Written by Stuart Elmes.
How has the change to building regulations in England driven solar uptake?
In 2021, the Building Regulations Part L (Conservation of Fuel and Power) in England were updated to include solar PV as part of the target specification, a move that was widely expected to drive a rapid increase in the uptake of solar PV by housebuilders. When the Scottish government made similar changes to its regulations in 2015 this eventually fed through into solar being on around 80% of all new homes built there.
A new statistical data set published by the UK Ministry of Housing, Communities and Local Government (MHCLG) gives us the clearest picture yet of how the transition to the new regulations has played out and how many homes in England are now being built with solar PV.
Energy efficiency characteristics of new dwellings
The data is based on the submission of an Energy Performance Certificate (EPC) at completion of the home. The EPC lists the type of property (flat, house bungalow) and the energy technologies present. From the version of the software used to create the certificate it is possible to see what version of the Building Regulations the house was built to.
An important point to note in relation to this data set is that it includes change of use as well as new build projects. The number of properties is higher than other data sets that monitor new build housing activity, and the proportion of apartments is much higher – around 40% of the total, compared with around 18% for new buildings.
The Timing of the Transition
The rules which governed how the new regulations would come in, the transitional arrangements, were changed for Part L 2021. As before, the new regulations would be applied to whole building sites based on the date on which planning consent was applied for. In addition, the new regulations would sweep up individual houses that commenced construction after a second deadline. The idea was to speed up the transition so that we didn’t have homes being built to old regulations many years in the future.
The planning deadline was 15th June 2022 and the commencement deadline was 15th June 2023. So in theory all new homes being built two years after the regulations came into force should be to the new regulations.
The data shows us that this did not happen. In fact, it was not until mid-2024 that the proportion of new homes completed to the new regulations really started to ramp up. Even by the end of 2025, the proportion of homes completed that were to the new regulations had only reached 65%.
There are two factors that explain why the changes made to the Transitional Arrangements did not result in a faster take-up.
First, developers worked hard to get as many houses commenced on site before the deadline as possible. Drainage was put in, footings were dug and concrete foundations were poured so the house could be classed as commenced. These so-called ‘technical starts’ tied up working capital for housebuilders but the pay-off was more homes built to older, lower-cost building regulations. A slow-down in housebuilding then stretched out the stock of commenced houses even further as building rates reduced.
Second, as previously mentioned the data set also includes buildings undergoing a change of use to become housing. These projects are often more complex and time consuming – think of a project to reconfigure a city-centre office block into apartments. Such projects completing today are likely to have started many years ago under the previous regulations.
The new data set also allows us to unpack the transition by house type. We can see that at the end of 2025 only 40% of new flats were being built to Part L 2021.
When you look at the same data for houses and bungalows, the transition has run much more quickly. At the end of 2025 over 80% of new houses were being completed to Part L 2021. If you timeslip the data forward 3 months for roofing works, then we are at around 90% of houses now being roofed are under Part L 2021.
How Many Homes Have Solar?
The EPC dataset also tells us what technologies have been used. The chart below shows the proportion of houses and bungalows completed under Part L 2021 each month that had solar PV or heat pumps or both technologies fitted.
After an initial period based on thin data, the proportions have stabilised in 2024 at around 65% of homes with solar only and a further 10% with both solar and heat pump fitted. Around 20% of homes are built with only heat pump, and a remainder of 5% that has neither technology.
The corresponding value for flats built under Part L 2021 with solar panels is currently at around 45%.
New Build Housing is Now a Significant Proportion of all new UK Solar Installations
Putting all of this together, we can say that for houses and bungalows the transition to Part L 2021 is pretty much done. Flats and apartments have further to go but a lower proportion of these have solar.
Even as the total number of dwellings being completed has fallen, the number of new homes built in England with solar has risen from around 2,500 a month in 2023 to around 8,000 a month today, driven by the change to building regulations.
The MCS data dashboard has the number of MCS registered installations in England running at around 16,000 per month since the beginning of 2025, which suggests that new build housing now accounts for half of all solar installations.
What Comes Next?
The Future Homes Standard is the next big change in energy efficiency regulations coming towards housebuilders in England. It will make solar PV a mandatory functional requirement for new homes rather than a tradeable component of the target specification as it is now.
We can expect it to result in an even higher proportion of homes being built with solar than is the case under Part L 2021, and the number of solar panels on each house is likely to increase significantly.
You can find out more about how the Future Homes Standard solar provision is calculated in my earlier blog here.