We are in the process of buying a BISF house which has a current EPC rating in the mid-30s and a maximum EPC rating in the mid-60s.

What confuses me is that other houses of exactly the same construction that are on sale in the area have completely different maximum EPC ratings. Some have maximum EPC ratings of over 80, while others have maximum ratings in the 50s.

What’s the reason for this disparity? How can two houses of the same construction have such widely different maximum potential for energy efficiency?

What’s a realistic maximum rating for a BISF house?

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Thanks for this update.

I understand what you’re saying. When a house has an energy improvement installed (e.g. a better boiler, loft insulation), the EPC rating improves. That totally makes sense to me.

What doesn’t make sense is the maximum (i.e. top potential) rating. How can houses constructed in the same way have wildly different potential ratings? Surely their potential is all the same?

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Hello Ant2150

I can fully understand your confusion with Energy Performance Ratings or EPC’s.

You would expect that if there were three identically constructed houses sitting side by side, that they would have identical EPC ratings but it is not quite as straightforward as that.

You see, property 1 may have loft insulation and gas fired central heating with each of these additions or measures carry a set number of SAP points.
Property two may have no loft insulation, no central heating, no energy saving light builds, so this property would have a lower SAP rating because SAP points are awarded depending on what measures you have in place. The higher the rating the better performing the property is.
Property 3 could have every possible energy performance enhancing system in place including wall insulation, triple glazed windows, draught proofing etc. Each one of this carry a high SAP rating meaning the property is more efficient and probably in bad A.

So in reality it’s not about just the house, it’s about what systems are in place to help the house perform well, reducing energy consumption which in turn reduces carbon emissions.

I hope this helps.

I have listed a little more information below.

Energy performance certificate EPC ratings explained

EPC ratings explained Energy Performance Certificates bands

A typical inspection takes around one to two hours to carry out, depending on the size and layout of the property. After the property has been inspected, the energy inspector will use software to calculate the energy rating for the property. An energy performance certificate will then be produced which will tell you all about the Energy Efficiency and the Environmental impact of your property. The certificate will tell you:

Energy Efficiency rating
Environmental Impact CO2 rating
Estimated energy use, carbon dioxide (CO2) emissions and fuel costs of this home
Summary of your home’s energy performance related features
Recommended measures to improve your home’s energy performance

The energy performance certificate comprises of two main charts: Energy Performance Certificate ratings & Energy Efficiency Rating.

The energy efficiency rating is a measure of the overall efficiency of a home. The higher the rating the more energy efficient the home is and the lower the fuel bills will be.

Impact CO2 Rating

The environmental impact rating is a measure of a home’s impact on the environment in terms of carbon dioxide (CO2) emissions. The higher the rating the less impact it has on the environment.

An Energy Performance Certificate (EPC) shows the energy current and potential energy rating of a property, known as a ‘SAP rating’. A ‘SAP’ rating stands for Standard Assessment Procedure and is the governments recommended system for producing a home energy rating. The SAP charts have been divided into 7 bands ranging from A-G. Each range has a set amount of ‘SAP’ points.

Each chart has a current and a potential energy rating out of a maximum of 100 points (being maximum efficiency).

As follows:

Band Rating Points
A 92-100 SAP points (Most efficient)
B 81-91 SAP points
C 69-80 SAP points
D 55-68 SAP points
E 39-54 SAP points
F 21-38 SAP points
G 1-20 SAP points (Least efficient)

*Please note that these are only estimates and may be inaccurate. What makes a different to the SAP rating? Below are some examples of aspects that can make a different to your property’s SAP rating.

Improvement Rating can be improved by Estimated Savings
Condensing Boiler – *47 SAP points – £225+ per year
Cavity Insulation *13 SAP points – £100-£125 per year
Roof Insulation *10 SAP points – £100-£125 per year
Double Glazing *4 SAP points £10-£15 per year
Low Energy Lighting *2 SAP points £10-£15 per year

Estimated energy use, carbon dioxide (CO2) emissions and fuel costs of this home

This tells you your current and potential energy use and carbon dioxide emissions per year. It also shows your estimated current spending on elements such as lighting, heating and hot water and what they potentially could be if you made the recommended improvements.

Summary of your home’s energy performance related features

The summary will assess the key individual elements that have an impact on your home’s performance rating. Each element is assessed against the following scale: Very Poor/Poor/Average/Good/Very Good.

The key elements that are considered are walls, roof, floor, windows, main heating, main heating controls, secondary heating, hot water, lighting.
Recommended measures to improve your home’s energy performance

The report will contain a section showing what the recommended measures that can be taken to improve the property’s energy efficiency.
We do not recommend that you carry out any of these recommendations yourself. We would strongly advise you to seek a professional in within the area of expertise required to discuss how the improvements could be made.

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