Energy Reporter - How is the Energy Performance Certificate measured?

The Energy Performance Certificate is measured using a system called the Reduced
Data Standard Assessment Procedure (RDSAP). This system was developed from the
Standard Assessment Procedure (SAP). In order to provide a like for like comparison
between different properties regardless of its inhabitants, both the RDSAP and the SAP
make certain assumptions about the way the occupants use the property. This is called
‘standard occupancy’ and it ensures that the properties rating is not biased by the
occupiers demand for energy. ‘Standard occupancy’ assumes that the house will be
heated for 9 hours a day in the week and 16 hours a day at weekends, with the living
area heated to 21°C and the rest of the house to 18°C. The difference between RDSAP
and SAP is that the former requires much less data input than the latter and can
therefore be done relatively quickly and cost effectively. The full SAP is often calculated
before a building is constructed and ensures compliance with current building regulations
relating to energy efficiency. It requires knowledge of building materials that may not be
able to be seen after the house has been constructed. RDSAP was developed to enable
surveyors to gauge the energy efficiency of existing properties. Like a valuation or even a
structural survey, the RDSAP survey is a non-intrusive survey. This means that the
surveyor is not allowed to disturb the fabric of the building and must not cause any
damage. Any furniture and belongings should not be moved without permission. This
clearly limits the information that is obtainable, however recent surveys of houses that
have had both the SAP and the RDSAP calculations seem to suggest that the RDSAP
system produces very similar results to the full SAP system. If the inspection of certain
areas of the building is restricted, the DEA is required to note them on their site notes
and input the restrictions into their RDSAP software as ‘no access’. The software will then
assume that the property meets the minimum building regulation standards of the time of
construction and generate an EPC accordingly. It is always wise to allow the DEA as
much access as possible as the software will default to the lowest levels of efficiency
possible within building regulations for the date of construction of the property if an area
cannot be inspected. For example if the roof insulation cannot be inspected the system
will often assume (depending on the houses age) that there is none present. If the roof is
insulated but the DEA could not verify this it will be recorded as ‘no access’ and your EPC
will be significantly affected.

What are the key elements of the property that RDSAP measures?
Key pieces of information that are collected include the property age, dimensions,
number of extensions (an extension can be part of the original construction, it is defined
as ‘thermally different’), wall type and insulation, roof type and insulation, window type,
presence of a room in the roof, presence of a conservatory, presence of low energy
lighting, primary and secondary heating systems and their controls. If you would like to
learn more about how to prepare for an energy performance inspection click here
Elements that aren’t measured in the Energy Performance Certificate include floor
insulation, electrical appliances in the property, unnecessary portable electric heaters,
the location of the property (north / south, mountain top / sea side) or how you use your
property.

If you would like to know more about how to prepared for Energy Performance Certificate
inspection click here