Category: Ecology

Introduction: The Carbon Question in Retrofit Projects

In discussions about sustainable construction, the focus often falls on operational energy—how much electricity a building consumes and how efficiently it can be heated or cooled. This is important, of course, but embodied carbon is another equally pressing issue. Unlike operational emissions, which accumulate over time, embodied carbon is released immediately during building materials’ production, transport, and installation. In other words, these emissions immediately impact climate change, making material choices a crucial consideration in any retrofit or new construction project.

At Unagru Architecture Urbanism, we have spent years researching how to reduce the carbon footprint of buildings, particularly in retrofits. One clear conclusion is that electrification is a major step forward, particularly when powered by renewable energy. However, once heating and energy use are optimised, we must focus on the materials used in the construction process.

Our Approach to Reducing Embodied Carbon

Our strategy for minimising embodied carbon follows a clear hierarchy. First, we prioritise intelligent design to preserve and adapt what is already there—because the greenest building material is the one that doesn’t need to be produced at all. Second, we focus on reusing, recycling, and upcycling materials, making the most of what is already available to reduce waste and avoid the emissions of new production. Now, we are expanding our research into materials that are more difficult to recycle but significantly impact a building’s overall carbon footprint.

This brings us to screed—a seemingly minor component of a floor, but one with a surprisingly large carbon footprint. The industry standard is cement-based screed, but limecrete is a viable alternative. How do these two options compare in terms of cost and carbon emissions? And does using a low-carbon material like limecrete make more sense than relying on carbon offsetting?

Understanding Screed and Its Role in a Building

Screed is a layer of material applied over a reinforced concrete floor slab to create a smooth and even surface for the final floor finish, whether it be timber, tiles, or carpet. It also plays an important role in thermal mass, meaning it helps to regulate temperature by absorbing and releasing heat slowly. This is particularly useful when underfloor heating is installed, as a good screed will help distribute heat efficiently throughout a room.

Most screeds used today are made from cement, sand, and water, forming a dense, strong, and durable layer. However, cement production is one of the largest single contributors to global carbon emissions, responsible for around 8% of total CO₂ emissions worldwide. This makes any effort to replace cement-based materials with lower-carbon alternatives a priority for sustainable construction.

Limecrete, a mixture of hydraulic lime, aggregate, and water, is one such alternative. Historically, lime-based materials were used widely before cement became dominant in the 19th and 20th centuries. Unlike cement, lime allows buildings to “breathe” by regulating moisture levels, reducing the risk of trapped damp and condensation. More importantly for sustainability, limecrete has a significantly lower carbon footprint than cement screed.

 Cement Screed vs. Limecrete: A Comparison

A Brief History of Lime and Cement in Construction

The use of lime in construction dates back thousands of years. The Romans, renowned for their engineering, used lime-based mortars and concretes in their vast network of roads, aqueducts, and buildings. One of the most famous examples of lime-based construction is the Pantheon in Rome, completed in 126 AD, which features the world’s largest unreinforced concrete dome—still standing today. The secret to its longevity lies in the volcanic ash and lime mix, which gave it both strength and self-healing properties when exposed to moisture.

Throughout the Middle Ages, lime remained the dominant binding material for construction across Europe. Traditional timber-framed buildings in England, France, and Germany used lime plaster and limecrete floors, valued for their breathability and flexibility. In Venice, builders developed a version of hydraulic lime—pozzolanic lime—that could set underwater, enabling the construction of structures that could withstand the city’s unique lagoon environment.

Cement, on the other hand, is a much younger material in comparison. While rudimentary forms of hydraulic cement date back to Roman times, modern Portland cement was only patented in 1824 by Joseph Aspdin, a British bricklayer from Leeds. Aspdin discovered that burning limestone and clay together created a material that, when ground into a fine powder and mixed with water, set much faster and harder than traditional lime mortars. By the late 19th and early 20th centuries, cement had largely replaced lime in construction due to its superior compressive strength and quick setting time.

This transition was accelerated by the Industrial Revolution, when the demand for rapid, large-scale construction made cement the preferred choice. The development of reinforced concrete in the late 19th century—pioneered by François Hennebique and later perfected by August Perret and Le Corbusier—further cemented (pun intended) the material’s place as the default choice for modern buildings.

By the mid-20th century, lime had almost disappeared from mainstream construction, relegated to heritage restoration and niche applications. However, in recent years, a renewed focus on sustainability, breathability, and carbon reduction has led architects, engineers, and builders to rediscover the benefits of lime-based materials.

The transition from lime to cement has had lasting consequences, some of which were only fully understood decades later. A striking example comes from the conservation of historic buildings. Many post-war renovations used cement-based mortars and plasters to repair old buildings originally constructed with lime. The result? Severe damp problems, as the non-breathable cement trapped moisture inside historic masonry, leading to accelerated decay. Conservation specialists now spend millions annually removing cement-based materials from historic buildings and replacing them with lime.

The Pantheon’s lime-based concrete has survived for nearly 2,000 years, while many mid-20th-century reinforced concrete buildings are already deteriorating due to corrosion of the steel reinforcement inside them. Scientists studying ancient Roman construction techniques are now looking at pozzolanic lime-based materials as a way to create more durable, sustainable concrete in the future.

Characteristics and Differences: Lime Screed vs. Cement Screed

With this history in mind, how do lime screed and cement screed compare in modern construction? While both serve the same basic function—creating a smooth, level surface for flooring—they differ significantly in composition, performance, and environmental impact.

1. Composition and Chemical Properties

     •           Cement screed is made from Portland cement, sand, water, and sometimes additives for faster curing or increased strength. The cement binds the sand particles together, creating a dense, rigid surface.

     •           Lime screed consists of hydraulic lime, aggregate (such as sand or crushed stone), and water. Unlike cement, which hardens by a chemical reaction with water (hydration), lime sets through a slow carbonation process, absorbing CO₂ from the air. This makes limecrete more breathable and flexible.

2. Strength and Durability

     •           Cement screed is extremely strong in compression, making it ideal for heavy loads and high-traffic areas. However, it is also brittle—once set, it does not accommodate movement well, leading to cracking if the substrate shifts or expands.

     •           Lime screed is more flexible, which means it can accommodate slight movements in a building without cracking. While its compressive strength is lower than cement’s, it is still sufficient for most residential and office applications.

3. Breathability and Moisture Control

     •           One of the biggest advantages of lime screed is its breathability. It allows moisture to pass through, preventing condensation and trapped damp. This is especially valuable in historic buildings and solid-wall constructions, where excessive moisture retention can cause structural damage.

     •           Cement screed, by contrast, is non-breathable. Once set, it forms a moisture barrier, which can lead to damp issues if not properly managed with membranes and ventilation.

4. Thermal Performance and Underfloor Heating

     •           Lime screed has better thermal mass properties, meaning it retains and gradually releases heat over time. This makes it an excellent companion to underfloor heating systems, as it helps maintain a stable indoor temperature.

     •           Cement screed heats up and cools down more quickly, which can make heating systems slightly less efficient in terms of maintaining a steady warmth.

5. Setting Time and Construction Logistics

     •           Cement screed sets quickly, often within 24–48 hours, and reaches full strength in a few weeks. This makes it ideal for fast-track construction projects where time is a priority.

     •           Lime screed takes much longer to cure—often several weeks or even months, depending on conditions. This slower process can be a drawback in projects with tight schedules but is beneficial in terms of reducing shrinkage and cracks over time.

6. Carbon Footprint and Environmental Impact

     •           Cement screed has a much higher embodied carbon footprint. Cement production is responsible for roughly 8% of global CO₂ emissions, making it one of the most polluting industries in the world.

     •           Lime screed produces far less CO₂, and because it reabsorbs carbon during the setting process (carbonation), it partially offsets its own emissions. On average, limecrete has 80–90% lower embodied carbon than cement screed.

A CASE STUDY COMPARISON

To assess whether limecrete is a viable alternative, we compared both options in a 100m² office retrofit requiring an 80mm-thick screed layer. We looked at two key factors: cost and carbon impact. At our office, we mistakenly didn’t opt for limecrete, blinded by the fear of long setting times after a protracted completion process robbed us of two months on our construction programme. We now have time to review all our choices and learn for future projects.

1. Cost Comparison

Cement screed is the cheaper option, with an average cost of £15–£16 per square metre. For a 100m² project, this results in a total material cost of around £1,550.

Limecrete, by contrast, is more expensive, typically costing between 1.5 to 2 times more than cement screed. This means the total material cost rises to £2,325–£3,100 for the same 100m² area.

While limecrete does come at a premium, its benefits extend beyond cost alone. To determine whether the extra expense is justified, we must examine its environmental impact.

2. Carbon Impact Comparison

The key reason to consider limecrete over cement screed is its significantly lower embodied carbon. Cement-based screed has an estimated embodied carbon of 100 kg CO₂e per tonne, meaning a typical 100m² floor using 17.6 tonnes of cement screed will produce around 1,760 kg of CO₂ emissions.

Limecrete, on the other hand, has an embodied carbon of just 13.58 kg CO₂e per tonne, meaning a 14.4-tonne application would generate only 195.5 kg of CO₂ emissions.

The difference is stark: switching to limecrete reduces the project’s carbon footprint by over 1,500 kg of CO₂e, an almost 90% reduction in emissions from screed alone.

Carbon Offsetting vs. Low-Carbon Materials

When discussing embodied carbon, a common counterargument is that emissions can be offset rather than prevented. But what does this actually mean?

Carbon offsetting is a method of compensating for emissions by funding projects that reduce or absorb an equivalent amount of CO₂ elsewhere. These might include reforestation schemes, renewable energy projects, or carbon capture technologies.

Offsetting has become popular because it allows companies and individuals to “neutralise” their emissions without having to make substantial changes to their materials or processes. However, there are two major concerns with this approach:

        1.      Uncertainty in Carbon Offsets – Not all offset projects deliver the promised reductions. Some forests planted as carbon sinks are later destroyed by fire or logging, and some renewable energy projects would have happened anyway without the offset funding. This means that while the offset exists on paper, it does not always represent an actual reduction in atmospheric CO₂.

        2.      Timing of Emissions – Embodied carbon is released immediately, whereas offsets often take years or even decades to absorb the equivalent amount of CO₂. A tree planted today will take 40 years to capture the carbon emitted by cement production today. Meanwhile, climate change continues to accelerate.

If we compare the cost of using limecrete to the cost of offsetting, the numbers are revealed.

     •           The extra cost of limecrete is approximately £1 per kilogram of CO₂ saved.

     •           The cost of voluntary carbon offsets varies but typically ranges from £4 to £30 per tonne of CO₂e (or £0.004 to £0.03 per kilogram).

     •           At these prices, offsetting the 1,760 kg CO₂e emissions from cement screed would cost only £7–£52—far less than the additional £775–£1,550 required to use limecrete.

At first glance, this suggests that offsetting is far more economical than switching materials. However, given the growing scrutiny of offsetting schemes and the fact that offset prices are expected to rise dramatically as climate policies tighten, the long-term viability of this strategy is questionable.

More importantly, preventing emissions is always preferable to compensating for them later. Once carbon is released into the atmosphere, it contributes to climate change immediately. Using low-carbon materials like limecrete directly reduces emissions at the source, rather than relying on uncertain future offsetting mechanisms.

Is Limecrete Worth the Extra Cost?

Cement screed remains the cheaper option for projects with tight budget constraints. However, for those committed to reducing embodied carbon in a meaningful and verifiable way, limecrete offers a proven, immediate, and measurable reduction in emissions.

Additionally, limecrete provides other practical advantages beyond carbon reduction. It is more breathable, reducing the risk of trapped moisture and improving indoor air quality. It is also more flexible than cement, making it less prone to cracking over time. These properties may extend a building’s lifespan in specific contexts, further contributing to sustainability.

Ultimately, the choice between cement screed and limecrete comes down to priorities. If reducing carbon emissions in construction is a serious goal, then switching to limecrete is a real and effective step forward—even if it comes at a higher initial cost.

Final Thoughts

The discussion of sustainability in construction often focuses on high-tech solutions, but sometimes, the best answer is simply using better materials. Swapping cement screed for limecrete is a small change that drastically reduces embodied carbon—something that is not always true for other sustainability strategies.

Choosing materials with lower embodied carbon is one of the most reliable, transparent, and effective ways forward for those looking to make a genuine impact in sustainable construction.

Introduction: The Carbon Question in Retrofit Projects

In discussions about sustainable construction, the focus often falls on operational energy—how much electricity a building consumes and how efficiently it can be heated or cooled. This is important, of course, but embodied carbon is another equally pressing issue. Unlike operational emissions, which accumulate over time, embodied carbon is released immediately during building materials’ production, transport, and installation. In other words, these emissions immediately impact climate change, making material choices a crucial consideration in any retrofit or new construction project.

At Unagru Architecture Urbanism, we have spent years researching how to reduce the carbon footprint of buildings, particularly in retrofits. One clear conclusion is that electrification is a major step forward, particularly when powered by renewable energy. However, once heating and energy use are optimised, we must focus on the materials used in the construction process.

Our Approach to Reducing Embodied Carbon

Our strategy for minimising embodied carbon follows a clear hierarchy. First, we prioritise intelligent design to preserve and adapt what is already there—because the greenest building material is the one that doesn’t need to be produced at all. Second, we focus on reusing, recycling, and upcycling materials, making the most of what is already available to reduce waste and avoid the emissions of new production. Now, we are expanding our research into materials that are more difficult to recycle but significantly impact a building’s overall carbon footprint.

This brings us to screed—a seemingly minor component of a floor, but one with a surprisingly large carbon footprint. The industry standard is cement-based screed, but limecrete is a viable alternative. How do these two options compare in terms of cost and carbon emissions? And does using a low-carbon material like limecrete make more sense than relying on carbon offsetting?

Understanding Screed and Its Role in a Building

Screed is a layer of material applied over a reinforced concrete floor slab to create a smooth and even surface for the final floor finish, whether it be timber, tiles, or carpet. It also plays an important role in thermal mass, meaning it helps to regulate temperature by absorbing and releasing heat slowly. This is particularly useful when underfloor heating is installed, as a good screed will help distribute heat efficiently throughout a room.

Most screeds used today are made from cement, sand, and water, forming a dense, strong, and durable layer. However, cement production is one of the largest single contributors to global carbon emissions, responsible for around 8% of total CO₂ emissions worldwide. This makes any effort to replace cement-based materials with lower-carbon alternatives a priority for sustainable construction.

Limecrete, a mixture of hydraulic lime, aggregate, and water, is one such alternative. Historically, lime-based materials were used widely before cement became dominant in the 19th and 20th centuries. Unlike cement, lime allows buildings to “breathe” by regulating moisture levels, reducing the risk of trapped damp and condensation. More importantly for sustainability, limecrete has a significantly lower carbon footprint than cement screed.

 Cement Screed vs. Limecrete: A Comparison

A Brief History of Lime and Cement in Construction

The use of lime in construction dates back thousands of years. The Romans, renowned for their engineering, used lime-based mortars and concretes in their vast network of roads, aqueducts, and buildings. One of the most famous examples of lime-based construction is the Pantheon in Rome, completed in 126 AD, which features the world’s largest unreinforced concrete dome—still standing today. The secret to its longevity lies in the volcanic ash and lime mix, which gave it both strength and self-healing properties when exposed to moisture.

Throughout the Middle Ages, lime remained the dominant binding material for construction across Europe. Traditional timber-framed buildings in England, France, and Germany used lime plaster and limecrete floors, valued for their breathability and flexibility. In Venice, builders developed a version of hydraulic lime—pozzolanic lime—that could set underwater, enabling the construction of structures that could withstand the city’s unique lagoon environment.

Cement, on the other hand, is a much younger material in comparison. While rudimentary forms of hydraulic cement date back to Roman times, modern Portland cement was only patented in 1824 by Joseph Aspdin, a British bricklayer from Leeds. Aspdin discovered that burning limestone and clay together created a material that, when ground into a fine powder and mixed with water, set much faster and harder than traditional lime mortars. By the late 19th and early 20th centuries, cement had largely replaced lime in construction due to its superior compressive strength and quick setting time.

This transition was accelerated by the Industrial Revolution, when the demand for rapid, large-scale construction made cement the preferred choice. The development of reinforced concrete in the late 19th century—pioneered by François Hennebique and later perfected by August Perret and Le Corbusier—further cemented (pun intended) the material’s place as the default choice for modern buildings.

By the mid-20th century, lime had almost disappeared from mainstream construction, relegated to heritage restoration and niche applications. However, in recent years, a renewed focus on sustainability, breathability, and carbon reduction has led architects, engineers, and builders to rediscover the benefits of lime-based materials.

The transition from lime to cement has had lasting consequences, some of which were only fully understood decades later. A striking example comes from the conservation of historic buildings. Many post-war renovations used cement-based mortars and plasters to repair old buildings originally constructed with lime. The result? Severe damp problems, as the non-breathable cement trapped moisture inside historic masonry, leading to accelerated decay. Conservation specialists now spend millions annually removing cement-based materials from historic buildings and replacing them with lime.

The Pantheon’s lime-based concrete has survived for nearly 2,000 years, while many mid-20th-century reinforced concrete buildings are already deteriorating due to corrosion of the steel reinforcement inside them. Scientists studying ancient Roman construction techniques are now looking at pozzolanic lime-based materials as a way to create more durable, sustainable concrete in the future.

Characteristics and Differences: Lime Screed vs. Cement Screed

With this history in mind, how do lime screed and cement screed compare in modern construction? While both serve the same basic function—creating a smooth, level surface for flooring—they differ significantly in composition, performance, and environmental impact.

1. Composition and Chemical Properties

     •           Cement screed is made from Portland cement, sand, water, and sometimes additives for faster curing or increased strength. The cement binds the sand particles together, creating a dense, rigid surface.

     •           Lime screed consists of hydraulic lime, aggregate (such as sand or crushed stone), and water. Unlike cement, which hardens by a chemical reaction with water (hydration), lime sets through a slow carbonation process, absorbing CO₂ from the air. This makes limecrete more breathable and flexible.

2. Strength and Durability

     •           Cement screed is extremely strong in compression, making it ideal for heavy loads and high-traffic areas. However, it is also brittle—once set, it does not accommodate movement well, leading to cracking if the substrate shifts or expands.

     •           Lime screed is more flexible, which means it can accommodate slight movements in a building without cracking. While its compressive strength is lower than cement’s, it is still sufficient for most residential and office applications.

3. Breathability and Moisture Control

     •           One of the biggest advantages of lime screed is its breathability. It allows moisture to pass through, preventing condensation and trapped damp. This is especially valuable in historic buildings and solid-wall constructions, where excessive moisture retention can cause structural damage.

     •           Cement screed, by contrast, is non-breathable. Once set, it forms a moisture barrier, which can lead to damp issues if not properly managed with membranes and ventilation.

4. Thermal Performance and Underfloor Heating

     •           Lime screed has better thermal mass properties, meaning it retains and gradually releases heat over time. This makes it an excellent companion to underfloor heating systems, as it helps maintain a stable indoor temperature.

     •           Cement screed heats up and cools down more quickly, which can make heating systems slightly less efficient in terms of maintaining a steady warmth.

5. Setting Time and Construction Logistics

     •           Cement screed sets quickly, often within 24–48 hours, and reaches full strength in a few weeks. This makes it ideal for fast-track construction projects where time is a priority.

     •           Lime screed takes much longer to cure—often several weeks or even months, depending on conditions. This slower process can be a drawback in projects with tight schedules but is beneficial in terms of reducing shrinkage and cracks over time.

6. Carbon Footprint and Environmental Impact

     •           Cement screed has a much higher embodied carbon footprint. Cement production is responsible for roughly 8% of global CO₂ emissions, making it one of the most polluting industries in the world.

     •           Lime screed produces far less CO₂, and because it reabsorbs carbon during the setting process (carbonation), it partially offsets its own emissions. On average, limecrete has 80–90% lower embodied carbon than cement screed.

A CASE STUDY COMPARISON

To assess whether limecrete is a viable alternative, we compared both options in a 100m² office retrofit requiring an 80mm-thick screed layer. We looked at two key factors: cost and carbon impact. At our office, we mistakenly didn’t opt for limecrete, blinded by the fear of long setting times after a protracted completion process robbed us of two months on our construction programme. We now have time to review all our choices and learn for future projects.

1. Cost Comparison

Cement screed is the cheaper option, with an average cost of £15–£16 per square metre. For a 100m² project, this results in a total material cost of around £1,550.

Limecrete, by contrast, is more expensive, typically costing between 1.5 to 2 times more than cement screed. This means the total material cost rises to £2,325–£3,100 for the same 100m² area.

While limecrete does come at a premium, its benefits extend beyond cost alone. To determine whether the extra expense is justified, we must examine its environmental impact.

2. Carbon Impact Comparison

The key reason to consider limecrete over cement screed is its significantly lower embodied carbon. Cement-based screed has an estimated embodied carbon of 100 kg CO₂e per tonne, meaning a typical 100m² floor using 17.6 tonnes of cement screed will produce around 1,760 kg of CO₂ emissions.

Limecrete, on the other hand, has an embodied carbon of just 13.58 kg CO₂e per tonne, meaning a 14.4-tonne application would generate only 195.5 kg of CO₂ emissions.

The difference is stark: switching to limecrete reduces the project’s carbon footprint by over 1,500 kg of CO₂e, an almost 90% reduction in emissions from screed alone.

Carbon Offsetting vs. Low-Carbon Materials

When discussing embodied carbon, a common counterargument is that emissions can be offset rather than prevented. But what does this actually mean?

Carbon offsetting is a method of compensating for emissions by funding projects that reduce or absorb an equivalent amount of CO₂ elsewhere. These might include reforestation schemes, renewable energy projects, or carbon capture technologies.

Offsetting has become popular because it allows companies and individuals to “neutralise” their emissions without having to make substantial changes to their materials or processes. However, there are two major concerns with this approach:

        1.      Uncertainty in Carbon Offsets – Not all offset projects deliver the promised reductions. Some forests planted as carbon sinks are later destroyed by fire or logging, and some renewable energy projects would have happened anyway without the offset funding. This means that while the offset exists on paper, it does not always represent an actual reduction in atmospheric CO₂.

        2.      Timing of Emissions – Embodied carbon is released immediately, whereas offsets often take years or even decades to absorb the equivalent amount of CO₂. A tree planted today will take 40 years to capture the carbon emitted by cement production today. Meanwhile, climate change continues to accelerate.

If we compare the cost of using limecrete to the cost of offsetting, the numbers are revealed.

     •           The extra cost of limecrete is approximately £1 per kilogram of CO₂ saved.

     •           The cost of voluntary carbon offsets varies but typically ranges from £4 to £30 per tonne of CO₂e (or £0.004 to £0.03 per kilogram).

     •           At these prices, offsetting the 1,760 kg CO₂e emissions from cement screed would cost only £7–£52—far less than the additional £775–£1,550 required to use limecrete.

At first glance, this suggests that offsetting is far more economical than switching materials. However, given the growing scrutiny of offsetting schemes and the fact that offset prices are expected to rise dramatically as climate policies tighten, the long-term viability of this strategy is questionable.

More importantly, preventing emissions is always preferable to compensating for them later. Once carbon is released into the atmosphere, it contributes to climate change immediately. Using low-carbon materials like limecrete directly reduces emissions at the source, rather than relying on uncertain future offsetting mechanisms.

Is Limecrete Worth the Extra Cost?

Cement screed remains the cheaper option for projects with tight budget constraints. However, for those committed to reducing embodied carbon in a meaningful and verifiable way, limecrete offers a proven, immediate, and measurable reduction in emissions.

Additionally, limecrete provides other practical advantages beyond carbon reduction. It is more breathable, reducing the risk of trapped moisture and improving indoor air quality. It is also more flexible than cement, making it less prone to cracking over time. These properties may extend a building’s lifespan in specific contexts, further contributing to sustainability.

Ultimately, the choice between cement screed and limecrete comes down to priorities. If reducing carbon emissions in construction is a serious goal, then switching to limecrete is a real and effective step forward—even if it comes at a higher initial cost.

Final Thoughts

The discussion of sustainability in construction often focuses on high-tech solutions, but sometimes, the best answer is simply using better materials. Swapping cement screed for limecrete is a small change that drastically reduces embodied carbon—something that is not always true for other sustainability strategies.

Choosing materials with lower embodied carbon is one of the most reliable, transparent, and effective ways forward for those looking to make a genuine impact in sustainable construction.

Accelerating Action: A Holistic Approach to Net Zero and Sustainability

 

At the recent seminar at Sheppard Robson Architects, the panel—which included Sarah Allan (Head of Architecture, Ministry of Housing, Communities and Local Government), Helena Rivers (Net Zero Lead, AECOM), Lee Bennett (Partner, Sheppard Robson), and Joanna Yarrow (Chief Impact Officer, Human Nature)—discussed one of the most critical challenges facing architecture and urban planning today: what are the most urgent steps to improve our chances of achieving net zero while building the cities, neighbourhoods, and homes we need? The conversation highlighted several essential factors—public support, policy innovation, professional education, and the need for a holistic, large-scale approach—all of which must align to meet this ambitious target.

 

Inevitably, the discussion meandered through various topics for some time before, at least in my mind, converging on a seemingly shared view of the critical issues and the most urgent actions and reforms.

 

1. Start with a Vision

 

A key takeaway was that sustainability must operate on a scale much broader than individual buildings. It cannot be achieved one building at a time by well-intentioned designers; it must be a comprehensive vision permeating all aspects of life. Joanna Yarrow from Human Nature illustrated this point with her experience of living in Malmö, where sustainable transport and services are fully integrated into the city’s fabric. There, a mother can cycle to work on wide, safe cycle routes, drop her children at nursery—rain or shine—rely on a transit system designed around walking and cycline, down to the detail of a thoughtfully placed canopy.

 

I don’t know Malmö that well, but it did remind me of my time in nearby Copenhagen as a visiting PhD student. A German colleague of mine, who split her time between Copenhagen and Berlin, used to say, “When I come to Copenhagen, it’s like stepping into a five-star hotel!” Blue cycle path, actioned doors into bike stores, even footrests for cyclists and junctions. Of course, this modern-day Copenhagen is the product of decades of policies, from the post-war finger plan to Jan Gehl’s human-centred urbanism of the 1980s and ’90s—often involving unpopular measures. It’s an example that shows the importance of a vision.

 

As Sarah Allan rightly emphasised, having public support is crucial. Numbers alone—especially when they focus on restrictions—can alienate people rather than engage them. A proactive and positive vision like Malmo’s or Copenhagen’s can unite and meaningfully engage the public. And, of course, we’re not starting from scratch; this vision has informed so much planning and design over the last few decades, but it remains too fragmented and still competes with car culture. The government, as always, plays a critical role in setting the tone and shaping the policies around it.

 

2. Implementation at a Wider Scale

 

However, policies are not sufficient on their own. The education of professionals and civil servants who implement these policies is just as important. Planners, in particular, find themselves at the tricky crossroads of vision and metrics—ensuring the delivery of housing while assessing the sustainability of proposals beyond individual buildings. The conversation highlighted the difficulties in this area, with Helena Rivers from AECOM explaining how even agreeing on a definition of net zero across different scales remains a significant challenge. Here, the recent launch of the UK Net Zero Carbon Buildings Standard is a step forward.

 

3. Finally, the Buildings

 

And finally to construction, where Helena Rivers and Lee Bennett of Sheppard Robson made two points I passionately believe in. Firstly, the importance of prioritising retrofit without creating high carbon emissions—essentially avoiding scenarios where the carbon cost of retrofitting negates the benefits. (Our work on nomoregas.org is done in this spirit.) Secondly, they noted how some of the best designers and engineers are practically shut out of large-scale housing delivery, which is predominantly geared towards mass production. Inevitably, the discussion turned to the housing crisis and the target of delivering 350,000 homes per year. While this might initially seem to complicate things further, it doesn’t have to. The real issue is that we cannot deliver this number of houses at low density and with minimal sustainability targets while staying within our carbon limits. Instead, we must return to the vision of a sustainable lifestyle that works for everyone: higher densities, integrated public and cycle transport, and better buildings.

 

It seems we simply (though not easily) need to commit to a coherent project and work together to implement it as swiftly as possible.

1. Learning from Copenhagen

Copenhagen’s success as a model of sustainable urbanism is rooted in its Finger Plan, a transit-oriented development strategy introduced in 1947. The plan structured the city’s growth along five ‘fingers’ extending from the city centre, each connected by public transport routes and surrounded by green spaces. This design ensured that development focused on transit hubs, promoting efficient public transport use and limiting urban sprawl. It’s a classic example of transit-driven urbanism, where urban growth and transportation are planned hand-in-hand.

Fast forward to the 1980s and ’90s, and Jan Gehl’s work built upon this foundation, shifting focus to human-centred urbanism. Gehl, a Danish architect and urban designer, advocated for reclaiming streets for pedestrians and cyclists. His research highlighted the importance of public spaces prioritising people over cars, and his interventions transformed Copenhagen into one of the most bike-friendly cities in the world. The city’s blue cycle lanes, car-free streets, and thoughtful street furniture—like footrests for cyclists at intersections—are a direct result of Gehl’s approach. His work demonstrated how strategic planning and a commitment to liveability can create a thriving, sustainable urban environment.

AECB’s Carbon Lite Standard

In our ongoing effort to tackle climate change, the architecture and urbanism community always looks for practical ways to reduce carbon emissions. The Association for Environment Conscious Building (AECB) has developed some fascinating insights through its CarbonLite Retrofit (CLR) standards. They’ve found that these standards, which focus on cost-effective and realistic interventions, can achieve better carbon reductions than even the much-lauded Passivhaus standards. This is a major step forward for sustainability.

The CarbonLite Retrofit Approach: A New Benchmark for Sustainability

The CarbonLite Retrofit (CLR) standards offer a practical framework for significantly reducing energy use in existing buildings. The AECB’s CLR approach emphasises improving the building’s fabric with affordable measures that ensure substantial energy savings and improved thermal comfort. This down-to-earth approach is scalable and accessible, making it suitable for a wide range of buildings and budgets.

The key moves of for a Carbon Lite approach are very similar to what we advise on our www.nomoregas.org

1. An electric energy engine is the most important step towards reducing carbon emissions. Pragmatic and effective actions to reach a degree of insulation that allows the installation of a heat pump are the first considerations. Where heat pumps are impractical, other viable solutions are available at www.nomoregas.org 2. Insulation Requirements: For Step 1 retrofits, recommended measures include cavity wall insulation, 300-400mm loft insulation, and at least double-glazed windows. These ensure that the running costs of heat pumps remain manageable. 3. Ventilation: Installing efficient ventilation systems to maintain indoor air quality while minimising energy use. Proper ventilation prevents moisture build-up and ensures a healthy indoor environment. 4. Step-by-Step Approach: The CLR standards allow for a step-by-step approach to retrofitting, where the process can be done in stages. Step 1 is the minimum permissible step, offering a low-carbon interim measure that can be built upon with deeper fabric retrofits in the future.

Retrofit project in Westminster Mansions, London.

In the top left corner, cables ready to connect the infrared heating (NO gas boilers?). The external wall is ready to breathable insulation and plaster to improve the thermal performance without compromising the building’s thermal and moisture balance.

Key Findings from the Green Register Seminar

During a seminar organised by the Green Register on 12th March 2024, Tim Martel, AECB Standards & Certification Programme Manager, presented findings on the CarbonLite Retrofit standards. The seminar highlighted that the CLR standards produce fewer carbon dioxide emissions than the Passivhaus standard, traditionally seen as the gold standard in energy efficiency. This underscores the effectiveness of cost-effective, pragmatic measures in reducing carbon emissions.

The seminar presented a graph illustrating how the CLR approach, which includes affordable interventions on the building fabric combined with replacing the heat engine with a heat pump, resulted in lower carbon dioxide emissions than all other retrofitting types, including Passivhaus (EnerPHit) standards.

Detailed Insights from the Seminar

Visualising the Impact: The Carbon Emissions Graph

The AECB’s findings were illustrated through a graph showing cumulative CO2e (operational + embodied) emissions over 60 years for a semi-detached house. The graph compared various retrofitting approaches:

• 194 tonnes CO2e for a gas boiler.

• 99 tonnes CO2e for CarbonLite Full Retrofit without ASHP.

• 76 tonnes CO2e for EnerPHit without ASHP.

• Significantly lower emissions for CarbonLite Step 1 Retrofit with ASHP, showcasing it as the least carbon-intensive intervention.

The Benefits of CarbonLite Retrofit

The benefits of adopting the CarbonLite Retrofit standards are manifold:

1. Cost-Effectiveness: The CLR approach focuses on affordable interventions that are accessible to a wide range of building owners, making it a practical solution for achieving significant energy savings without requiring substantial financial investment.

2. Scalability: The pragmatic nature of the CLR standards makes them scalable, allowing for widespread adoption across various building types and sizes, crucial for achieving large-scale carbon reductions.

3. Health and Comfort: By improving insulation, airtightness, and ventilation, the CLR approach enhances overall health and comfort in buildings, benefiting occupants and contributing to the building’s longevity and durability.

4. Environmental Impact: The integration of renewable energy sources and replacing gas boilers with heat pumps significantly reduces the carbon footprint of buildings, a critical step towards achieving net-zero emissions.

Case Studies and Practical Applications

The AECB has documented several case studies illustrating the effectiveness of the CarbonLite Retrofit standards in real-world applications. These case studies provide valuable insights into the practical implementation of the CLR approach and demonstrate the tangible benefits of adopting these standards.

For example, a retrofit project in Bristol utilised the CLR standards to transform a Victorian terrace house. By upgrading insulation, improving airtightness, and installing a heat pump, the project achieved significant energy savings and improved thermal comfort for the occupants. Similarly, a community housing project in Manchester showcased how the CLR standards could be applied to achieve substantial carbon reductions in a cost-effective manner.

Conclusion: A Pragmatic Path to Sustainability

The AECB’s CarbonLite Retrofit standards offer a pragmatic and cost-effective path to achieving significant carbon reductions in existing buildings. By focusing on affordable measures and integrating renewable energy sources, the CLR approach provides a scalable solution that can be widely adopted to combat climate change. As we continue to strive for a sustainable future, the CarbonLite Retrofit standards represent a vital step forward in our collective efforts to reduce carbon emissions and improve the resilience of our built environment.

References and Sources

1. Association for Environment Conscious Building (AECB). (2024). CarbonLite Retrofit Standards. Retrieved from AECB Website. 2. Green Register. (2024). Seminar on CarbonLite Retrofit Standards. Retrieved from Green Register Events.

3. Martel, T. (2024). CarbonLite Retrofit: Achieving Net Zero in Existing Buildings. Presentation at the Green Register Seminar. 4. Passivhaus Trust. (2024). EnerPHit Standard. Retrieved from Passivhaus Trust.

Gas boilers are responsible for several types of pollution: carbon monoxide is particularly dangerous indoors and can kill or seriously poison inhabitants[1]. A high concentration of gas boilers seriously impacts air quality, particularly in cities. For example, in London in 2010, gas boilers contributed 21% of the NO2 pollution, second after transportation, which accounted for about 50%[2]. In these areas, replacing gas boilers with electric alternatives brings more benefits than in others by reducing diseases and mortality in children and adults.

The map shows NO2 concentrations in the UK, where www.nomoregas.org can be more useful[3].

By overlapping technical/architectural knowledge and urban and geographic information, we could now design more granular policies to capture maximum advantages. For example, heat batteries and other electric alternatives to gas boilers could be incentivised in dense urban areas.

At the same time, when discussing curtailment, we noted how installing thousands of heat batteries in some areas of the North and Scotland would save the government and everyone energy and money.

The combination of these two geographies forms a National (albeit still partial) map of areas where transitioning away from gas should be favoured or incentivised.

[1] According to the government, every year, “4,000 people go to A&E, 200 people are hospitalised, and there are around 50 deaths in England and Wales”. https://www.gov.uk/government/news/carbon-monoxide-poisoning-sends-4-000-people-to-a-e-each-year
[2] I suspect now the proportion will be a lot higher, thanks to the reduced pollution from transport (The Mayor of London has invested a lot into this campaign and policy).
[3] To see the NO2 maps visit https://naei.beis.gov.uk/mapping/mapping_2020/6_large.png

We have known for decades now that the future energy mix will be based on renewables, and the key to a sustainable future is the electric grid. Buckminster Fuller proposed a global electric grid in the 1930s and worked on the project for several decades. Since the early 2000s, OMA – Office for Metropolitan Architecture – has been developing scenarios for the European electric grid, where the Mediterranean countries supply solar energy and the Northern countries wind. The latest rendition of this idea is Eneuropa, again by AMO (the research arm of OMA), with McKinsey, Imperial College London, energy consultancy KEMA and analyst Oxford Economics. On the right is a portion of the map, where the UK spans between the Isles of Wind and the Tidal States. The most important and costly investment to implement this plan is a new long-range and powerful electric grid.

‘The power sector requires the most aggressive change,’ says AMO project director Laura Baird. Roadmap 2050 proposes a European supergrid where UK winds and tides, Mediterranean sunshine and central European forests work together to reduce Europe’s reliance on fossil fuels.

The main idea is that large-scale, efficient grids will reduce the intermittency issues tied to renewables (the sun is always shining somewhere). We could and should make the same reasoning in the UK. To contribute and take advantage of the European grid, we must build our own and maximise the richness of our renewable production.

In fact, large amounts of renewable energy are wasted yearly because of how the grid is built. This map illustrates the break between the Northern and Southern grids. Most renewable energy providers are in Scotland and Northern England, which does not consume all of it. On particularly windy days, energy from Scotland and the North could supply almost all the power we need. However, delivering this power where needed is impossible because of the lack of transmission lines between the energy-productive North and the energy-hungry South. So when the output is too high, the energy grid needs to pay wind farm owners to stop the turbines to avoid overloading the grid.

According to this perfect article by Archy de Bercker, curtailment costs us about 1 Billion(!) in fees and wasted energy. The government is planning new transmission lines and faces much resistance and NIMBY-ism. Therefore the largest transmission lines are planned on the sea bed and will take years to build. While building the transmission lines, the Scottish renewable energy output will increase further, making even the new lines obsolete.

Simply put: we can’t lay cables fast enough to solve this problem.

According to Archy de Bercker, the ideal solution would be a more diffused grid: with several connection points. Again, this would require overcoming a lot of resistance. Local and national governments need all the possible support to design the new lines properly by involving and informing the citizens about the knowledge on upgrading the grid. But there are also other options: Other means of making the most of otherwise wasted energy would be to deploy battery storage on the energy-abundant side of the divide. Batteries can be deployed at large or small scale. Heat batteries can always draw electricity to recharge, especially at night when there is often too much output (and energy is cheaper). These products are designed precisely to take advantage of the low-cost energy to provide:

I. a service to the grid that needs a way of balancing before getting overloaded;

II. A way to avoid wasting energy through curtailment;

III. Lower bills for its owners

For these reasons, we have included them among our recommended solutions to electrify our homes and replace gas boilers. Instead of wasting one billion pounds a year, we could invest in incentivising the installation of heat energy batteries to replace boilers, especially in areas where power goes wasted: Scotland and Northern England.

To find the best for you on a free-pro-bono website built by environmental activists and architects, check out www.nomoregas.org.

Read more about this:

https://archy.deberker.com/the-uk-is-wasting-a-lot-of-wind-power

https://www.theguardian.com/artanddesign/gallery/2010/may/07/architecture-rem-koolhaas

Our first peace and climate campaign.

​

During our recent reflection on ecological design and architects/urbanists’ role in society, we concluded that we should expand our agency by getting involved in issues we care about.

We also anticipated we would start with natural gas. Why gas? We care about the climate crisis and we care about peace. For several weeks now, we have been glued to the news cycle, hoping that the war would end. We have decided to at least try to do something: but what should we do?

Fossil fuels are at the intersection between climate crisis and geo-politics, therefore contributing to the transition to renewable energy will serve two purposes. After long reflection we decided to adopt a literal approach and accelerate the phasing out of natural gas from UK homes [1]. Gas boilers and hobs, gas meters and bills, risks related to carbon monoxide, gas safe certificates: the whole thing. If we manage to help one thousand homes transition away from gas, we will save thousands of tons of CO2 and at least symbolically work against the aggressor in Europe.

How?

We think the best way of getting rid of gas in homes is to provide unbiased, precise information on viable alternatives, especially for cases that are usually overlooked. A balanced investigation will not only help people who are already interested but could also help shape government policy towards embracing new opportunities. We call our research and campaign nomoregas (#nomoregas).

Now that we have a goal, we need a plan. First, we want to narrow the subject by examining the current energy technology landscape. We are looking for cases with the potential to transition that have been ignored so far for lack of technological solutions or creativity. Second, we will create an alliance with think tanks, experts and manufacturers to tap into the best knowledge and ensure accurate analysis. Third, we will test transition scenarios by checking costs and performances for the most promising technologies compared to business as usual. Finally, we will collect the data and produce a guide [2].

​

I. Weak points

Typically, the financial case for getting rid of gas boilers is more compelling in energy efficient buildings. For example, new-build homes will have to be gas-free from 2025. Those cases are so straightforward that we will not investigate further. The case is more difficult for existing buildings, which are complex, expensive and sometimes risky to insulate beyond a certain degree. The 7 million solid wall homes (any home built before the 1920’s) in the UK are very leaky on average [3], and there is little incentive to drive the almost revolutionary scale of retrofitting that would be necessary to significantly upgrade these buildings. Without incentives, retrofit projects are very expensive upfront and make financial sense only in the long run [4]. Pair that with a pretty much global tradition of subsidising fossil fuels, which make the advantages of retrofitting even less visible, and the outlook is grim. In conclusion, retrofitting a (solid wall) home is expensive, and existing homes are also where most of the poorest people live.

​

Of all the existing homes, we decided to focus on the single-family homes because they are usually overlooked compared social housing and higher-yield interventions. It’s quite clear that, unless there is a miraculous shift in policy, existing, uninsulated homes will be the last to transition to electric energy engines – as in fact it is confirmed by the current policy, which expects to phase out gas boilers in existing homes from 2035 [5]. So, the aim of the study will be to find solutions to bring forward this date with only minimal intervention on the fabric (while we lobby for more incentives, of course). In other words, our working base case will be an existing home where a boiler needs replacing. The only incentive we will rely on is the broken gas boiler.

2. Finding case studies

We are now looking for easily comparable case studies to test new solutions and assumptions in the boiler needs replacing scenario. After extensive research, we selected a report compiled by The Carbon Trust for the GLA in 2020 (The Carbon Trust, 2020) that looks precisely at the financial and environmental implications of replacing a gas boiler with electric alternatives. The report is extremely well thought and thorough, but focuses almost exclusively on heat pumps, because it was published in 2020, and its authors could not see it in the future. Therefore, it does not factor in the increased costs of gas, the moral imperative some people feel, and all the new solutions that have come to the market in the UK and Europe in the last two years.

Hence, the study finds only heat pumps as viable substitutes for boilers. Aside from this, the document is a little masterpiece in proactivity, thoroughness and clear communication. The study analyses fifteen London properties of varying sizes and energy insulation, from the tiny ground council flat to the large detached Victorian house. For each property, the report analyses the financial and environmental implications of replacing the gas boiler with a heat pump. Two reasons why it’s a masterpiece (in my view). First, the approach is very pragmatic: it avoids as much as possible factoring inexpensive fabric upgrades and focuses exclusively on the heat source. This is contrary to environmental and retrofit orthodoxy: our credo is always fabric first; or the cheapest energy is the one you don’t need in the first place (I could go on). But in this case, we are focusing on the heat source only because the situation we want to tackle is a boiler that needs replacing. We cannot realistically hope that everyone replacing their boiler will have £20-50k available to do some essential retrofitting, and we don’t want to wait for the government.

​

The second reason why we appreciate the report is the clarity of communication. The Carbon Trust does a great job at boiling down the comparisons to very few, easily comparable graphs, and to one final parameter: the cost per tonne or removed CO2. This parameter tells us not only whether the heat pump alternative is viable for the single user, but also for society at large. In some cases, the financial case seems not to be there: at a cost of £700 per ton of CO2, for example, it may be better to invest in a wind farm than to replace the boiler. At the same cost, even the government should probably avoid incentivising change while focusing on other solutions. Finally, the same parameter is handy because it shows exactly where we should focus our attention: cases where the cost per ton of CO2 reduction exceeds £300 need our help.

​

Our aim now is even clearer: to find design and technological solutions to expand the pool of cases that can viably transition away from gas when their boiler reaches end of life. The report’s conclusions confirm our intuition on single-family homes, which do not figure in the list of viable building types (page 5 of the main document and page 31 of the Options Appraisal):

The up-front cost of heat pumps is higher than traditional alternatives and many building types will require additional up-front financial support. However, the lifetime financial case for heat pump retrofit is already strong in some building types, such as electrically heated buildings, buildings with a high cooling demand and buildings that already require major renovations. These building types should be prioritised for heat pump retrofit.

​

[…]

There is already a compelling financial case for deploying heat pumps in some London building types.

· Homes, blocks of flats and non-domestic buildings heated by electricity.

· Buildings with a high demand for cooling such as large office buildings.

​

• Blocks of flats where upgrades are required to the heating systems and heat distribution systems in any case.

​

To better understand these conclusions we have plotted in the diagram below, showing all the cases that didn’t make the list and two that have.

The coloured cells highlight the cost per ton of CO2 removed by switching away from gas boilers.

Reds are higher costs, green are lower costs.

Trends.
The coloured column reflects the cost of switching from a gas boiler to heat pump, divided by the tons of CO2 reduced. This reflects the absolute cost to the world at large, not yet a business case, but it’s very useful to understand how to tailor the new investigation. Roughly speaking, the size of the property increases from top to bottom, from flat to block of flats. There seems to be a direct relationship between size and viability. Case no.5 is the only exception because it is already heated with an electric boiler, which (in 2020) is or was very expensive to run. By replacing the inefficient boiler with a very efficient heat pump the savings are so high to offset the extra cost for the heat pump in no time. In all other cases, the comparison is with a gas boiler and the relatively inexpensive gas prices in 2020.
The only other factor to account for is the current EPC rating of each property. But we can say that within a relatively wide range of EPC ratings, from B to E, the size of the property holds the strongest correlation. This is because heat pumps are expensive and need at least a 150 square metres playing field to make their efficiency count.

It is clear that in the current energy market, smaller properties that do not require extensive refurbishment do not benefit from heat pumps. We need alternatives to both gas boilers and heat pumps, and this is what we are going to focus on first.

​
Actions
Finally, we have a plan of action.
First of all, we will ask The Carbon Trust to update the figures considering the latest gas prices and the recently introduced £5000 tax break from the government. Secondly, we will suggest to analyse a 20-year life span which is what we expect of an energy engine today and therefore use 2040 as the real ultimate deadline. (This will make comparisons easier – the 2030 and 2050 dates are more aligned to the carbon targets but less to the matter at hand. The 2030 deadline is also biased in favour of gas boiler which have a shorter lifespan compared to heat pumps (at least according to the report); 2050 is in my opinion too far a horizon for a single-family home; no one makes investments with 30 years return!)
Third, we will offer to help with alternative test designs and mechanical solutions.
Finally, we will reach out to consultants, experts and manufacturers to compile a list of all possible alternatives and combinations of alternatives to gas boilers in existing single-family homes.

Call to action
Collaborating with the right people and organisations will be crucial to delivering an effective tool. So if you know anyone we should speak to in the energy, insulation, government and non-government policy experts, and consultants, please contact us or simply share this post.


Update June 21st, 2022

• We have been introduced to three world-experts on the topic of residential energy. We have discussed with one, who has warned us against the risk of transitioning too quickly to electricity, given its price.
• Carbon trust does not have the resources at the moment to either discuss or update their report’s data.
• Things are more complicated than we thought..

​
[1] The energy transition from fossil fuels should transform all sectors, but we think that agriculture and existing homes will be the trickiest, followed by the energy generation. Agriculture is outside our field of expertise (for now..), so we will look into existing homes.

[2] (As you might imagine, the process is messier and more iterative: steps 1-4 happen simultaneously and are repeated several times, slowly learning and adjusting.)

[3] In the late 90’s and early 2000’s several incentives allowed to upgrade millions of homes, but since 2013 a shift in policy has caused a complete stall in retrofit projects. (TBI has a good report on this aspect, here). The lack of incentives continues to date. The regulations on energy efficiency have been greatly scaled down.

[4] And the financial incentives are often upside down: for example, today new-build homes are VAT exempt, while expenses tied to retrofitting an existing home – no matter how well designed for efficiency- pay 20%! The only discount is on the insulation material itself, but there are so many exceptions to make it almost useless.

[5] (https://www.energylivenews.com/2021/10/18/boris-johnson-confirms-ban-on-all-new-gas-boilers-by-2035/).

The not-for-too-long problem
Historically, directly supplied natural gas has been a lot cheaper than electricity: this is why gas boilers are still the standard energy engine in most homes. And this is why simply switching to electric boilers was considered wasteful. Instead we need something as miraculous as a heat pump or as effective and expensive as insulation to make electricity competitive.
​
But one of the founding principles of our campaign is that the price of gas is skyrocketing while renewables are getting cheaper every second. We thought that the cheaper renewables combined with the much more expensive gas price due to the war in Ukraine would level the playing field. When electricity and gas reach a similar price (hopefully because electricity becomes cheaper), several electrical products that today are considered too wasteful or expensive suddenly become competitive.
​
So we were amazed to see that electricity prices had increased together with gas prices and more, compared to when the Carbon Trust’s report was drafted!

The report stated:
For domestic customers, we assumed a standard gas tariff of £0.032 per kWh and a standard electricity tariff of £0.152 per kWh, in line with the Treasury Green Book Central Domestic rates. I.e. our electricity standard tariff is assumed to be 4.75 times the cost of gas per kWh

The prices have more than doubled, with a gas kWh now costing about £0.075 and electricity increasing from £0.152 kWh to 0.29 kWh. The result is an even more dramatic difference between the two sources[1]

Gas and electricity prices are in effect tied in a coupling mechanism, by which the price of gas determines the cost of electricity, also the electricity produced by renewables! The reason for the coupling made sense some time ago, but the mechanism is now causing distortions and undermining the growth of renewables (as well as part of the foundations of our research).
Europe has a similar energy pricing system, but also a more diverse legal landscape. For example, Being less integrated into the continental energy network and much more reliant on renewables,

The UK is in a similar condition: it is not integrated into the European energy networks, doesn’t import gas from Russia, and has a solid renewable supply. Hence, we think we should expect the gap between electricity and gas prices to drop and eventually disappear in the coming few years.
The current price increases have put so many people under fuel stress that the government is considering reforming the market as soon as this year (2022); other institutionas are pushing for more complex and localised models for energy pricing. If we take advantage of the renewable energy we generate, perhaps by adjusting to a less consistent supply, the #nomoregas campaign will have a much easier life.
So this is something to hope for and perhaps lobby for: a reform of the energy market that reduces energy bills by decoupling gas and electricity prices while maintaining incentives for installing and consuming renewables.

Of course, we cannot rely on government legislation to start a revolution . But we can assume that at some point, the cost of grid-scale renewables will be so low and their use so predominant that electricity will cost less than gas. In fact, as of last year, the cost of installing renewables and energy storage combined has become way less than building new gas plants. TransitionZero, among our heroes, have mapped the cost tracked and all the prices in hypnotising animated graphs (the screenshot below does no justice to their beauty in movement).

Finally, using data from the electric grid’s forecast, the Carbon Trust’s report calculates that by 2025 direct electric heating will be more carbon-efficient than gas boilers, thanks to the accelerating decarbonisation of the grid. We can only hope that TransitionZero’s data and the current energy crisis will accelerate the trends described in this post. For the moment, we are satisfied with the conclusion that within three-four years, direct electricity will be more carbon-efficient and may be cheaper than natural gas. Does this mean that direct electricity energy engines will be competitive with gas in the near future?

Carbon intensity of gas boilers [,direct heating,] and heat pumps at different efficiencies: 2010-2050 (The Carbon Trust, 2020)

[1] Electricity prices still follow closely the fluctuations of gas prices. https://www.economicsobservatory.com/why-are-uk-energy-prices-rising

[2] https://www.sciencefocus.com/news/why-cant-renewable-energy-sources-keep-uk-energy-prices-down

For some time, we asked ourselves about our role in society as architects and educators. We decided that our mission should be to expand the agency of ecological thinking and design. We would do so by becoming better professionals, producing knowledge through our work and research, and becoming activists. The question of the agency of architects and ecological designers had partially sprung from the news of war in Europe and a frustrating feeling of impotence. Putting pen to paper to express this frustration was fruitful: it helped us decide to research the energy crisis and the war from an ecological designer’s perspective.

#nomoregas is at the crux of research and activism.

Why gas boilers? We knew that gas boilers are friends of several invasive regimes; then we discovered that they are also the next biggest obstacle to achieving net zero (combined, they are by far the biggest CO2 emitters in the UK) and among the worst sources of urban pollution. The difficulty of getting rid of gas boilers is the lack of viable alternatives. Heat pumps, albeit a magnificent work of engineering and a crucial piece of the net zero strategies, do not work for millions of flats and small houses or people with fewer means.

#nomoregas is born from our overlapping environmental and social justice passions.

We decided to investigate all the alternatives to gas boilers for heating and hot water, both in the case of properties needing refurbishment (generally easier) and when only the boiler needed replacing. We investigated, interviewed, and sometimes tested several products. We then connected products, or combinations of products, with their best application. Finally, we built an easy-to-use selector so that homeowners and designers can quickly identify the right solution for them or their project: whether it’s a flat or a house, 50 or 100 square metres and so on. Although not all are perfect, and some are expensive, we succeeded in identifying feasible solutions for every case.

#nomoregas is an information platform for people and designers who wish to find alternatives to gas boilers and a guide to the future electrified society.

The beta version of the website is up and running.

We now want to work with institutions and thought leaders in the design and energy sectors to expand the website’s visibility and impact; by involving the right people, we hope to bring this particular topic to the centre of the energy transition conversation.

– City authorities may be interested in the impact on air quality and may want to help bring this topic to the attention of the central and regional governments.

– Policy-makers could recognise the opportunity of helping growing innovative companies that are tackling the energy transition’s most difficult problems.

– Designers and designer bodies can celebrate the expansion of our profession’s agency and foster the development of the website as a tool for design by providing feedback, advice, exposure and funding.

– Researchers can collaborate with and use the platform to inform more people and affect the public debate.

#nomoregas competition, call for papers, and exhibition

Our main goal is to slow climate change and reduce the use of gas, but as an architecture practice, we can’t refrain from imagining the impact of the electrified home on the physical world. In the future we want to launch a call for papers and a design competition to discuss the future of the electric city and the electric home.

– What will the heat batteries of the future look like?

– What are we going to do with all those useless flues? How will we fill millions of holes into the building fabrics where flues used to be?

– What is it like to be traversed by infrared light?

– Heat battery architectural integrations:

o The pediment

o The pad foundation

o The front pilaster

o ….

– Small changes to homes that will affect our everyday lives and urban landscapes.

Stay tuned for more.

(Above, 1925 Figini e Pollini La casa elettrica. Below, 1956, Smithsons’ Home of the Future)

One year since the beginning of the war, here is our third post of the #nomoregas campaign, which aims to accelerate the transition away from gas boilers (posts 1 & 2 are here). In this post, we will analyse lesser-known alternatives to the gas boiler. To recap, we want to find solutions for the cases where installing a heat pump is not feasible or financially viable: typically flats and medium-to-small houses that will not be refurbished in the near future. The fourth post will introduce a new website dedicated to designers and homeowners who want to remove gas from their properties, so stay tuned!

Gas in the UK homes: a tough enemy..

There are 26 million gas boilers in the UK, producing more than double the CO2 of all gas powered stations in the country. [1]

{Each boiler produces} “3.54 tonnes of carbon dioxide equivalent a year, amounting to over 92 millions tonnes annually. This is over double the 41 million tonnes of emissions created by the UK’s 48 gas-fired power plants.” The plan to decarbonise relies heavily on replacing gas boilers with heat pumps, but we are installing nowhere near as many as we need. The Economist noted recently: “Of Britain’s 24.7m homes, 74% are exclusively heated by gas [2]. Home heating accounts for 14% of Britain’s total carbon emissions. The 43,000 heat-pump sales in 2021, the latest year for which full figures are available, falls far short of the rate of 600,000 per year by 2028 which the government has targeted.” And the cause might be just intrinsic to our housing stock [3]: Part of the problem is the history of Britain’s housing stock The coal burnt in Victorian-era fireplaces was replaced by “town gas”, a potentially lethal combination of carbon monoxide and hydrogen. As a result the priority was usually to build new homes that could get pollutants out rather than keep heat in. Draughts were a feature, not a bug. Heating systems were in turn designed to run hot to compensate for such poor insulation. [4]

Heat pumps have other downsides that don’t make them viable in several situations. The #nomoregas research and campaign aim at easing the transition away from gas by identifying financially and practically viable alternatives to gas boilers and heat pumps.

Some alternatives to gas boilers, explained

As we can see, heat pumps are the most popular alternative to gas boilers, but not every property can be easily converted. Heat pumps require external units and may require interventions on the building fabric or the plumbing system. They are also quite expensive; even with government incentives, a fully installed system will cost in the region of £9k.

So for flats, heat pumps are often out of the question: they are too expensive, and there is no space for external units. The main barriers for small houses and garden flats are installation and adaptation costs.

In our second #nomoregas post, we introduced the concept of grid balance and how we could use the varying price of electricity to make alternative products viable. In brief: while it is difficult to preview the future of energy, we can make some assumptions based on current trends and progress in recent years. The UK is in the privileged position to de-carbonise the power grid, thanks to the abundant wind, and the government plans to do this by 2035 (whether it achieves 90% or 100% it’s not relevant to us, what this means is that electricity will become cheaper in the coming years. Cheaper electricity means that the transition away from gas boilers will not cause energy poverty; quite the opposite. It is hard to understand why this transition is not translating into homes. As renewable energy technologies become more widespread and mature, the electricity cost will decrease, making new alternatives to gas boilers accessible to everyone. Even in this positive outlook, renewables’ intermittency causes imbalances on the grid, which must now deal with peaks and troughs in demand and production. The result is there are a few peak hours when the cost of electricity is extremely high and some hours at night when electricity costs are very low and sometimes negative!

A new range of products that works on a different principle has emerged in the last few years; we will call them heat batteries. Instead of producing renewable energy, heat batteries take advantage of the difference in electricity cost between day and night by charging with heat during the night and using the stored heat when needed. The result is not only cheaper electric heating and hot water, but also a big hand stabilising the grid (by drawing when there is peak offer and reducing peak demand). In other words, heat batteries are exactly what we were waiting for.

Here are the most promising product ranges that take advantage of this system.

I. Heat engines that can replace gas boilers.

II. Hot water cylinders have been around for a long time. These can be easily transformed into heat batteries, when combined with smart sensors and planning software.

Further down, we will explore systems that can integrate with smart heat batteries to expand their viability.

I. Heat engines: gas boiler replacements

ZEB by Tepeo:

The Zero Emission Boiler (ZEB) manufactured in the UK by Tepeo is the star of our investigation. It is a heat battery with a ceramic core that can be heated up to 800 C and maintains its temperature for several hours. It is a large, heavy box, the size of a washing machine, and it weighs 350kg, but once the access and weight hurdle is solved, it can be installed anywhere quite easily by most plumbers, and it doesn’t need a flue.

Zeb has an internet connection, drawings real-time information about the grid and live weather data and combines the information with the historical use of the house to take advantage of the best electricity prices throughout the day and night. Typically, it will draw most of the energy it needs during the night when electricity is cheaper and less carbon-intensive and only top up when necessary during the day.

PROS: The ZEB is compatible with a normal boiler installation. If you are refurbishing, you can run your existing gas boiler for the last couple of years to save money (windows, floor and loft insulation), but remember to reinforce the floor and verify all other compatibility aspects (see below our setup instructions).

What do you need to check:

• Weight: the ZEB weighs 350kgs, so it can’t just sit anywhere. Its ideal location is on the ground floor, or if you are refurbishing the property, you can reinforce the floor where you plan on installing the ZEB for peace of mind.
• Access: the weight and size also create a few problems for the installation. Very tight stairs could prove impossible to conquer.
• Cost: The ZEB is not the cheapest at £6000, including VAT. It will pay itself in the long run, but it is still an investment. The government doesn’t consider energy batteries worthy of incentives; we disagree.

• Maximum power: at a maximum of 12000 kWh per year, the ZEB is suitable for properties up to 120-130 square metres (unless super insulated).
• Electric power load: the ZEB draws 40 amps. The typical home fuse is 70Amp, giving ample load for other items. Nonetheless, if you have a lot of other electric loads you should consider upgrading the fuse to 100 Amp.
• You’ll need to switch your energy provider to one that gives discounts at night. Octopus energy, for example.

II. Smart hot water cylinders: the ideal support for alternative heat engines

I.a. Mixergy is a simple hot water cylinder with a couple of twists.

Firstly, it heats the water from the top. Hot water stays on top, so it doesn’t mix with the cold water at the bottom and stays consistently warm. This means that the heater can calibrate the hot water required and only heat that much. Second, it is smart: the tank learns your habits to be as efficient as possible. It will typically build up a reserve at night when electricity is cheapest and only reheat what you need (if you still need some) during the day.

Mixergy tank (Source: https://www.ecobubl.co.uk/)

Versus the traditional hot water heat battery:

Sunamp uses a phase change material. It is a heat battery in the sense that it stores heat, but it does not have the capacity or the software capabilities to take advantage of the flexible pricing. It will draw electricity when necessary. It has a capacity of to 12kWh, which typically means it can only provide hot water, but not heating.

Heat batteries and Sunamp (Source: Delta-EE)

Direct electric heating solutions

Unfortunately, heat and hot water batteries do not cover all our case studies. Each system has some limits, and almost every house is different. We propose to use direct electric backup systems to bridge the gaps and still avoid installing gas boilers. Direct electric heaters are less efficient than heat batteries discussed above, but if we design the systems properly, we only need them during the coldest days of the year. Here are two examples.

Infrared heating

Infra-red panels and fabrics. Infrared heating is different compared to the air heating we are used to. Radiators heat the air, and underfloor heating heats the floor, which heats the air; infrared heating is more akin to the winter pub heaters (without the light): you feel the heat on you, and the waves heat the objects around you. The outcome is potentially more efficient than ambient heating because it is less susceptible to loss from air movement (a draughty window, opening the entrance door, or just doors between different rooms).

The second advantage is the quick sense of comfort, which makes infrared particularly efficient in rooms used intermittently, like guest rooms, utility rooms and bedrooms. Infrared heating comes in two formats:

• Panels are usually large and white and are usually installed on the ceiling. These are perfect for installing when there are no refurbishment works in sight.
• A special mesh can be plastered into the ceiling and walls to become invisible. Of course, this is our favourite option when refurbishing.

Electric radiators

Our last resort solution. Electric radiators are the least efficient tool in our toolbox. Still, it has a role in the mix of gas-free solutions: to boost the heating system during the coldest days. Heating systems are designed to have enough power for the coldest days of the year. When we can’t afford the fully specified system, for cost, space or simply because there are no suitable products, we can provide backup with electric radiators.

• Their main advantage is flexibility and low installation cost: they only need a socket. They can be switched on and off at will.
• Their response is relatively quick.

Cons:

• Inefficient and tasking for the electric fuse: each radiator draws about 4Amps, so they cannot be a complete replacement for the heating system, nor an extensive solution. But four or five radiators can go a long way on cold days.

Direct electric radiators and infrared heating are a risky bet: their success depends on the price of electricity going down. From a carbon balance point of view, we risk drawing electricity at peak time, which may be more carbon-intensive than gas. As discussed, our take on this point is that the grid will be less and less carbon intensive, and the cost of electricity will drop in the coming years. Nevertheless, should the short-term consequences of using direct electric heating be a concern, electric batteries (e.g. the Tesla Powerwall) can help us take advantage of the lower price and carbon intensity of off-peak electricity that can be deployed on demand to the electric heaters.

Conclusions: what is the best solution?

Current trends in energy supply and new products are making the transition away from gas boilers viable for almost everyone. Combined, heat pumps, heat batteries and direct electric heating systems provide a mix of solutions to cover almost any case. Navigating the myriad of cases and products can be daunting, because there is no single answer. So we have decided to create a website that helps designers and homeowners choose the right alternative to gas for their case. The website is in beta version but will be online by the end of March.

Stay tuned!

[1] https://www.desmog.com/2021/09/29/uks-26-million-gas-boilers-produce-double-the-emissions-of-countrys-gas-power-plants-study-finds/

[2] https://www.economist.com/technology-quarterly/2018/11/29/in-the-rush-to-renewables-decarbonising-heating-has-been-overlooked

[3] https://www.economist.com/interactive/britain/2022/11/29/how-to-fix-30m-draughty-homes

[4] https://www.economist.com/britain/2023/02/06/the-heat-pump-challenge-in-britain