How can the same property have such different EPC ratings?



Earlier in the year, Survey Hub were instructed to carry out an EPC (Energy Performance Certificate) at an industrial unit in Leicestershire. When the client instructed the job, they said there had been an EPC carried out recently but were not 100% sure if the rating was accurate, and wanted a second opinion. The current rating was a G 205.

Figure 1 Original Survey Carried out April 2018
Software used: Lifespan SBEM v5.4 using calculation engine SBEM v5.4.a.1
Accreditation Scheme: Stroma Certification Ltd
Date of survey: 23rd April 2018

Figure 2 Survey Carried out by Survey Hub July 2018
Software used – DesignBuilder SBEM v5.4.0 using calculation engine SBEM v5.4.b.0
Accreditation Scheme: Elmhurst Energy Systems
Date of survey: 6th July 2018

Stage 1 – Site survey

So that we can give an accurate second opinion, we must attend the site to carry out our own EPC survey. We measure the entire building, taking detailed notes and photos of the lighting, HVAC, hot water, construction materials and insulation etc. We also investigate the main fuel source servicing the HVAC systems, as this can have a huge effect on the rating.

Stage 2 – Office based research and processing

When we get back to the office we spend time researching the property online. First, we look at all planning applications made on the property – this helps us to identify the age of the building and if the building has been added to over time. Not all properties have their planning applications fully listed, but in this case we found information dating back to 1972.

Unfortunately, there had been no details listed with the dates and no documents available, therefore we must make some quantifiable assumptions. From photos taken on site, we can see the roof is made from composite roof panels, so we can confidently say that they’re insulated, but we have no other information. This would give us the worst-case U-value for an insulated roof. (We think this is the part of the survey that has been approached differently between the assessors. The warehouse roof had a large surface area and if the previous assessor had said that it was completely un-insulated, the heat loss here would cause a drastic effect on the rating).

Once all of our additional research is complete, we can then move onto drawing up the model. The software we use is a visual tool, so this makes it much easier to run through your final checking stages before reporting back to the client.


When assessors have to make assumptions, we must give the reasons for our decisions. In this case, the original assessor may not have made the same assumption with the roof as they couldn’t prove that it was insulated. Also, not only have we used different software but there was a software update between the surveys taking place, in this update the efficiency of LEDs had been increased and from our photos we know there were several LEDs in the property.

It’s hard to be certain as to why the ratings are so different as we don’t have the original site notes and research. If, however, surveyors don’t spend that extra time researching the building and all the HVAC, then they could end up basing their model data on inaccurate assumptions. Most assessors will default to the worst settings possible if they can’t prove their decision.

Share this post

If you’re interested in our services and expertise, please get in touch.