‘Without retrofitting, we won’t reach net zero’: can we make our homes carbon neutral by 2050? | Reimagining sustainability

Last year the issue of home insulation became an urgent national topic. It began when Insulate Britain activists blocked several of England’s major motorways. Protesters were imprisoned (one went on hunger strike), and a passionate national debate ensued about the tactics used by the campaign group.

But whether you approve of its methods or not, the problem remains that the UK has some of the oldest, leakiest – and, as such, least energy-efficient – housing in Europe.

Meanwhile, pre-pandemic, the building sector as a whole accounted for 38% of all global energy-related CO₂ emissions – that includes emissions from operating buildings and from construction, according to the UN’s environment programme.

“Because that’s such a large proportion of global emissions, there is a significant opportunity to make a big difference – and decarbonising buildings can be a major part of the solution, but it won’t be as easy as it sounds,” says zero-carbon pioneer Prof Ljubomir Jankovic, director of the Centre for Future Societies Research and founder of the Zero Carbon Lab at the University of Hertfordshire.

In the UK, the main focus needs to be houses that have already been built, says Jankovic, because they will make up 80% of the housing stock in 2050 – the year the government has pledged to achieve net zero.

“That’s 19.1m homes in total that will still be in use – but most aren’t energy efficient, so retrofitting is an essential step,” says Jankovic. “From my calculations, there are more than 10,000 days between now and 2050, so we need to retrofit approximately 1,870 houses per day to reach that goal. That puts the scale of effort required into perspective.”

For some properties, retrofitting, or installing new facilities or systems, might include improved insulation and making properties more airtight; for others, it could require the addition of heat pumps, solar panels and, in the near future, a new type of hydrogen boiler. “Without retrofitting, we won’t reach net zero by 2050,” says Jankovic.

New buildings may also be adding to the challenge. “At the moment, building regulations don’t require new builds to be net zero, so we are contributing to the number of houses that will need retrofitting, even though some are new.”

One major factor to consider is the embodied carbon emissions within conventional building materials such as brick and concrete – that’s the carbon emissions involved in making the material, transporting it to site and using it in construction.

Jankovic and his team at the Zero Carbon Lab, a centre that collaborates with government bodies, local authorities and industry, have calculated that bricks have embodied emissions of about 357kg CO₂ per cubic metre, while a cubic metre of concrete is about 10 times higher.

“Although these embodied emissions are not always taken into account, they all end up in the atmosphere and add to the challenge of controlling climate change,” says Jankovic. It will take way beyond 2050 to reach net zero if these materials continue to be used without consideration for their embodied emissions, he says, even with the addition of renewable energy systems and energy-efficient retrofitting.

But there is another low-carbon option. Jankovic’s research shows that using biosourced materials that can reduce the starting embodied emissions, such as hempcrete or hemp lime instead of brick, could help to reach net zero by 2045 in new builds, in concert with other net zero design strategies. In his view, new research is required in order to update reference information on embodied emissions in other biosourced materials, such as straw bale, timber and others, which “sequester” carbon from the atmosphere during the plant growth period. Currently, this information is not readily available for designers.

Working with Welwyn Hatfield borough council in Hertfordshire, Jankovic’s research into zero carbon building design is helping the authority to reduce the cost of powering buildings with renewable energy, improve insulation and opt for greener building materials. He is also assisting Stevenage borough council to evaluate how best to get to net zero by 2030.

Using advanced modelling and simulation of dynamic heat transfer, Jankovic and his team can calculate the emissions of a building over a specific time period, based on hourly weather data gathered over a year – that’s 8,760 sets of data, whereas simplified methods based on 12 monthly average sets of data and steady state heat transfer gave far less accurate results. This larger volume of data makes a difference, allowing for more rigorous analysis. “We need to quantify everything, from the starting emissions to ongoing emissions, and ‘pushing and poking’ these computer models in a structured way helps us to determine how we get to zero,” he says.

Jankovic is working on making these technical methods accessible to councils and local authorities so they can use preset designs to achieve net zero with more confidence. Ultimately, change happens at the design stage before a new build or a retrofit.

“Everyone needs to understand what it means to design net zero emissions buildings – presently, industry doesn’t have enough people who are qualified to do net zero design that’s based on rigorously tested performance data,” he says. “But if we really want to get serious about reaching net zero we need to improve the skills across the industry and to all pull together, from developers to construction workers, to planners, architects and building performance modellers, to create a critical mass of new professionals capable of designing and delivering buildings with a certainty of performance outcomes.”

Find out more about the game changing multi-disciplinary research at Herts, how it is deepening understanding of climate change and helping to tackle the environmental emergency.