How do you retrofit a home and how much will it cost?

You might have heard it referred to as retrofitting, making energy efficiency improvements, or making a home greener.

All of these terms are different names for making changes to older buildings, in order to make them more energy efficient. Better energy efficiency means a home uses less energy to run it, as well as lower energy bills. Plus, being less reliant on fossil fuels means it will emit less carbon into the atmosphere.

Here, we look at how retrofitting works, how much it costs, and how much you could save in the long term. As well as why retrofitting matters, and how it’s the pathway to a greener, more sustainable future for all of us.

What is retrofitting?

New-build homes are constructed with energy efficiency in mind, with features like A-rated condensing boilers installed as standard, and good insulation.

But lots of UK homes are decades, or even centuries old, and built at a time when energy efficiency wasn’t a concern for housebuilders. Going back to this older housing stock, and making improvements that result in greener, more energy efficient homes, is the thinking behind retrofitting.

In simple terms, retrofitting is all about making older buildings work smarter, not harder. This could be by replacing your old gas boiler with a more energy efficient heat pump, improving your insulation to reduce heat loss from your home, or adding solar panels to your roof, so you can generate your own electricity, rather than drawing it from the grid.

Within your home’s Energy Performance Certificate, you’ll find its current energy efficiency rating, as well as the potential score it could reach if all of the recommended improvements are made. Making these changes is known as retrofitting: all with the goal of making homes cleaner, greener, and cheaper to run.

Why is retrofitting needed, and what are the challenges?

According to the UK Green Building Council, 80% of homes around today will still be lived in in 2050. Right now, we have some of the oldest and leakiest homes in western Europe. So retrofitting is a big part of making sure our homes are comfortable places to be, and that they can run sustainably.

But making a home greener will need to fit with, and complement, the building’s existing design, and layout. So, how to make a property more energy efficient, and the best retrofitting route, will differ from one home to the next.

If your home has a valid Energy Performance Certificate in place, it will detail the improvements you could consider making to improve its energy efficiency rating.

The average energy efficiency rating is D, and less than half of all homes across England are currently rated EPC band C or above. While that means there are many energy inefficient homes around at the moment, it also means there’s lots of opportunity to make green improvements.

But in many cases, the cost of improvements is a big barrier to making changes.  Homeowners often don’t invest in green improvements because they don’t plan in living in the home long enough to truly reap the rewards and savings offered by energy efficient upgrades. Our 2023 analysis showed that almost half of homeowners don’t plan to make green improvements for this reason.

Additionally, many homeowners don’t know which improvement is the best to make, or where to start. Research we conducted in 2023 found that just 4% of homeowners plan to have a heat pump installed in their home, despite their being government grants available to help towards the cost.

How could my home benefit from retrofitting?

Retrofitting a home has a range of potential benefits, both immediate and long term:

• Lower bills: Homes that retain heat better and have more efficient heating systems as a result of retrofitting will require less energy to keep them warm. Energy bills have fallen since their peak in 2022, and are set to fall again from April 2024. But they’re still nearly double what they were back in February 2021
• Better for the planet: Greater efficiency doesn’t just mean you’ll spend less on bills. Burning less fossil fuel to power your home will also mean lower carbon emissions
• A more comfortable environment: Improvements like better insulation will stop your home from feeling cold and draughty in the winter, and overly hot in the summer. The result? More stable, comfortable temperatures the whole year through
• Increased property value: Our research shows that a property moving from an EPC rating of F to C could increase the home’s value by 15%, on average

What kind of things could I retrofit in my home?

There are lots of different changes you can make that would be classed as retrofitting, and they vary in terms of cost, effort, and disruption you can expect them to cause. Smaller scale improvements might include draughtproofing, and changing older halogen lightbulbs for new LED versions. While bigger, more costly options might include installing thicker loft insulation to keep in heat in the winter, and stop cool air escaping during summer. Or switching an old, inefficient gas boiler with a low-carbon alternative, such as a heat pump.

Some of the retrofit options available include:

• Upgrading to energy-efficient lighting: Replacing traditional or halogen lightbulbs with energy efficient LEDs
  
• Installing double or triple glazing, or adding secondary glazing: Replacing single-glazed windows with A-rated double glazing or triple glazing, or adding secondary glazing to existing single-glazed windows
  
• Adding cavity wall Insulation: Cavity walls are the easiest to insulate, with insulants injected into the cavity from the outside
  
• Adding solid wall insulation: It’s still possible to insulate solid walls, but this will need to be added either internally, or externally
  
• Adding or upgrading loft insulation: The recommended minimum depth for loft insulation is 270mm. So while your home may have some insulation in the roof or loft, it’s worth checking that it reaches this depth. Topping up from 120mm to at least 270mm of insulation can reduce annual carbon emissions by 55kg annually. It’s worth noting that of all the different ways of insulating a home, loft and roof spaces are the most affordable improvements, and the easiest to carry out
  
• Adding floor insulation: Around 8% of heat is lost through the floor in an uninsulated home. And this figure rises if you have an insulated roof and walls
  
• Installing renewable energy systems: Installing alternative energy solutions such as solar panels means households can generate their own electricity. And in some cases, sell unused power back to the grid
  
• Switching to a low or no-carbon heating system: Air source or ground source heat pumps are no-carbon alternatives to gas boilers. You could also replace an inefficient gas boiler, such as a G-rated version, with an energy-efficient A-rated condensing boiler. While this option still uses gas to heat a home, a newer, more efficient version will use considerably less power to keep your home warm, and your water hot

How much does retrofitting cost, and how much could I save?

There’s no one-size-fits-all retrofit, and the costs of making green improvements will vary based on the type of home you live in. And a change that might work for one home may not work for another. For example, if you have a thatched roof, it wouldn’t be possible to install solar panels. You might also be able to reduce costs by carrying out works at the same time as making other home improvements.

The average cost of a heat pump will vary based on the size of your home. The government estimates that an air source heat pump will cost around £12,000 on average.

Energy Saving Trust estimates that a ground source heat pump (that’s buried in trenches) to cost around £28,000. And this could rise to £49,000 if you need to dig a borehole. Government grants of £7,500 are available to put towards the cost of heat pumps.

The average domestic solar PV system is 3.5kWp and costs around £7,000. Read more about the cost of solar panels here.

Depending on the wattage and style, energy-saving light bulbs can cost from around £2.50, up to £12.

The cost of insulating a home vary, depending on the type of insulation you choose. Assuming we’re insulating a semi-detached house, installation costs could be around £2,700 for cavity wall insulation, £930 for roof insulation, £7,500 for internal solid wall insulation, and £12,000 for external solid wall insulation.

A set of A-rated double-glazed windows costs around £15,000 to install in a semi-detached property.

Energy Saving Trust lays out some potential costs and savings below:

Change made	Average one-off cost	Average bill saving (annually)
Insulating hot water pipes	£1.75 per metre	£6
Switching to energy-efficient light bulbs	Approx £2.50 – £12 per bulb	£65
Adding loft insulation to a semi-detached house (from 0mm to 270mm)	£930*	£270
Upgrading G-rated gas boiler to heat pump in a semi-detached house	£14,000*	£340
Upgrading single glazing to A-rated double glazing in a semi-detached house	£15,000	£165
Upgrading G-rated gas boiler to A-rated gas boiler	£3,700	Up to £580
Adding solar panels (and using the Smart Export Guarantee)	£7,000	Up to £545
Adding internal solid wall insulation to a semi-detached house	£7,500	£380

Are there any grants available to help with retrofitting?

If you’re considering making green improvements to a home you live in now, or one you might move to in the future, there are government grants and schemes available to help towards the cost. Take a look at some of the current green incentives available to households.