Demonstrate that the technology is available to deliver operational net zero homes at scale, to support Barratt Developments’ goal of all new homes being zero carbon from 2030.
Darren Evans provided consultancy and calculation services to support Barratt Developments, the developer delivering the scheme, and the architect responsible for producing the working drawings. Those services were:
Image provided from Barratts Zed House Project Brochure
Energy efficiency advice, SAP calculations and modelling work provided by Darren Evans helped Barratt Developments to make the ‘Zed House’ net zero home concept a reality. Zed House is the first new home in the country, built by a major housebuilder, that could be expected to go beyond the new Future Homes Standard.
Barratt has previously announced that all its new homes will be zero carbon from 2030. The Zed House concept is the first step to achieving that, demonstrating that not only is an operational net zero home possible, but that the building fabric and services specification can eventually be delivered at scale.
Thanks to an existing relationship where they provide advice and modelling to Barratt around new regulations, Darren Evans was a natural choice of partner for the Zed House. Barratt worked with more than 40 leading organisations from across the housebuilding, sustainability, and technology sectors to realise the project.
At the time the Zed House specification was being developed, the applicable energy efficiency regulation in England was Part L 2013. An intended update to the regulation, Part L 2021, had also been published in some detail, though not formally finalised at the time of the exercise.
As a stepping stone to the Future Homes Standard, Part L 2021 will deliver a 31% improvement on Part L 2013. The Future Homes Standard, meanwhile, due for implementation in 2025, has been earmarked to deliver a 75 to 80% improvement over Part L 2013.
The brief given to Darren Evans was to model the performance of the Zed House against both Part L 2013 and Part L 2021.
“Part L 2021 hadn’t gone live, so the energy performance certificate (EPC) for the property was lodged in accordance with Part L 2013,” explained Brandon Wipperfurth, Senior Sustainability and Energy Consultant at Darren Evans. “Overall, the Z House achieved a 125% reduction in carbon emissions.
“That means 100% of regulated emissions are met by the proposed specification, with the remainder helping to meet the unregulated emissions that result from occupant behaviour. Part L 2021 aims for 31% better than Part L 2021, and the design still met the net zero criteria of the brief.
“It’s the best-performing single house I’ve ever worked on,” added Brandon, “and as a result it is also set to exceed the requirements of the Future Homes Standard.”
Before the performance of the Zed House could be modelled, the specification had to be generated. Thanks to their existing relationship with Barratt Developments, Darren Evans was already familiar with the Alderney house-type specification that would form the basis for the Zed House.
“We started playing with the existing house type,” said Brandon, “and gave Barratt six or seven different options that would ensure the Zed House achieved a minimum 100% emissions reduction. We then ran live workshops with the project team to settle on a build spec that they were happy with.”
“Darren Evans offered a fantastic bespoke service,” said Danielle Michalska-Morris, Group Technical Innovation Manager at Barratt Developments. “They were extremely professional, and nothing was too much trouble. Brandon, specifically, went above and beyond. He is extremely knowledgeable and provided key support throughout the project in the delivery of a final compliant specification.”
Barratt Developments already knew they wanted to include low carbon heating in the form of a heat pump, and solar photovoltaics (PV) on the roof. This mechanical and electrical approach is what will allow volume housebuilders to eventually deliver net zero consistently and reliably.
Beyond the fundamental specification, the project has already identified key challenges around supply, installation and customer integration, which industry needs to address before net zero specifications can be delivered at scale.
A key part of Darren Evans’ role was refining the building fabric specification to ensure the mechanical systems did not have to be over-specified.
“We really helped with value engineering the U-values to achieve the required outcome while ensuring practicality,” said Brandon. “The floor and roof U-values are really good. We based the external wall on their typical 140mm deep timber stud to achieve a good balance between gaining more performance while keeping the overall wall thickness to a level that Barratt were comfortable with.”
Addressing thermal bridging heat losses is a critical part of achieving the required energy efficiency and comfort from modern homes. All housebuilders, regardless of their size, will need good thermal bridging detailing to meet the changing regulations and to keep specifications cost effective.
Psi values measure thermal bridging heat losses, and the Zed House’s psi values are low. The detailing is “clean”, to use Brandon Wipperfurth’s description, while airtightness has been improved over a typical property to further limit the loss of heated air.
Under proposals drawn up by a previous government, 2016 would have seen all new homes being built to a ‘zero carbon’ definition. Theoretically, then, could the Zed House have existed before now?
Fundamentally, yes, it could have - but the specification would have looked different. For example, the efficiency of solar PV has doubled in ten years. It’s now possible to achieve a net zero specification with panels covering 20m2 of roof area, where 40m2 would have been required before. Such a solution likely wouldn’t have been feasible, and it is these sorts of developments that make the Zed House concept better suited to being rolled out more widely.
As the electricity grid continues to decarbonise and carbon factors for electricity lower further, specifications can be refined and optimised to use resources more efficiently than they would have been previously.
For the actual construction of the Zed House, Darren Evans did not have to provide a usual level of consultancy for the on-site team. The home was designed so holistically up front that the contractor simply executed the project in accordance with Barratt’s requirements.
“I didn’t have to speak to the contractor during the build,” Brandon explained. “Normally that back and forth would be there, with them looking to make changes or use alternative products. But Barratt Developments were so prescriptive with the specification that there was none of that.”
Key to achieving genuine zero carbon homes is ensuring that the modelled performance is delivered in reality. To that end, an academic from the University of Salford will live in the house, and energy use will be monitored, measured and displayed live for visitors to see.
“True ‘operational net zero’ homes on a large scale will depend on accounting for occupant behaviour,” said Brandon in conclusion. “The year-long monitoring and evaluation of the Zed House will really show what has worked, and where improvements can be made, ready to be able to roll this out across the country.”
Darren Evans can help you on your journey to achieving construction projects with reduced environmental impact. Working with you from the earliest stages of the project, we can help you to refine building fabric specifications, analysing and quantifying carbon and energy reductions to achieve your assessment goals. To find out more about achieving your net zero ambitions, and exceeding sustainability requirements without excessive costs, explore our blog or contact us.
More than 100% reduction in regulated carbon against both Part L 2013 and Part L 2021. As a result, the Zed House would also be expected to surpass the intended Future Homes Standard, due to be implemented in 2025.
“It’s the best-performing single house I’ve ever worked on.” - Brandon Wipperfurth, Senior Sustainability and Energy Consultant at Darren Evans.
“Darren Evans offered a fantastic bespoke service. They were extremely professional, and nothing was too much trouble. Brandon, specifically, went above and beyond. He is extremely knowledgeable and provided key support throughout the project in the delivery of a final compliant specification.”
