The first homes Bellway has built to highly energy efficient Passivhaus Standard have passed their final airtightness tests, comfortably exceeding the requirements for Passivhaus certification.
The housebuilder is delivering eight two-bedroom Passivhaus properties at its Perceval Grange development in Midhurst, West Sussex.
Final airtightness testing has now been carried out on the first block of four terraced houses, which achieving an overall airtightness level of 0.391 air changes per hour (ACH) at a pressure of 50 Pascals. Passivhaus Standard requires a level of 0.6 ACH@50Pa, while for comparison a typical Bellway house has an airtightness of 4.5.
The first four Passivhaus homes at Perceval Grange are due to be completed and ready for occupation in September, with construction of the second block of four Passivhaus plots ongoing.
Bellway Group Head of Technical and Innovation, Jamie Bursnell, said: “Bellway inherited the planning requirement to construct eight homes to Passivhaus standard on acquiring the land for Perceval Grange, and we have used this as an opportunity to find solutions, upskill our workforce and gain insights into how ultra-airtightness can be delivered at scale.
“With supply chain partner Donaldson Timber Systems, we took a value engineering approach to review and redesign the building fabric with the combined objectives of delivering the U-value required and making the homes as affordable as possible.
“We also worked closely with Aeroseal UK, using their Aeroseal Technology Process to automatically find and fill air gaps in the building fabric, and AES Sustainability, who supported us throughout the certification process from design to final testing.
“The key takeaway from the project is 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 the construction of homes by Bellway teams across the UK, as the forthcoming Future Homes Standard building regulations are introduced to reduce carbon emissions generated by the nation’s homes.”
The Passivhaus plots require very low energy use because of their airtightness and thermal performance. They are constructed with a highly sustainable pre-insulated timber frame wall panel – with the use of timber in itself delivering embodied carbon benefits – and an inner air barrier membrane.
Heat loss from thermal bridging – when more conductive materials such as steel or concrete slabs penetrate the insulation – is reduced to an absolute minimum, through the careful consideration of how junctions are constructed and the use of external doors and triple-glazed windows with high thermal performance.
Mechanical Ventilation and Heat Recovery (MVHR) systems use the warmth created in kitchens and bathrooms to heat other areas such as living rooms and bedrooms, cutting demand for energy to heat those spaces.
The energy which is required to heat the Passivhaus plots comes from all-electric air source heat pumps (ASHPs), even though Passivhaus certification can be achieved in homes heated by gas boilers. Solar panels are also incorporated into the roofs of the Passivhaus plots at Perceval Grange for the generation of renewable energy.
Other sustainable features include rainwater harvesting to provide water for running washing machines and flushing toilets, and brown roofs to car ports to support biodiversity.
There are eight Passivhaus plots being built at Perceval Grange – each in the two-bedroom Bepton house style – with seven for private sale, priced from £399,995, and one affordable home for shared ownership.
For more information, visit https://www.bellway.co.uk/new-