Athelhampton:
exploring energy transition in historic homes

On the 12^th November 2024, the stunning Athelhampton House set the stage for the second instalment of Moulding’s seminar series, Strategic Energy Decision Making in Historic Houses. Organised in collaboration with SPASE Architects, the event brought together a mix of expertise, enthusiasm, and innovative thinking to tackle the challenges of retrofitting historic properties for a sustainable future.

The seminar kicked off with a warm introduction from Tim Moulding, Managing Director of Moulding, who reflected on the success of the inaugural event and shared his vision for the series. Tim highlighted the importance of helping historic house owners navigate the complexities of energy transitions while preserving the architectural heritage we all hold dear.

The day was expertly chaired by Nick Jenkins, a passionate advocate for renewable energy, who hosted the previous seminar at Stockton House. At Stockton, Nick showcased his ground-source heat pump technologies, and he brought the same enthusiasm and insight to Athelhampton.

The panel featured a fantastic lineup of experts:

• Tim Moulding, host and owner of 8^th generation specialist residential building firm Moulding.
• Nick Jenkins, experienced property owner and renewable energy advocate.
• Stefan Pitman and Sarah Small of SPASE Architects, who have been instrumental in award-winning retrofitting projects.
• Mike Stephenson of H2Eco, a leader in renewable energy system design and installation.
• Bean Beanland, Chair of the Heat Pump Federation, who brought a national perspective to the discussion.

The audience was a carefully curated guest list of country house owners, creating a vibrant space to share experiences, ask questions, and learn from the experts.

A highlight of the day was the tour of Athelhampton House, where attendees saw the retrofit technologies in action. A particular focus was on the surprisingly quiet Air Source Heat Pumps, which were a key talking point from the first seminar. Many had questioned whether such systems could function discreetly in historic settings, and the demonstration confirmed their unobtrusive performance.

With practical insights, and opportunities to witness cutting-edge technologies at work, the day proved to be an inspiring and informative gathering.

If you weren’t able to join us, don’t worry – we’ve captured all the key highlights in this blog. Whether you’re a historic property owner, a sustainability enthusiast, or simply intrigued by the future of heritage conservation, this recap will bring you up to speed on an exciting day at Athelhampton House.

Athelhampton House: a blueprint for energy transition in historic estates

Athelhampton House, a Grade I listed manor in Dorset dating back to 1485, has undergone a groundbreaking energy transition. Guided by SPASE Architects and H2Eco, this ambitious retrofit merge heritage preservation with cutting-edge sustainability technologies. The multi-award winning project’s achievements – culminating in dramatically reduced carbon emissions and energy costs – have set a benchmark for retrofitting historic properties.

Project Origins and Goals

The journey began in 2019 when the estate’s new owner sought to address soaring energy bills and the deteriorating infrastructure of the house. The estate faced significant challenges, including outdated heating systems powered by inefficient LPG boilers and a defunct diesel generator. Consuming over 100 tonnes of carbon annually, the estate required a comprehensive overhaul to align with modern energy standards while maintaining its historical integrity.

The project pursued three key objectives:

1. Eliminate reliance on fossil fuels.
2. Create a replicable model for sustainable retrofits of heritage properties.
3. Reduce operational costs and carbon emissions dramatically.

To meet these objectives, the retrofit followed a holistic approach incorporating renewable energy sources, advanced heating systems, and fabric-first principles to enhance insulation and airtightness.

1. Renewable energy integration
   • Ground Source Heat Pumps: Trenches in the estate’s meadows house loops that supply renewable heating. The use of directional drilling minimised disruption to the landscape and protected the site’s archaeological and ecological features.
   • Solar Power: 130 kW of ground-mounted solar panels, discreetly located to preserve the estate’s historic aesthetics, generate clean electricity. Ground screws were used for mounting, eliminating the need for concrete and enhancing reversibility.
   • Battery Storage: A network of 12 Tesla Powerwalls ensures efficient energy storage and distribution, balancing the estate’s needs during periods of low solar generation.
2. Building infrastructure upgrades
   • All heating systems were replaced with efficient air-source heat pumps for sections of the estate with limited space for ground loops.
   • Retrofitting included underfloor heating and breathable insulation materials such as hemp and wood fiber. Limecrete floors and historic service routes were carefully utilized to minimize structural intervention.
   • Modern yet reversible solutions, like secondary glazing and slimline double-glazing retrofitted into original sash windows, improved energy efficiency without compromising aesthetics.
3. Smart systems and long-term planning
   • Simplicity was prioritized in operational design. Instead of complex building management systems, the estate opted for standard controls like Nest thermostats, ensuring ease of use and maintenance.
   • Specialist installers, rather than general consultants, were engaged to leverage the latest advancements in renewable technology.

Challenges and adaptations

The project faced numerous challenges, including shifting regulatory requirements, utility connection hurdles, and the complexities of retrofitting a Grade I listed building. National Grid constraints required a bespoke substation and underground cabling to integrate the new systems. Additionally, balancing the historic preservation guidelines with modern sustainability needs necessitated innovative, site-specific solutions.

Impact and outcomes

The results of the retrofit are impressive. The estate now operates with near-total energy self-sufficiency, generating more electricity annually than it consumes. In its first year of operation, energy costs plummeted from over £100,000 to just £500—primarily standing charges. Carbon emissions have been slashed, and the embodied carbon of the retrofit was offset within just two years.

The project has garnered widespread recognition, winning awards such as the Architects Journal Retrofit Reuse and the RICS Environmental Impact Award. Athelhampton House stands as a shining example of how heritage and sustainability can harmonize.

NICK JENKINS’ INTRODUCTION: INSIGHTS ON STRATEGIC ENERGY TRANSITIONS

Nick Jenkins opened the seminar with a personal and insightful reflection on his own experiences retrofitting Stockton House with renewable energy solutions, laying the foundation for the day’s discussions. As Chair, he set the tone for the event by addressing key themes, including the challenges of transitioning historic homes to sustainable energy systems and the importance of timing, practicality, and forward-thinking strategies.

How the seminar series began

• Nick shared how his collaboration with Moulding began during the 2014 restoration of Stockton House, which involved comprehensive renovations. Initially, he opted for a gas heating system due to skepticism about the viability of renewable options like ground-source heat pumps.
• Years later, after personally installing a ground-source heat pump system at Stockton, Nick and Tim Moulding recognized a gap in accessible, all-encompassing advice for country house owners navigating energy transitions. This realisation inspired the Strategic Energy Decision Making in Historic Houses seminar series.

Nick’s experience with Ground-Source Heat Pumps

• Motivation: Nick highlighted his desire to reduce his carbon footprint and avoid the contradiction of advocating for environmental causes while using a system that emitted 90 tonnes of CO₂ annually. The Renewable Heat Incentive (RHI) was also a key driver.
• Preparation: Before installing the system, Nick tested the house by lowering the heating circuit to 55°C to ensure it could operate efficiently with a heat pump. He found the house could maintain a comfortable 19°C without significant alterations, aside from two particularly exposed rooms.
• Operation and comfort: Post-installation, the house was heated consistently at 19°C, which proved more cost-effective and comfortable than intermittent heating. Consistent temperatures warmed the walls, enhancing overall efficiency and comfort.

Key lessons for Country House owners

1. Timing:
   • Major retrofits should align with broader restoration projects to minimise disruption and additional costs.
   • Even if a full transition isn’t feasible, owners should prepare their properties (e.g., sizing radiators for 55°C flow temperatures) for future renewable energy systems.
2. Economic considerations:
   • Decisions must account for fully loaded costs, including capital investment, operational expenses, maintenance, and potential subsidies.
   • Without subsidies like the RHI, the economics of such systems have shifted, but long-term savings and inevitabilities of electrification still make these investments worthwhile.
3. System design:
   • Nick chose vertical boreholes for his ground-source system to minimise land disruption.
   • Heat pumps, particularly ground-source, remain the most efficient and scalable solution for long-term decarbonisation in historic properties.

Reflections on Athelhampton House

• Nick expressed enthusiasm for Athelhampton’s innovative energy solutions, particularly the air-source heat pumps and battery storage systems. He noted that air-source heat pumps, traditionally associated with noise issues, demonstrated significant technological advancements in both efficiency and quiet operation during his visit.
• He also highlighted the potential for battery arrays to revolutionise energy management in country houses, balancing renewable generation with consumption needs.

Nick concluded by emphasising the inevitability of electrifying historic properties and the importance of taking proactive steps now to future-proof them for the coming decades. His thoughtful introduction framed the seminar as an opportunity to learn from practical experiences and cutting-edge solutions like those implemented at Athelhampton House. He then handed over to Bean Beanland to provide a broader national context for renewable energy transitions in historic buildings.

BEAN BEANLAND: THE NATIONAL CONTEXT FOR ENERGY TRANSITION

Bean Beanland, representing the Heat Pump Federation, delivered a detailed overview of the national context for energy transition, emphasizing the strategic decisions and challenges involved in decarbonizing the UK’s energy systems. He highlighted the broader implications for historic houses and private estates while exploring political, economic, and social drivers.

Strategic decision-making in a shifting policy landscape

• Past Incentives: Bean discussed how earlier policies, such as the Renewable Heat Incentive (RHI), drove decisions toward biomass systems, sometimes with poor long-term outcomes (e.g., skyrocketing pellet prices). With these incentives gone, strategic long-term planning is now critical.
• Policy shifts: The UK has seen delays and reversals in decarbonisation policies, such as pushing back bans on fossil fuel systems and diluting targets for achieving Net Zero by 2050. This lack of clarity has created confusion and slowed progress.
• Strategic importance: Decisions on energy transition require long-term thinking, particularly in estates and historic properties. Bean emphasised the importance of viewing costs holistically, considering both upfront investments and operational savings over decades.

Current energy challenges and progress

• Renewables infrastructure:
  • Offshore wind projects have gained momentum, though onshore wind faces resistance due to aesthetic concerns.
  • Subsea cables are being installed to improve energy transmission from renewable sources in Scotland to southern England.
• Solar power potential: Bean highlighted opportunities for expanding solar on agricultural and commercial roofs while minimizing land use for solar parks.
• Energy pricing: The UK faces a significant “spark gap,” with electricity costing four times more than gas. This disincentivises the adoption of heat pumps, as they must achieve over 350% efficiency to break even.

Historic and cultural shifts

• Heritage adaptation: Organisations like Historic England and the Church of England are now embracing renewable energy solutions, such as solar panels on Grade I-listed buildings and innovative heating systems using waste energy. Examples include:
  • Solar panels on King’s College Chapel in Cambridge.
  • Heat recovery systems in the historic Roman Baths in Bath.
• Public perception: Shifting attitudes toward renewable energy are critical. Bean advocated for addressing concerns about aesthetics and environmental impacts, such as the placement of wind turbines and solar parks, while focusing on the broader benefits of decarbonisation.

The path ahead

• Energy transition as an inevitable journey: Bean emphasised that decarbonisation is unavoidable. He called for clear government messaging to provide confidence and direction for individuals and businesses.
• Making it affordable: By spreading costs over time, much like the rollout of central heating in the mid-20th century, energy transitions can become accessible to more people. He highlighted the need for financial sector involvement and innovative funding models.
• Social and environmental good: Beyond financial considerations, Bean urged a focus on the social and environmental benefits of decarbonisation, framing it as an investment in future generations.

Key takeaways

• Decarbonising historic houses and estates is a strategic, long-term decision that requires clarity from policymakers, financial backing, and public support.
• While challenges like high electricity costs and resistance to renewable installations remain, technological advancements and shifting public attitudes offer hope for progress.
• By learning from successful examples, such as Athelhampton House, historic properties can balance sustainability with heritage preservation, contributing to broader national goals.

Bean’s talk provided a comprehensive overview of the national energy transition landscape, offering valuable insights for country house owners navigating this complex but necessary journey. His emphasis on long-term planning, innovation, and clear communication set the stage for further discussions throughout the seminar.

STEFAN PITMAN: LEADING THE ATHELHAMPTON RETROFIT

Stefan Pitman, director of SPASE Architects, provided an overarching perspective on the ambitious energy transition project at Athelhampton House. As the lead architect, he orchestrated the delicate balance between modern energy efficiency and heritage preservation. By integrating modern sustainability practices with sensitive heritage preservation, the project stands as a testament to how historic properties can evolve to meet contemporary energy needs.

Stefan detailed how the project began with the estate’s acquisition in 2019, when the new owner aimed to tackle failing infrastructure and high energy costs. The goal was to create a model retrofit that balanced sustainability, operational efficiency, and historical sensitivity.

• Multi-Phase Execution: The project spanned two main phases:
  • Phase 1: Focused on infrastructure, including ground-source heat loops, electricity upgrades, and initial heating systems for outbuildings.
  • Phase 2: Cantered on retrofitting the main house, including heating upgrades, insulation, and integration of renewable systems.

Challenges and problem-solving

• Heritage constraints: Athelhampton’s Grade I listed status required careful planning to ensure interventions were reversible, unobtrusive, and sensitive to its historical significance. This included consulting with Historic England early in the process.
• Dynamic adaptations: Stefan described how evolving challenges, such as National Grid limitations and shifting planning requirements, necessitated a flexible approach. For example, directional drilling was used to minimise disruption to the landscape and protect archaeological features.
• Avoiding overcomplexity: The project deliberately avoided overly complicated building management systems (BMS). Instead, they opted for user-friendly controls and modular designs that could be maintained locally without specialist expertise.

Technical achievements

• Energy generation and distribution: The project incorporated:
  • Ground-source heat pumps in trenches.
  • Air-source heat pumps for the main house due to space and cost constraints.
  • Solar panels (130 kW) mounted discreetly with reversible ground screws.
  • Tesla Powerwalls for energy storage and backup.
• Infrastructure overhaul: Upgrades included replacing failing plumbing, electrical systems, and heating, while also integrating insulation and underfloor heating into the building’s structure.
• Heat loss management: By insulating intermediate floors and using breathable materials like hemp and limecrete, the project reduced heat loss without compromising the building’s fabric.

Sustainability impact

• Carbon reduction: The retrofit reduced the estate’s carbon emissions from over 100 tonnes annually to near-zero. The embodied carbon from new systems was offset within two years.
• Cost savings: Energy costs dropped from £100,000 annually to just £500, primarily due to standing charges.
• Award-winning design: The project received numerous accolades, including the Architects Journal Retrofit Award and the RICS Environmental Impact Award.

Community and knowledge sharing

• Blueprint for others: Stefan emphasised that the project was intended as a model for similar heritage retrofits. By collaborating with specialists and sharing insights, the team sought to inspire and inform other property owners.
• Public engagement: Athelhampton’s role as a public site added layers of complexity to the retrofit, but it also allowed the estate to demonstrate the feasibility of sustainable transitions for historic buildings.

Following on from Stefan, the third speaker was Mike Stephenson, of H2Eco.

MIKE STEPHENSON: ADVANCING RENEWABLE ENERGY AT ATHELHAMPTON HOUSE

Mike Stephenson, representing H2Eco, played a pivotal role in designing and implementing renewable energy solutions at Athelhampton House. His expertise in renewable energy installation and commitment to decarbonisation were instrumental in overcoming the project’s technical and operational challenges. Here’s a summary of his key insights and contributions:

Philosophy and approach

• Decarbonisation focus: The project was guided by the principle of eliminating fossil fuel reliance entirely, simplifying decision-making and aligning with sustainability goals.
• Adaptable design: Given the rapid evolution of renewable technologies,
  the project avoided reliance on outdated methods or generalised consultant designs, favouring direct collaboration with manufacturers and specialist installers.

Heating systems

• Heat Pump choices: Multiple renewable heating solutions were evaluated, including air-source, ground-source, and water-source heat pumps.
  • Ground Source: Initially chosen due to financial incentives under the Renewable Heat Incentive (RHI) program, a shallow dig system was installed to serve River Cottage and other outbuildings.
  • Air Source: Later adopted for the main house due to space limitations and cost efficiency, with 15 high-efficiency air-source heat pumps providing redundancy and precise modulation to match heating demands.

Energy generation and storage

• Solar Panels: Solar arrays totalling 130 kW were strategically located to maximise generation without compromising the estate’s aesthetics.
• Battery Systems:
  • Nine Tesla Powerwalls handle energy storage and time-shifting, ensuring efficiency by storing solar power for use during high-demand periods.
  • An additional three Powerwalls act as a backup power source, replacing the estate’s previous diesel generator and providing resilience during outages.

Grid connection challenges

• A new substation and underground cabling were required to meet the estate’s power demands and enable surplus energy export to the grid. National Grid constraints posed logistical and financial challenges, requiring adaptive design solutions.

Operational simplicity

• Practical controls: Instead of complex building management systems, user-friendly Nest thermostats were installed to allow easy operation and maintenance.
• Standardised components: Systems were designed with widely available parts to ensure long-term serviceability, reducing reliance on bespoke solutions.

Long-term impact

• Performance and efficiency: The heating and energy systems have performed exceptionally, with heat pumps providing efficient, quiet, and reliable operation.
• Demonstration of value: The project showcases how renewable technologies can effectively decarbonise historic properties. It addresses misconceptions about heat pumps, particularly their suitability for older buildings, noise levels, and efficiency.

Mike emphasised the importance of collaboration between owners, architects, and installers in achieving a sustainable, functional design. His forward-thinking approach, combined with technical expertise, contributed significantly to Athelhampton’s success as a model for renewable retrofits in heritage properties.

To close the discussion, Sarah reflected on the importance of a fabric-first approach.

SARAH SMALL, PASSIVE HOUSE DESIGNER, SPASE: FABRIC-FIRST APPROACH TO RETROFITTING HISTORIC BUILDINGS

Sarah Small, a Passive House designer with SPASE Architects, highlighted the importance of a fabric-first approach in achieving energy efficiency in historic buildings. Drawing from her expertise and hands-on experience, she discussed innovative strategies and materials for retrofitting while preserving heritage integrity.

Fabric-first principles

Airtightness and insulation: Sarah emphasized that improving a building’s fabric – its walls, floors, and roofs – is crucial to reducing heat loss. By prioritizing airtightness and super-insulation, energy demand for heating can be minimized, even in historic structures.

Breathability of materials: Materials like hemp insulation, wood fiber boards, and recycled newspaper were used because they allow the building to breathe, preventing moisture buildup. This is particularly important in older buildings with solid walls.

Intelligent membranes: These advanced materials act like a breathable barrier (similar to Gortex) that prevents moisture ingress while allowing vapor to escape, maintaining a healthy internal environment.

Innovative retrofitting techniques

Underfloor heating: Limecrete floors with underfloor heating were installed to improve efficiency while respecting the building’s structural limitations. Sarah noted that even upper floors were adapted with innovative underfloor heating techniques, avoiding damage to original timbers.

Cold bridging solutions: To prevent heat loss through structural elements, insulated raft foundations and detailed retrofitting around cold bridges were used, particularly in areas where traditional insulation methods weren’t viable.

Use of natural and recyclable materials: Sarah highlighted the use of modern sustainable materials, including recycled newspaper for insulation and new advancements like cork and lime plaster.

Challenges in retrofitting historic buildings

Moisture management: A significant focus was on avoiding moisture risks that arise when adding insulation to historic walls. Sarah explained that carefully designed cavities and breathable materials were critical to maintaining the natural balance of the structure.

Compatibility with heritage features: Solutions were tailored to integrate with the building’s historical architecture, ensuring that retrofitting efforts respected the original fabric.

Broader vision for retrofitting

Learning from Passive House standards: Sarah described how principles from Passive House designs – such as airtightness, high insulation, and energy efficiency – were adapted for historic properties. These methods aim to achieve net-zero carbon while preserving heritage value.

Scalable innovations: She mentioned her experience with Victorian school buildings and noted how similar retrofitting approaches could be scaled for other heritage properties.

Key takeaways

Sarah’s insights underscored the importance of thoughtful design, material selection, and a sensitivity to historic integrity when retrofitting older buildings. Her expertise ensured that Athelhampton House balanced sustainability with heritage conservation, setting an example for how the built environment can evolve to meet modern energy needs.

After Sarah’s talk, the discussion was opened up to the audience for Q&A with the expert panel.

AUDIENCE PARTICIPATION:
QUESTIONS AND ANSWERS

The audience played an active role in the discussion, asking insightful questions that provided further clarity on the technical, financial, and practical aspects of the Athelhampton House retrofit project.

The audience’s questions helped illuminate the thought process behind critical decisions in the project, from technical choices like heat pump configurations to broader issues like cost-effectiveness and energy efficiency. The answers provided valuable insights into how the Athelhampton retrofit balanced sustainability, practicality, and heritage conservation.

1. Retrofitting vs. new build costs

• Question: How do the costs of retrofitting compare to building a similar space from scratch?
• Answer (Stefan Pitman): Costs vary depending on the building’s fabric and specifications. In many cases, retrofitting can be comparable to new builds, but the outcomes depend on the complexity of the retrofit and preservation requirements.

2. Improving historic windows

• Question: How can energy efficiency in historic windows be improved?
• Answer (Stefan Pitman): Historic England has become more accommodating. For instance, slimline double glazing can be retrofitted into existing sashes, and secondary glazing is now often permitted. These upgrades enhance thermal performance while maintaining the original appearance.

3. Carbon cost and payback

• Question: What is the carbon cost of installing the new systems, and how does it compare to modern gas systems?
• Answer (Stefan Pitman): The embodied carbon from manufacturing and installing the systems was offset within two years through energy savings. While modern gas systems are more efficient than older ones, they still cannot compete with the efficiency of heat pumps, which achieve up to 400% efficiency.

4. Ground Source vs. Air Source costs

• Question: How do ground source and air source systems compare in terms of capital and operational costs?
• Answer (Mike Stephenson): Ground source systems require higher upfront investment but have a longer lifespan and lower running costs. Air source systems are less expensive to install but are equally efficient in operation. For Athelhampton House, air source was selected for the main building due to space and cost considerations.

5. Energy self-sufficiency

• Question: Is the estate fully self-sufficient in electricity, and how have rising energy costs affected operations?
• Answer (Stefan Pitman): Over the year, the estate generates more electricity than it uses, aided by battery storage for time-shifting. The energy bill has dropped to just £500 annually, mostly due to standing charges, despite high energy prices.

6. Timing of insulation work

• Question: Why wasn’t insulation completed before establishing heat loss requirements?
• Answer (Stefan Pitman and Mike Stephenson): Heat loss calculations included projections for planned insulation improvements. Phase 1 focused on infrastructure and energy generation, while insulation upgrades were carried out during Phase 2 alongside refurbishments.

7. Achieving target temperatures

• Question: Were the target temperatures achieved, especially in extreme weather?
• Answer (Stefan Pitman): Yes, the house maintains 18°C in common areas and 21°C in living spaces, even at external temperatures of -4°C. This was achieved despite limitations in insulating certain heritage features like the Great Hall roof.

8. Maintenance and longevity of systems

• Question: How long do the heat pumps last, and what is the service requirement?
• Answer (Mike Stephenson): Heat pumps have a service life of about 20 years, with routine maintenance like filter and fan replacements. They are serviced annually, and the modular design ensures redundancy if one unit fails.

9. Simplified controls and specialist installation

• Question: Was it a mistake to avoid hiring a mechanical and electrical (M&E) consultant?
• Answer (Stefan Pitman and Mike Stephenson): No. The team’s direct collaboration with specialist installers ensured up-to-date solutions. This approach avoided the potential lag in knowledge typical of M&E consultants, given the rapid evolution of renewable technologies.

10. Efficiency of intelligent membranes

• Question: Are intelligent membranes an insulation product?
• Answer (Stefan Pitman): Intelligent membranes manage air and moisture movement rather than providing insulation. They enhance airtightness while allowing the building to breathe, a critical feature for heritage properties.

A MODEL FOR THE FUTURE

Athelhampton’s retrofit underscores the potential for deep retrofitting historic buildings to meet modern energy demands. Through collaboration, innovative technologies, and sensitivity to the site’s historical and environmental context,
the project has created a replicable model for other listed properties.

For architects, conservationists, and property owners, Athelhampton House proves that energy transitions in heritage buildings are not only feasible but also transformative – economically, environmentally, and culturally.

LOOKING AHEAD: JOIN US FOR THE NEXT SEMINAR

The overwhelmingly positive response to the Strategic Energy Decision Making in Historic Houses seminar series has inspired Moulding to continue this journey. Attendees at Stockton House and Athelhampton have been thrilled by the depth of insights, practical advice, and inspiring examples shared. With such enthusiasm from the audience, we’re delighted to announce that another seminar will take place this year.