Case Study 5 - 1950s Semi - Scrutinising an existing EPC

This 'case study' is based on an auction property that came up for sale just around the corner from where I live.

I saw the property listed on RightMove and visited the property on a viewing day.

I’ll present some information about the property and I wonder whether I can lead you into making any observations about the EPC, what the EPC has assessed, and maybe what it hasn’t, and if there are any clear ways the EPC rating could be improved (there’s at least a couple).

So this is a 3-bed semi-detached house, a former local authority property, built in the 1950s.

In passing, not that this has any relevance to EPC assessments, but notice the adjoining house next door has the original concrete Finlock guttering. On the house we are looking at however, the concrete guttering blocks have been completely removed, the rafters extended and a soffit/fascia box created, extending out from the property slightly, and shallowing the angle of the lower two rows of tiles on the roof.

The preferred way to remove this type of guttering nowadays is to just cut the concrete gutter trough off, leaving the remainder of the Finlock blocks in place and facing them with an insulating material then uPVC facia and guttering.

I notice this because my house also has the original finlock guttering and at some point in the future I'll need to get it removed.

Back to the EPC however, an assessment was conducted in Q2 2025, just a short while before the property was marketed for sale, and conducted against the RDSAP v9.94 methodology in use at the time.

I mention this because RDSAP 10 replaces RDSAP 9.94 on the 15th June 2025 and the Home Energy Model is reported to replace RDSAP completely in 2026. EPCs conducted up until these points in time will have been conducted under the methodology in use at the time, and should continue to be valid until the end of their 10 year life.

Here’s the floorplan and a further picture of the property:

Here’s some information from the first part of the EPC:

Do you notice anything about the floor area?

Ready?

The floor area indicated on the estate agent’s floorplan is 20% greater than the floor area indicated on the EPC.

Why might that be? 

Ready?

Well, looking at EPCs for other properties on the same road, 82m2 seems to be the typical floor area for neighbouring properties, so I think the EPC only covers the main building, and not the ground floor extension at the rear, or the ‘storeroom’.

Should the ground floor extension on the rear be included in the EPC assessment? ..and if so how would that affect the EPC rating?

Firstly, do we consider the extension to be a conservatory?

Well for EPC assessments, a conservatory is defined as having more than 50% glazing to the walls and more than 75% glazing to the roof.

In this case, from the photo above, the very limited amount of glazing to the roof of this ground floor structure means this is not classed as a conservatory, and would be classed as an extension instead.

So, should this extension be assessed as part of the EPC?

My understanding is that under the current methodology (RDSAP 9.94):

• A conservatory would be excluded from the assessment if it was thermally separated from the main building, regardless of whether it had a fixed heating emitter driven by the main heating system of the house, or not.
• An extension though would be included in the assessment if it contains a fixed heating emitter driven by the main heating system of the house, regardless of whether it was 'thermally separated' or not.

'Thermally separated' means that the conservatory/extension has an external quality door separating it from the main building. If there was no separating door, or an 'internal' quality door was present then the conservatory/extension is not 'thermally separated'.

So, with this being an extension rather than a conservatory, it raises the questions: Does this extension contain any heating emitters linked to the main heating system of the house?... and do external quality doors separate it from the main building?

From the photo above, there is clearly a 'wet' radiator in the extension, connected to the central heating system of the main building. A photo from a different view of this was also present in the Rightmove listing.

Also, the doors shown here on the rear of the main building (from the lounge/dining room to the extension) are external quality ones. The door from the kitchen to the extension is also an external quality one (not shown here).

Due simply to the presence of the fixed heating in the extension, I therefore believe the extension should have been included in the EPC assessment, but was not. If you think I've got that wrong please let me know.

Had that extension been included in the EPC assessment, I believe the EPC rating would have been reduced. I doubt that any evidence is available to prove a construction date of the extension and I have not been able to find any applications on the Wiltshire Council planning portal.

From various small observations about the extension, I also doubt that it was built to comply with Building Regs at the time, not that that is a consideration necessarily for EPC assessments, other than sourcing information regarding construction dates.

The question of whether the extension should be included in the EPC or not is fairly important, because if it is included, then the EPC rating would probably be degraded due to the large expanse of glass (with unknown install date) and the sloping ceiling where we cannot be sure of any insulation status.

Because access is not available to check whether insulation is present in that sloping ceiling and no evidence is available to prove the construction dateband, we would have to set the construction dateband of the extension to be the same as that of the main building.

In this case, it would be: 1950-1966 (England & Wales). This would result in the methodology assuming there was no insulation present in that roof and using a very poor U value to use when calculating the resulting EPC rating.

How could you remedy this?

• Remove the radiator so that the extension does not need to be included in the EPC assessment (best option)... or
• Conduct invasive inspection to identify what insulation is present and get someone qualified to provide documentary evidence for the next EPC assessment.
• Potentially following the last point, get a custom U-value calculation conducted based on the information obtained, but this is probably not worthwhile.

Next, here is the Features table on the EPC:

Is there anything that stands out on the Features table?

Ready?

There are two things that interest me,

The first is the description of the roof. There is only one description of Roof which further supports the belief that the EPC does not include the extension. If it did, we’d expect to see a second entry for Roof referring to flat/sloping roof. 

Notice that the roof is described as:

Pitched, no insulation (assumed)

That’s a fairly rare description. You’d normally expect to see something like

Pitched, 250mm loft insulation

..or something very similar.

So why does it say: no insulation (assumed)?

Take a few moments and make a list of reasons you think this entry might be present.

Ready?

The ‘assumed’ in brackets means that the assessor was not able to access where insulation might be in order to record its presence.

This could be because:

• The loft hatch is locked/sealed shut
• The loft hatch is unsafe to use
• The loft is unsafe to access
• The loft has been boarded out, covering the insulation
• The loft is full of items to the extent that the insulation is not accessible to measure.
• There is no loft hatch

The EPC methodology (currently RDSAP v9.94), not the assessor, then reverts to the construction dateband of the building and makes an assumption of how much insulation is present based on the most common level of insulation used at that time.

For the construction dateband of this building, likely 1950s and therefore with a dateband of 1950-1966 (England & Wales), the assumption is there isn’t any insulation, because it wasn’t required at the time, and modern building regulations were only introduced in 1966.

Upon viewing the property I found that a loft hatch was present, it was usable, and I took the following photos in the loft area.

So we can see that there is a limited amount of insulation present – just up to joist deep which was 100mm, but over a fair proportion of the area the joists are covered with boards, hiding the insulation beneath them.

The assessor, despite being a direct employee of the organisation that owned the property, exercised his right to declare the insulation status as ‘Unable to determine’ because of the boards.

There are various reasons why this is an entirely reasonable decision, particularly relating to insurance cover and the fact that for health & safety reasons Domestic Energy Assessors are only expected to conduct a head and shoulders inspection through the loft hatch.

The choice of optons for the roof type as 'Pitched Roof, Access' with an insulation status of 'unable to determine', for this constrution dateband, results in the roof description in the EPC Features table reading: “no insulation (assumed)”. This will have certainly resulted in a drop in EPC rating. 

For my property, of a similar age band, but a mid-terrace rather than a semi, the same situation would have made a difference of 5 SAP points to my EPC rating. We cannot necessarilty make a direct comparison however.

How could you resolve this situation?

You could:

• Simply remove the boards from the loft.. or
• Find another assessor who is prepared to lift the boards momentarily themselves... or
• Get the property re-assessed while you lift the boards momentarily yourself so that the level of insulation can be confirmed by the assessor as uniform across the whole of the loft area.

One thing to mention is that when the insulation status of a pitched roof is set to 'Unable to determine', this also supresses any recommendation to increase the loft insulation thickness on any resulting EPC.

If you bought a property that already had an EPC with a similar roof description but where access is easily available and insulation is clearly present, do be aware that the EPC was conducted prior to you owning the property and there may have been an obstrution of some sort preventing access at the time of inspection, which you currently would not be aware of.

The next item I noticed on the EPC Features Table is on the last line, where it says:

Secondary Heating: Room Heaters, Electric

This is not assumed (the word assumed is not present in brackets after it). Had it been 'assumed' then this would have been due to the observed heating provision in the property not being sufficient to heat the house. The methodology would have added that entry automatically to balance the heat demand. This would happen for instance if you have a habitable room that is not heated, and there are no other forms of secondary heating present.

In this case though, it is not 'assumed'. This means the assessor actually identified a fixed electric room heater somewhere in the property (portable heaters don't count).

In the csae of this propery, it's main heating system is driven by a gas boiler. That's really good (for domestic EPCs currently), and you would expect this to lead to a good EPC ratingg.

However, this is affected when a source of secondary heating is identified. This could be any additional fixed source of heating within the property, such as an open fireplace with a grate, a gas fire in the living room, a fixed electric panel heater etc. The methodology assumes that a proportion of the floor area of the property is heated by that secondary heating source, even if you don’t actually use that heating source in your day to day occupancy of the property. A secondary heating source may use it’s own, different fuel type, and when this differs to the fuel type of the main heating system the EPC rating can be affected.

Electric secondary heating is about the worst form for two reasons:
RDSAP assumes 20% of the area of the property will be heated by the electric secondary heating source, whereas for most other fuel types it assumes 10%.

Electricity is also a much more expensive fuel compared to gas (per kWh), and one of the most expensive of the main fuel types.

Overall, with our example here where we have a cheap to run gas boiler heating 80% of the house, 20% will be assumed to be heated by the more expensive peak rate electric heating.

The methodology will calculate it costs more to heat this property than if it only had a gas boiler. The EPC rating will therefore be worse.

(a quick note here just to advise that this behaviour does not occur when the main heating is provided by electric night storage heaters. The addition of electric secondary heating does not appear to affect the EPC rating).

In the example of my property, which uses a condensing gas combi boiler, the presence of electric secondary heating would reduce my EPC rating by 6 points.

So, is there anyting we can do to resolve this degradation of the EPC rating of this building?

This raises the question: Is a form of secondary heating really present in the property?

In the photographs on Rightmove we can see an electric feature fireplace in the lounge. During my visit to the property I took this photo and identified that this was the only form of secondary heating present in the property:

This has the appearance of an electric feature fireplace, and was placed against the chimney breast there.

Does this electric heater qualify as a form of secondary heating?

In my opinion, it should not.

This is because it is not fixed in position in the fireplace, and the cable has a plug on the end of it, rather than being hard-wired into a switched fused spur on the wall. It could easily be removed from the property in a matter of seconds, and should be classed as a portable heater which does not come under the scope of an EPC assessment.

So in my opinion, this is the second mistake in the EPC assessment for this property, and a third opportunity.

The next question is: How can this issue be resolved so that this no longer affects the EPC rating?

In this case, to avoid any possible doubt, I would simply remove the electric heater, and check that all habitable rooms are heated by the main gas boiler in some way, normally by radiators or underfloor heating. In this property they are.

In this specific case, this was the only form of electric heating present, so you could potentially contact the assessor of the EPC and put forward this observation and you could probably expect them to re-issue the EPC correctly.

Otherwise you could just remove the heater so there is no doubt, and get the property re-assessed by another assessor once you’ve carried out any other works you might have planned.

I hope this has been interesting.