Why Has My EPC Rating Gone Down?

EPC rating going down

The top 5 reasons why your EPC ratings may have gone down.

There are many reasons why your epc rating has gone down. The top 5 reasons are:

  1. You’ve changed the heating system to a more expensive source of heating, for example from storage heaters to panel electric heaters that use peak rate electricity.
  2. Lack of documentary evidence provided to the EPC Assessor
  3. Data entry error by the Assessor on the old EPC Certificate
  4. Data entry error by the Assessor on the new EPC Certificate
  5. You have a new build property that has had a new EPC

Now let’s look at each of the above in more detail.

1. You’ve changed the heating system to a more expensive source of heating

Two types of heating systems rate very poorly on the EPC they are peak rate electric, and LPG (liquid propane gas).

If you have changed the fuel source used for heating to one of these, then expect to see a substantial drop in the rating. This is because these sources of fuel are the 2 most expensive ways to heat a home and the EPC rating is based on the running cost to provide heating and hot water to the property.

If the property also has poor insulation and an expensive fuel source, then it’s unlikely that the property will even reach E rating required under the Minimum Energy Efficiency Standard.

The most common of all the fuel source changes we see is changing storage heaters on an off peak tariff, to panel electric heaters that use electric at peak rate.

This topic has it’s own article that can be read on the biggest mistakes landlords make, that actually lowers the EPC rating.


Change to a cheaper source of energy if possible, and/or upgrade the insulation to poorly insulated areas of the home.

The Nottingham Energy Partnership has an excellent domestic fuel price comparison on their website. There you can directly compare all fuel types in pence per kwh.

2. Lack of documentary evidence provided to the EPC Assessor

Lack of documentary evidence is one of the major reasons why your EPC rating may be lower. Whereas your previous EPC Assessor may have had evidence to support a particular data entry, your new EPC cannot simply copy that information, the current Assessor will also need to take copies of documentary evidence.

Documentary evidence needs to be provided where an Assessor cannot see an improvement that has been carried out. This typically applies to upgrades in the following areas of the home:

Internal or external wall insulation
• Sloping roof insulation
• Flat roof insulation
• Underfloor insulation
• Date loft conversion was carried out

Restricted Access to key areas needed for the EPC

In most cases the Assessor will come across most items they need to see whilst going around the property. However sometimes it may be difficult to gain access to these items which will lead to a lower rated EPC.

Loft Access
• Boiler Access
• Hot water cylinder access
• Boarded lofts where the insulation depth can’t be determined.


Provide documentary evidence of the insulation improvement that has been done, such as a receipt or invoice or architects plans from the contractor stating what was done and the thickness of the insulation added.

The evidence must also show the property address.

For loft rooms conversions, the building control completion certificate is excellent evidence.

In the case of restricted access, make sure that the items mentioned above are accessible.



3. Data entry error by the Assessor on the old EPC Certificate

We’re all human and data entry error by the Assessor can be made.

However, don’t always assume that because the old EPC showed a better rating than the new one, that it was correct in the first place.

EPCs were introduced as a legal requirement for a property being sold or rented in May 2010. As this was a new scheme at the time, some of the early EPCs were of poor standard, so much so that all Assessors were de-registered in 2012 and had to re-train.

EPCs carried out now are of a better standard that use standardised conventions across the board for all Assessors. In addition, Assessors are continually audited by their accreditation body to ensure high standards are maintained that follow clearly defined conventions.

This also means that a new EPC is often an auto correction on an older EPC done over 10 years ago that may have been incorrect.


Ask your Assessor to provide information as to what has caused the variation in the EPC rating.

4. Data entry error by the Assessor on the New EPC Certificate

Again, a data entry error could have been made by the new Assessor. However, it is more likely that the error was made on the old certificate.

A recent example we had of this was a customer who raised the query as to why their previous EPC was rated a D 62 whereas the one we had just completed rated the property an E 54 for their mid terrace home.

Our investigation highlighted a glaring error on the old EPC which measured the floor area of the building at only 33m2 when in fact it was 76m2.

This had the impact of the old EPC having a lower running cost per m2 and hence an incorrectly higher rated EPC.


Ask your new Assessor to check the reason as to why the newer EPC may be lower.

If the Assessor find any errors they have made, the EPC should be corrected free of charge.

The Assessors contact details can be found on the last page of the EPC.

5. You have a new build property that has had a new EPC


New build properties are built to a very high standard. When the first EPC for a new build is done it is done from the building plans using a methodology called SAP.

SAP stands for Standard Assessment Proceedure and is the UK governments methodology for calculating energy efficiency in buildings.

An EPC produced using SAP will produce a very accurate energy rating of the property because the exact thermal values of all the construction elements, i.e walls, roof, floors, windows would be known.

Also, all new build properties have to pass the demanding low CO2 emissions as part of the building regulations. To achieve these carbon emmision targets often mean that the thermal values are usually over and above the minimum values actually required by the building regulations.

When the SAP EPC has expired and a new one has to be produced, it uses a different methodology called RDSAP.

RDSAP stands for Reduced Data Standard Assessment Procedure. This is used on all existing dwellings because a full set of data thermal values is usually not available. RDSAP uses default thermal values for the walls, roof, floors, and windows, based on the minimum building regulations for the age of the property.

Therefore if the builder has built a property with higher thermal values than those required by the building regulations, this wont be reflected in RDSAP and will result in a lower EPC rating.

Air Tightness Testing

The second reason why a new build may have a lower EPC rating that previously, is that at the end of the property construction it would have an air tightness test and the exact figure from that test would be entered into the SAP software.

Most new build properties would achieve an air tightness result of between 4m3/hm2 @ 50 Pa and 7m3/hm2. The lower this value the better.

It wouldn’t be practical for an existing building to have an air tightness test. Therefore the RDSAP software uses a default value of 15m3/hm2 @ 50 pa, which is significantly worse than what the property may have achieved when built.

The combination in the variation in the thermal values between SAP and RDSAP and the lack of an air tightness test in existing dwelling will generally result in a lower EPC rating of 2 to 3 points.


There is no real solution to this one, because the homeowner would typically have no full architectural drawings of their home.


  1. Hayley Farnfield

    I had original EPCs done in 2013 on flats and they came out as Flat 1 – B and Flat 2 was a C rating.
    In Nov 2023 I had new EPCs done and they came out a band lower.I queried this as on report it said I had single glazing and no mention of insulation but I have special heritage approved double glazing . I sent off a email with evidence proving I had special double glazing and insulation as part of the planning documents and building sign off. I asked the assessor to include this in the hope the grading would be improved .
    Now the assessor is saying they have gone down again to an E for Flat 1 and a D for flat 2.
    How can that be ?
    How can the same flat go from a B to a D to an E . Assessor is asking for more money and the company is saying new software installed might have affected the rating !!
    Does all this sound normal ?

    • Rickie Dickson

      Hi Hayley
      If you provide me with the addresses of the flats, I’ll have a look at them to give you a better idea what may be going wrong. Drop me an email to [email protected].
      Rickie Dickson


Submit a Comment

Your email address will not be published. Required fields are marked *

Rickie Dickson

Written by Rickie Dickson

Rickie Dickson is an experienced and qualified domestic and non domestic energy assessor. He helps homeowners and businesses in all matters relating to energy efficiency, from meeting building regulations compliance to improving a property’s energy rating score.