This guidance will explain the differences between the methodologies and help you decide which is appropriate for an energy assessment on a domestic property.
SAP
The SAP methodology is used to assess newly built and newly converted dwellings in order to demonstrate that they comply with the requirements of Building Regulations. In Scotland, a dwelling created by conversion does not require a SAP calculation (such works are exempt from standard 6.1 (carbon dioxide emissions) and standard 6.9 (energy performance certificates).
A SAP assessment is produced at both Design Stage before the works take place and at As Built Stage when the works have been completed, at both points of the development the compliance is assessed. When the dwelling is complete, it will be a requirement to lodge a SAP EPC in addition to providing a Building Regulation Compliance Report which shows Building Control that the standards have been met and the dwelling can be formally signed-off. In Scotland the submission of SAP calculation is only sought at design stage. On completion of the dwelling, a SAP EPC must be produced and submitted alongside the completion certificate for each dwelling.
In addition for compliance purposes (optional in Scotland), a SAP assessment may also be required when an existing dwelling is being extended and the amount of glazing present in the extension exceeds 25% of the floor area, in these scenarios Building Control will need to be shown that the addition of the extra glazing is not detrimental to the energy performance of the dwelling.
RdSAP
This is the government approved methodology for energy assessments of existing dwellings. An existing dwelling is one which was completed prior to the below dates or has been completed and signed off by building control or for Scotland a completion certificate has been submitted and accepted by the local authority verifier.
England & Wales – 6th April 2008
Northern Ireland – 30th April 2008
Scotland – 7th January 2013
Completing an RdSAP assessment requires the Domestic Energy Assessor (DEA) to fully inspect the property taking evidence of assets such as the heating system, insulation, ventilation.
Appendix S of the full SAP methodology defines what data should be collected and what assumptions are applied.
An RdSAP assessment must be completed for domestic dwellings that are being marketing for sale or rental with an EPC being lodged. Estate agents and Letting agents are responsible for displaying the energy rating of a property. An RdSAP assessment and/or an EPC may also be required for government funding polices such as the Energy Companies Obligation (ECO).
RdSAP and Newly Completed Domestic Dwellings
Where a dwelling is newly completed an RdSAP EPC cannot be used for compliance sign off. However, an RdSAP EPC can be lodged as long as the compliance stages described above have been completed.
There will be situations where it is unclear if the dwelling has been signed off. Where this occurs the DEA should inform the home owner that they are entitled to a full SAP EPC and direct them to the party responsible for the build (e.g. the builder) should they wish to follow this up. The DEA can continue with an RdSAP assessment and lodge an EPC where they have informed the home owner fully of the process detailed in the above sections and this is documented with the DEA’s evidence.
Conclusion
RdSAP is for existing dwellings. New dwellings (including conversions from non-domestic or domestic except in Scotland) should have a full SAP assessment when completed and before occupied; however, this is the responsibility of the builder, not the DEA. Having an RdSAP EPC assessment does not preclude a SAP EPC assessment being done later to meet legislative requirements.
Where a property was originally a dwelling but is presently used for other residential purposes and could be reasonably used as a dwelling with no alterations to the building, then an RdSAP EPC can be lodged. Examples would include houses now used as B&Bs or HMOs. Examples that require non-domestic EPCs would be a purpose built hostel or residential home.