Energy Performance Certificate based on SAP

I have now had a full SAP assessment for the refurbished house.  The Environmental Impact Rating is band A.

The Standard Assessment Procedure (SAP) is the methodology used by the Government to assess and compare the energy and environmental performance of dwellings. Its purpose is to provide accurate and reliable assessments of dwelling energy performances that are needed to underpin energy and environmental policy initiatives.  EPCs for the purposes of selling or renting a house are carried out on a less detailed assessment.

As I discovered before, the basic EPC assessment can’t cope with non-standard features, such as a heat recovery system or good airtightness, so underplayed the performance of the house.  SAP does take such things into account because it is much more detailed, and the SAP can then be used to provide the EPC.

Our Energy Efficiency Rating (EER) came out at almost 91, so just below the A band, which starts at 92.  Disappointing to be so close to and yet not quite an A, but a vast improvement on the C rating that resulted from the basic EPC assessment.  ‘A’ ratings typically require a full calculation of all the heat losses through thermal bridges; this is very difficult if not impossible for a retrofit.  We definitely have some residual thermal bridges, so it is fair enough that we fall short of the very best rating.

Just as I was feeling better about having almost reached  ‘A’, the SAP software was updated to take into account increased energy prices.  Electricity prices were increased from 11.46 p/kWh to 13.19 p/kWh.  Our rating decreased from 91 to 84 – though this is still in the ‘B’ band.  What I then learnt is that the main ‘Energy Efficiency Rating’ displayed prominently by estate agents is based on fuel costs, rather than energy used (contrary to what you might think from its name). Electricity is more expensive than gas, so our all electric house doesn’t come off as well, even though it is actually using comparatively little energy.

Then I discovered that, tucked away at the end of an EPC, there is another rating: an Environmental Impact Rating (EIR), which is a measure of a home’s impact on the environment in terms of its carbon dioxide emissions.  Here, our score is 95, or A rated.  Hurray!  This is more like it.  When we only had a summary EPC calculation before, the EIR was only 77, or C band, reflecting the fact that the less-detailed assessment didn’t look at, for example, the heat recovery system or airtightness.

So two lessons learnt:

  1. A full SAP assessment is required  to take into account the special low energy technologies, such as heat recovery with the ventilation system, and airtightness.
  2. The Environmental Impact Rating tells you about carbon dioxide emissions, whilst the Energy Efficiency Rating focuses on cost.

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