Factors affecting your EPC result

An EPC can feel surprisingly unpredictable.

You might have installed a new boiler, fitted double glazing and filled the loft with insulation, only to find your EPC has barely moved. Or you may be comparing your home with a seemingly similar property down the road and wondering why their rating is higher.

The reason is that an Energy Performance Certificate is not simply a checklist of improvements. Your EPC result is calculated from a combination of your property's construction, insulation, heating, hot water, glazing and other energy-related characteristics.

For existing homes, assessors generally use the government's Reduced Data Standard Assessment Procedure, or RdSAP. Because an assessor cannot open walls or floors to see exactly what is inside them, the methodology sometimes has to make assumptions based on the property's age and construction.

Understanding what actually affects your EPC can therefore be particularly useful when preparing a home for sale.

How is an EPC rating calculated?

A domestic EPC gives your property an energy efficiency score and places it into one of seven bands:

• A: 92+
• B: 81 to 91
• C: 69 to 80
• D: 55 to 68
• E: 39 to 54
• F: 21 to 38
• G: 1 to 20

A is the most energy efficient and G the least.

The score is calculated using information about the property rather than simply looking at your actual energy bills.

That distinction is important.

A person living alone who rarely turns the heating on could have very low energy bills but still own a poorly performing home. Equally, a family that keeps an efficient house at 23°C all winter could have relatively high bills.

The EPC attempts to compare homes on a standardised basis.

1. The age of your property

The age of your house can have a surprisingly large effect on its EPC result.

Building standards have changed enormously over time. As a result, the EPC methodology can use the property's approximate construction date to infer characteristics where they cannot be directly confirmed.

An older house might therefore be assumed to have:

• solid rather than cavity walls
• less floor insulation
• lower levels of roof insulation
• poorer thermal performance
• different construction materials

This does not automatically mean old houses receive bad EPC ratings. An extensively upgraded period property can perform very well.

But evidence of those upgrades can become important.

2. Wall construction and insulation

Walls represent a large external surface of most homes, so the amount of heat escaping through them can significantly affect the property's calculated energy performance.

Your EPC assessment may consider whether you have:

• cavity walls
• cavity wall insulation
• solid walls
• internal wall insulation
• external wall insulation
• modern insulated construction

A Victorian solid-wall house can therefore behave very differently in an EPC calculation from a modern cavity-wall property.

If insulation has been added, keep documentation showing what was installed.

3. Loft and roof insulation

Heat rises, making the roof another important part of a property's energy efficiency.

The assessor will look at factors including the type of roof and insulation present.

In a conventional loft, insulation may be relatively easy to inspect and measure.

Things can become more complicated where:

• a loft has been converted
• ceilings follow the roof line
• insulation is hidden
• an extension has a different roof construction
• insulation was installed as part of previous building work

If the insulation cannot be seen, documentary evidence may help establish what was installed rather than relying on an assumption.

4. Floor insulation

Floors can also contribute to heat loss.

The EPC calculation considers the type and thermal performance of the floor, although insulation beneath an existing floor is obviously much harder for an assessor to inspect than insulation sitting in a loft.

This is another area where the age and construction of the property can influence the assumptions used.

5. Your windows

The assessor will record the type of glazing installed throughout your home.

This can include:

• single glazing
• double glazing
• secondary glazing
• high-performance glazing

The proportion of the property that is glazed can also matter.

Replacing old single-glazed windows will normally improve the thermal performance of a property, although the EPC improvement may not always be as dramatic as homeowners expect.

This is because windows are only one part of the overall calculation.

6. Your boiler and heating system

Heating is one of the most important parts of an EPC assessment.

The type of heating system, its efficiency and the fuel it uses can all affect the result.

The assessment may consider:

• the type of boiler
• boiler efficiency
• gas, electricity, oil or other fuels
• heat pumps
• storage heaters
• direct electric heating
• communal heating
• secondary heating systems

An old inefficient boiler can therefore pull a property's score down.

But simply buying the most expensive replacement boiler does not guarantee a huge jump in EPC rating. The improvement depends on what it is replacing and the rest of the property's characteristics.

7. Heating controls

Your heating controls matter too.

For example, the assessment can take account of features such as:

• programmers
• room thermostats
• thermostatic radiator valves
• heating zones
• suitable heat pump controls

A modern boiler with poor controls may therefore not perform as well in the calculation as the same system with effective controls.

These can sometimes be relatively inexpensive improvements compared with major building work.

8. Hot water

The way your property produces and stores hot water forms another part of the calculation.

This can include:

• hot water from a combi boiler
• cylinders
• cylinder insulation
• immersion heaters
• heat pumps
• solar water heating

Even the insulation around a hot-water cylinder can contribute to the overall assessment.

9. Solar panels and renewable energy

Generating energy at the property can improve its energy performance.

Solar photovoltaic panels are the obvious example.

Depending on the system and methodology being used, an EPC assessment can take account of renewable technologies such as:

• solar PV
• solar water heating
• heat pumps
• other recognised low-carbon technologies

The size and characteristics of a solar installation can matter, so keep the paperwork associated with the system.

10. Lighting

The proportion of fixed lighting using energy-efficient bulbs can also form part of an EPC assessment.

Changing bulbs alone is unlikely to transform a poorly performing house into an A-rated one.

However, EPC scores are made up of lots of individual factors, and smaller improvements can become particularly important if your property sits close to the boundary between two EPC bands.

A property scoring 68 is a D.

At 69, it becomes a C.

That single point can therefore make the result look considerably different to a potential buyer.

11. Property type

Two houses with identical boilers and insulation can still receive different EPC results because the buildings themselves lose heat differently.

Consider the difference between:

A mid-terrace house

It shares walls with neighbouring heated properties on both sides.

A detached house

It may have four external walls exposed to the outside.

The detached home generally has a greater external surface area through which heat can escape.

Property characteristics such as whether the home is detached, semi-detached, terraced or a flat can therefore influence its energy performance.

12. The size and layout of your home

The assessor records measurements and characteristics of the building.

Extensions can also matter because different parts of the house may have been constructed at different times and to different standards.

A home might contain:

• an original 1930s structure
• a 1990s rear extension
• a 2015 loft conversion

Those parts of the property may have very different thermal characteristics.

13. Evidence of improvements

This is one of the most overlooked factors affecting an EPC result.

Your assessor cannot necessarily accept everything you tell them about the property.

If insulation is hidden behind plasterboard, for example, simply saying:

“There is definitely insulation in there.”

may not be sufficient.

For existing properties, RdSAP deliberately uses assumptions where some information cannot practically be gathered during a normal inspection.

That means paperwork can be valuable.

Before your EPC assessment, look for evidence relating to:

• extensions
• loft conversions
• wall insulation
• roof insulation
• replacement windows
• boilers
• heating systems
• solar panels
• building regulation approvals
• completion certificates

An energy improvement that cannot be adequately evidenced may not always be reflected in the assessment in the way you expect.

Why has my EPC rating gone down?

People are sometimes surprised when a new EPC produces a different result from an older certificate even though they haven't made the property worse.

There are several possible reasons.

The property may have been assessed differently, better information may now be available, an earlier assessor may have recorded something differently, or the assessment methodology itself may have changed.

Government methodology for energy assessments is periodically updated, and further reforms to EPCs are currently being developed.

So an old EPC should not always be treated as a guaranteed prediction of what your next assessment will show.

What doesn't directly determine your EPC?

There are also plenty of things that homeowners assume affect an EPC but generally aren't what the assessment is trying to measure.

For example, your score is not simply based on:

• how much energy you personally use
• how high you set the thermostat
• whether you turn lights off
• how many people live in the property
• how expensive your energy tariff is
• how clean or well decorated your home is
• whether your kitchen or bathroom is modern

An EPC assesses the energy characteristics of the property, rather than judging the habits of the current occupants. Government EPC statistics likewise describe ratings as estimates based on property characteristics.

Which improvements are most likely to improve my EPC?

There isn't one answer that applies to every house.

Depending on the property, improvements might include:

1. adding loft insulation
2. improving wall insulation
3. upgrading the heating system
4. improving heating controls
5. replacing inefficient glazing
6. installing renewable energy
7. improving hot-water efficiency
8. upgrading inefficient lighting

But don't automatically start with the most expensive work.

Your existing EPC normally includes recommended improvements and an indication of the property's potential rating.

That can give you a much better starting point.

Should I improve my EPC before selling?

Potentially, but it depends on the improvement.

Spending thousands of pounds solely to increase an EPC by one or two points may not make financial sense immediately before selling.

On the other hand, relatively simple improvements could be worthwhile, particularly where they:

• move the property into a higher EPC band
• make the house cheaper to run
• address something buyers are likely to question
• make the home more attractive compared with similar properties
• remove uncertainty about the property's energy performance

The first step is understanding where your current rating comes from.

Check your EPC before your buyer does

Your EPC is one of the pieces of information a buyer can see about your property before they commit to purchasing it.

So don't discover a problem at the same time they do.

Tepilo helps you get your property information together earlier, understand what's already known about your home and identify areas that may need attention before they become part of the transaction.

Find your property's EPC, check what's recorded and start getting your home ready to sell with Tepilo.