Projects

As the housebuilding sector continues to explore practical routes to lower-carbon construction, Bellway’s first Passivhaus project marks an important milestone.  Located at its award winning Perceval Grange in Midhurst, West Sussex, comprises eight Passivhaus homes within a wider 69-home development and represents a significant step towards the mainstream adoption of ultra-low-energy housing. While the development was initially driven by planning requirements within the South Downs National Park - where developments of more than 10 dwellings are required to deliver 10% of homes to Passivhaus standards - it has become a valuable demonstration of how Passivhaus principles can be delivered successfully within a volume housebuilding environment. The scheme highlights the growing commercial viability of Passivhaus as a practical solution for reducing operational carbon emissions while improving comfort and energy efficiency for homeowners.

Consultants AES Sustainability was appointed by Bellway to support them throughout the project, providing specialist Passivhaus consultancy, performance modelling, technical guidance and certification management from design through to construction. Working alongside Bellway and FBB Architects, AES played a key role in developing a buildable and cost-effective strategy capable of achieving the demanding requirements of Passivhaus certification.

One of the earliest challenges was determining how best to achieve the required levels of thermal performance and airtightness while maintaining a construction approach that Bellway could confidently deliver. Drawing on experience gained across the Passivhaus sector over the last decade, AES recommended timber frame construction as the most effective route forward. The use of an offsite, factory produced closed panel system provided a highly controlled construction method, offering consistent insulation performance and reducing the risks commonly associated with achieving exceptionally low levels of air leakage on site. The approach gave Bellway greater confidence that the performance targets could be achieved while keeping the project commercially realistic.

Throughout the design process, AES undertook detailed PHPP (Passive House Planning Package) modelling to assess and optimise the building performance. PHPP is the industry-standard software tool used for Passivhaus projects and enabled the team to evaluate different design options, insulation specifications and construction details before work commenced on site. The modelling process also proved invaluable during construction. Minor changes inevitably arose as the project progressed, including adjustments to window positions, and AES was able to rapidly reassess factors such as solar gain, shading performance and thermal bridging to ensure the homes remained compliant while allowing practical construction decisions to be made on site.

Thermal bridge analysis formed another important element of AES’s role. Achieving Passivhaus certification requires careful consideration of every junction within the building envelope to eliminate unnecessary heat loss. AES carried out detailed thermal bridge calculations and worked closely with the wider design team to ensure that connections between walls, roofs, floors, doors and windows met the required performance standards. Combined with the heavily insulated building fabric and high-performance triple glazing incorporated into the homes, this approach helped create a highly efficient thermal envelope.

Airtightness represented one of the most critical performance measures on the project. To further de-risk delivery, Bellway worked with Aeroseal UK, a specialist airtightness provider that uses and innovative technology that pressurises the building and releases a fine aerosol sealant which automatically identifies and seals air leakage paths.

Initial results have exceeded expectations. Airtightness testing carried out on the first block of four homes achieved an impressive result of just 0.39 air changes per hour, significantly outperforming the Passivhaus target of 0.6 air changes per hour. Achieving approximately half of the allowable target demonstrates not only the effectiveness of the construction strategy but also the quality control measures implemented throughout the project.

While Passivhaus is often associated with energy efficiency, occupant comfort is equally important. To support this objective, the Perceval Grange homes incorporate Mechanical Ventilation with Heat Recovery (MVHR) systems, which continuously supply fresh filtered air while recovering heat from extracted air. These systems help maintain excellent indoor air quality and comfortable internal temperatures throughout the year while minimising energy demand. AES provided extensive site support during installation and commissioning, carrying out regular visits and working with contractors to ensure the systems operated correctly and complied with certification requirements.

The homes also incorporate low-carbon air source heat pumps, reflecting Bellway’s wider commitment to reducing operational carbon emissions across its developments. As the Passivhaus fabric dramatically reduces heat demand, the heating systems can be significantly smaller than those typically required in conventional homes, delivering further operational efficiencies while maintaining comfortable living conditions for occupants.

Beyond the technical design work, AES has played a central role in managing the complex certification process. Passivhaus certification requires the submission of a substantial body of evidence demonstrating that the completed buildings match the approved design and meet the required performance standards. Throughout construction, AES has been responsible for collecting and coordinating site photographs, construction records, product certification, performance data, test results and installation evidence. This information has been compiled and submitted to the Passivhaus certifier, with the first block currently progressing through the final stages of review ahead of formal certification.

Bellway Group Head of Technical and Innovation, Jamie Bursnell, said: “Delivering the Passivhaus plots at Perceval Grange has been an exciting opportunity for the Bellway team to expand its knowledge and build expertise in delivering exceptionally energy-efficient homes. The support of industry partners including AES Sustainability, as well as Donaldson Timber Systems and Aeroseal UK, has therefore been invaluable to the success of the project.

“We have taken a collaborative approach from design through to construction and focused on upskilling the entire team to ensure everyone understands the standards required.

“We have learned that the two main elements required for airtightness are: simplicity of design to minimise potential gaps in the air barrier: and attention to detail to ensure that no gaps are created or missed.

“We are delighted at the excellent test results that the team on site have achieved here, but more significant is the fact that lessons learned at Perceval Grange will inform construction practices by Bellway teams across the UK, as we prepare for the introduction of the Future Homes Standard and continue our work to reduce the carbon emissions generated by the homes we build.”

For Bellway, Perceval Grange represents far more than simply achieving compliance with a planning requirement. It offers valuable experience in delivering Passivhaus homes within a mainstream housing development and provides a blueprint for how similar projects could be delivered in the future. As planning authorities, regulators and homebuyers increasingly prioritise energy efficiency and carbon reduction, the project demonstrates that Passivhaus can be incorporated into large-scale residential developments using proven construction techniques and commercially viable delivery methods.

By providing specialist modelling, technical guidance, thermal bridge assessments, airtightness expertise, on-site support and certification management, AES has helped Bellway transform its first Passivhaus scheme into a showcase for high-performance housing. The development stands as an important example of how collaboration, evidence-led design and practical construction solutions can deliver genuinely low-carbon homes while maintaining the commercial realities of modern housebuilding.