What is Retrofit?
Refurbishment and retrofit are often used interchangeably. While they are siblings within the same family, and can absolutely be carried out in parallel, they are two distinct actions, and understanding the difference is key in taking up ownership over what options you have in regards to upgrading your home.
As a simple analogy, retrofit and refurb can be thought of as types of surgery - refurbishment as cosmetic surgery and retrofit as medical surgery. Refurbishment improves the surface, layout and appearance of a home; retrofit goes deeper addressing building fabric, insulation, structure, airtightness and thermal efficiency. So while retrofit might not be as glamorous as refurb, it can address deeper thermal or structural parameters relevant to your home and improve the comfort and resilience of your home. Tackling both at the same time can be a good way to make the process more efficient, minimise cost and create a healthy and beautiful home all in one!
Throughout this blog post, I aim to shed light on retrofit for homeowners, deepening understanding of how retrofit measures can be integrated into a refurbishment project, while also highlighting small, achievable changes that empower you to improve the thermal comfort of your home, reduce your energy bills and create a more sustainable, healthier place to live.
If sustainability is important to you (and it should be), I will also explain the difference between two key terms - embodied carbon and operational carbon and how you can reduce both. Understanding these concepts before starting a house refurbishment allows sustainability principles to be embedded alongside design intent - from that very first design meeting through to completion.
Why Retrofit Matters Now
The magical thing about retrofit is that it aligns your interests as a homeowner in having a happy, healthy home and lower energy bills - with the UK’s sustainability goals at large. The UK has legally binding carbon budgets on the path to net zero by 2050 and the UK’s 25 million existing homes contribute to approximately 18% of the nation’s carbon emissions and consume around 30% of the country’s energy. (1) Crucially, most of the buildings that will exist in 2050 already exist today(2). This makes refurbishment and retrofit one of the most powerful tools we have to reduce emissions at scale. Delaying retrofitting while the grid decarbonises only increases whole life carbon making the next decade a critical window for addressing retrofit in the built environment. (3)
Figure 1. Total number of UK dwellings broken down by their space heating demand, showing the transition required from existing levels of high demand to the LETI retrofit target range. Figure based on stock modelling carried out by LETI.
Operational Carbon
Operational carbon refers to greenhouse gas emissions associated with the day-to-day running of a building, e.g. by electricity, gas, or other fuels.
As the national grid decarbonises, ie. transitioning away from fossil fuels towards renewables and nuclear, operational carbon will inevitably decrease. The next few years are therefore crucial: decisions made now should support this transition and future-proof homes for a low carbon energy system.
Replacing your boiler today with another gas boiler would mean:
You continue emitting operational carbon due to gas
There is embodied carbon associated with manufacturing and installing the boiler
Whilst gas boilers are not banned yet, the UK government is planning to phase them out which creates some unpredictability
It’s important to have a ‘whole house’ approach for each case, as each building is different and comes with its own bespoke set of existing conditions. A whole-house approach will maximise energy savings and balance issues of moisture, comfort and heat. For example, if a heat pump was installed without reducing the energy demand of a building first, the energy bills would get higher as electricity is currently more expensive than gas.
Figure 2. Performance-oriented retrofit. Shifting in favour of better performing retrofit, with wide-ranging systemic impacts. Illustration by Dark Matter Labs ‘Scaling the Right to Retrofit’ https://provocations.darkmatterlabs.org/scaling-the-right-to-retrofit-3b74aa6b08ad
Embodied Carbon
Embodied carbon accounts for the greenhouse gas emissions generated across the entire lifecycle of construction materials - including extraction, manufacturing, transportation, installation, maintenance and eventually demolition.
Here, sustainability requires balance: the carbon required to produce the material must be weighed against its durability and lifespan. For example, many concrete buildings constructed over 50 years ago, such as the National Theatre by Denys Lasdyn, can arguably be considered sustainable despite concrete’s high embodied carbon. Their longevity has effectively ‘locked in’ that carbon, and demolition is unlikely.
Some natural materials such as timber and cork, go a step further by sequestering carbon, which means they absorb CO2e from the atmosphere and store it long term. Stone, a material currently having a resurgence, has a long history in UK construction, excellent compressive strength and 75% lower embodied carbon than brick, making it a compelling low-carbon material that comes in varying forms and sizes, including in brick form.
Whole Life Carbon
Whole Life Carbon considers both embodied carbon and operational carbon across the entire lifespan of a building. Achieving low whole life carbon requires a delicate interplay between
Low embodied carbon material specifications
Reduction of heat loss through well-detailed and well-insulated fabric
Minimising draughts through airtightness and upgraded windows and doors
Introduction of renewable technologies - heat pumps or PV
Timing is critical when thinking about whole life carbon. In some cases, the embodied carbon cost of replacing a building element before the end of its useful life can outweigh the operational carbon savings. A whole-life approach helps identify when to upgrade, and when it’s better to wait.
Figure 3. Potential retrofit steps in a Victorian terraced house. Illustration taken from Part 2a Victorian House: A retrofit guide for residents, ESSA local conservation association website: https://files.websitebuilder.prositehosting.co.uk/ae/fc/aefc33f7-d928-4a7c-88d1-a29bf28b3e57.pdf
The Low Hanging Fruit
If you are planning to refurbish your house, this is a great opportunity to tackle those low-hanging fruit that can make your home slightly more thermally efficient.
If you’re demolishing walls and adding an extension, specifying lower-carbon materials such as stone or timber, and minimising the amount of steel used, can meaningfully reduce embodied carbon.
Designing new wall build-ups with natural, breathable insulation - and exceeding Part L U-value requirements reduces heat loss. This, in turn, allows for:
Smaller radiators or heat pumps
Reduced renewable system sizes
Lower capital and running costs
Taking a whole-house approach also means upgrading the existing fabric where possible. Loft insulation, in particular, is one of the most effective and affordable interventions, as a significant proportion of heat is lost through the roof.
Replacing single-glazed windows at the end of their life with double-glazed units can dramatically improve comfort - but only when replacement is genuinely necessary. Where windows and doors are serviceable, draught-proofing can make a noticeable difference. Where possible, avoid aluminium frames, which tend to have higher embodied carbon and poorer thermal performance.
Finally, it’s important to remember as homes become more airtight, ventilation becomes essential. Without adequate ventilation, moisture, condensation and mold can develop. A well-designed retrofit always balances airtightness with healthy indoor air quality. Installing an MVHR can help bring fresh air into your home without bringing in cold draughts.
Figure 4. Proportion of heat loss in a home. Illustration taken from Part 2a Victorian House: A retrofit guide for residents, ESSA local conservation association website: https://files.websitebuilder.prositehosting.co.uk/ae/fc/aefc33f7-d928-4a7c-88d1-a29bf28b3e57.pdf
Renewables: The Final Step
By retrofitting your home first, reducing heat demand through insulation and air tightness, and then installing an air source heat pump, you avoid unnecessary future replacement costs, take advantage of available grants and lower your energy bills from day one. Whilst the upfront cost of installation is a factor to take into account, replacing a gas boiler with a low carbon technology such as a heat pump can save a four bedroom house up to £1,300 annually on heating bills.
Combining retrofit steps with refurb
For a private residential extension, key ‘trigger points’ within the extension and refurbishment can act as ways to lock in retrofit measures, in accordance with Part L in the Building Regulations which mandates that when a specific part of the building is renovated, it must be upgraded to improve their thermal efficiency to meet specified U-values. This allows incremental progress towards energy efficiency without requiring immediate full-scale retrofits, making it accessible for a broader range of budgets and hitting two birds with one stone.
Combining retrofit steps alongside your refurb also helps reduce the mess and disruption. Whilst you already are pulling up floorboards and ceilings, why not add in some MVHR ducting or insulation? The phasing of the retrofit steps can and should absolutely run in parallel with your refurbishment.
Ultimately, the most efficient approach is to treat refurbishment and retrofit as partners. By capitalising on natural ‘trigger points’ during a renovation you can significantly reduce disruption and cost. This integrated strategy allows you to lock in energy efficiency immediately ensuring your home is not only aesthetically updated but also future-proofed against rising bills and ready for a low-carbon future.
by Constantina Antoniadou
(1) London Energy Transformation Initiative (LETI), Climate Emergency Retrofit Guide (London: LETI, 2020), 18, accessed September 18, 2024, https://www.leti.london/retrofit.
(2) London Energy Transformation Initiative (LETI), Climate Emergency Retrofit Guide (London: LETI, 2020), 18, Accessed February 02, 2026, https://www.leti.london/retrofit.
(3) Whole Life Carbon Study: Five Lewisham Primary Schools - Retrofit vs Demolition. Retrofit Action forTomorrow for the UK Department for Education, September 2023, 42
(4) UK Gas Boiler Ban - In Effect from 2025 or 2035? https://www.greenmatch.co.uk/boilers/gas/ban
(5) Ministry of Housing, Communities & Local Government, Approved Document L: Conservation of Fuel and Power, Volume 1, Dwellings, 2021 edition incorporating 2023 amendments, Section 11.
U-values are a measure of how effective a material is as an insulator. For more information read our other blogpost: https://www.mwarchitects.co.uk/ask-the-architect/2024/5/3/what-is-a-u-value
(6) MVHR’s are an energy-efficient, whole-house ventilation system that provides constant, filtered fresh air while recovering up to 96% of heat from exhaust air. It removes moisture and pollutants to improve indoor air quality, making it ideal for airtight new builds. The system reduces heating bills by recycling warmth back into the home.