for heat loss through the different fabric components of the building. In existing buildings, it would be very difficult to identify all the layers of an existing wall construction to allow a U-value to be calculated without intrusive surveys. U-values measure how effective a material is as an insulator. The lower the U-value, the better the material is as a heat insulator.
5.5 RdSAP was developed as a way of completing the SAP calculation for existing dwellings. Rather than entering the specific dimensions of all of the fabric components, default U-values were adopted taking account of the known insulation levels, construction type of the component, and the age of the building. The overall difference in the SAP score produced by full SAP 2012 and RdSAP 2012 programs is usually small, but there is a difference, especially for more complicated buildings.
5.6 For a more detailed discussion of the technical differences between SAP and RdSAP see the summary of technical assumptions in the research on developing an energy efficiency standard for private sector housing at http://www.gov.scot/Publications/2015/11/4536/7. For the purposes of EESSH it will usually be sufficient to note that an EPC for an existing building will normally be based on RdSAP. While a model exact evaluation might make a small difference to the overall rating, the use of RdSAP is sufficient for the purposes of evaluating the overall energy efficiency of social housing stock.
Using different versions of SAP
5.7 Different versions of SAP may produce different results. The overall rating band for energy performance is the same for all versions of SAP (see Table 6).
Table 6: SAP ratings and EPC bands
|SAP Rating||EPC Band||SAP Rating||EPC Band|
5.8 The SAP guidance includes conversion tables from previous versions of SAP.
A conversion table for SAP 2005 to SAP 2009 for different fuel types is at table 15 on page 205 of the BRE guidance at https://www.bre.co.uk/filelibrary/SAP/2009/SAP-2009_9-90.pdf, and a similar table for SAP 2009 to SAP 2012 is at table 15 on page 231 of the BRE guidance at https://www.bre.co.uk/filelibrary/SAP/2012/SAP-2012_9-92.pdf. These tables are given at ten point intervals but the scales are linear. However, the differences between ratings will also be affected by the differences in the range of data collected in different versions of SAP. The values for SAP 2012 given in Table 1 on page 4 above are based on recalculation of case studies used in the development of EESSH.
5.9 Landlords should make use of the best data available to them. Data from previous versions of SAP can be used to model compliance with EESSH. Landlords should, however, appreciate that later iterations of SAP are more accurate and should be given greater weight in their comparison of data. It is recognised that in specific circumstances (i.e. where identical characteristics apply across a number of houses), it would be appropriate for social landlords to advise SAP assessors of common technical data to assist in the production of accurate assessments.
Discrepancies in EPC data
5.10 Landlords in the Review Group identified examples of inconsistencies between SAP ratings carried out in different assessments. Landlords should be aware that it is possible for SAP calculations to include errors, and with accepted margins of error within the SAP rating, these can vary slightly between two EPCs of the same property carried out by different assessors. Where a landlord has strong archetype data of their stock and may wish to clone SAP ratings, they can choose EPCs that provide most comfort but they must have robust reasons to justify their choices. It is also recognised that modelling software will provide an estimated SAP rating which at times may vary slightly from an actual SAP rating once an EPC has been completed. In circumstances where the actual SAP rating is lower than the modelled SAP rating, and this results in the property not meeting the EESSH (despite all the energy improvements being carried out as per the modelling), the landlord may regard the property as EESSH compliant. The landlord must be prepared to prove they have a robust modelling methodology when making such decisions.
5.11 Landlords should also bear in mind that all versions of SAP are models and may not correspond to the actual energy performance of individual buildings. For example, SAP methodology assumes that buildings are in good condition and will not reflect problems such as disrepair and dampness which makes homes harder to heat. In some cases, landlords will have independent data on the energy use of a house from smart technology. The energy efficiency improvements driven by the EESSH are intended to make it easier for tenants to heat their homes comfortably. While the Scottish Government considers that a specific target is a useful measure of performance across the housing sector and the SAP is currently the best tool for measuring that performance, landlords will have to take account of the real life impact of change. Good quality data will be helpful if landlords find that it is necessary to evidence difficult decisions on appropriate measures in individual cases.
Anticipating new technology
5.12 New technology is not always well-reflected in SAP assessments. Appendix Q of the SAP methodology includes a process for evaluating innovative technology. For more information see http://www.ncm-pcdb.org.uk/sap/page.jsp?id=18 This process takes time and requires evidence from product testing. The EESSH provides a measure for progress in the improvement of social housing stock but it is not intended to act as a barrier to investment in innovative technology. The Review Group considered the example of infra-red heating systems, which have a relatively low running cost and are suitable for traditional buildings, but which are classed for the purposes of SAP methodology as storage heaters. This methodology gives a much lower modelled energy efficiency than is actually experienced by tenants. If landlords are satisfied that an innovation provides tangible benefits for energy efficiency and is in the best interests of tenants, they can consider a measure which, on paper, does not meet the minimum standard. Landlords must be satisfied that they have robust evidence to support this decision. This should include:
- Evidence that the technology provides an improvement in the thermal efficiency of a building;
- A reasonable expectation that future improvements in the evaluation of energy efficiency will recognise the benefits of the technology;
- Engagement with tenants to show support for the technology; and
- Ongoing monitoring to demonstrate benefits.
5.13 In all cases, landlords should seek to act in the best interests of tenants in the selection of appropriate energy efficiency measures. The EESSH should not dictate against appropriate and sensible investment, and innovative and creative approaches are encouraged.
SAP and traditional buildings
5.14 SAP methodology treats traditionally constructed buildings in the same way as other buildings. Pre-1919 construction is recognised as an area where homes are particularly hard to treat. Energy efficiency improvements should take account of appropriate materials and the need for ventilation to allow buildings to breathe. The SAP methodology does not allow for building specific construction data to be factored into assessments. This means, for example, that lists of proposed measures generated with an EPC may not be appropriate for these buildings. For further discussion of traditional buildings see paragraph 7.4.