The energy efficiency of UK housing is very poor, contributing significantly to carbon emissions, and around 13% of households are living in fuel poverty. It’s vital that new houses are built to higher standards, so they don’t need costly retrofitting in the future.
City of York Council is building 600 ‘zero carbon in use’ homes – properties that can be warmed and supplied with electricity and hot water without generating carbon emissions. The homes will be built to Passivhaus certification, a standard that leads to very little heat loss. Air source heat pumps will be used for heating and hot water, with roof-mounted solar panels supplying electricity.
The programme includes 600 homes across a number of council-owned sites. Two of these sites are in the planning process with construction due to start in early 2022 with first handovers by the end of the year. The homes will be in tight-knit terraces, improving their energy efficiency, and will be positioned to create maximum solar gain. The council is taking a holistic approach to make these developments truly sustainable, also offering car-free streets, free use of shared e-cargobikes and planting schemes that increase biodiversity. The development will include homes for private buyers, social rental and shared ownership.
An average new build home emits around 1.5 tonnes of carbon dioxide (CO2), so the annual carbon savings from energy use for the whole programme will be 900 tonnes. The council has also considered embodied carbon in the design process. This is all the carbon emitted to produce the materials for construction and is usually neglected in carbon calculations for new buildings. In one instance this approach helped save a forecast 120,000Kg of CO2 equivalent (Co2e) just by changing the foundation design on one of the schemes.
Lower energy bills
The energy used in each home will be far lower than for a standard new build property. Over the course of a year each home will generate at least as much energy as it uses, and many properties will actually create a surplus. Due to this, total energy bills will be more than 50% lower than those for a new property built to standard building regulations (around £395 per year rather than £723). 40% of the homes on each site will be affordable, so this saving will greatly help tackle fuel poverty for those residents and increase their disposable income.
Improved resident health
The project is expected to improve people’s health by encouraging active travel, and by providing warm, well-ventilated homes.
Upskilling of local workforce
City of York Council is using grant funding (from the Local Government Association) to work with a local college to train up lecturers on Passivhaus, and to offer conversion courses that help local gas engineers work on heat pumps.
The project aims to increase biodiversity in the area by ensuring that the landscaping around the houses is good for wildlife.
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The project started in 2017 as a build of standard affordable housing. However, following the council elections of 2019, the new Green Party/Liberal Democrat coalition was keen to deliver net zero carbon in-use across all developments, in line with York’s climate emergency declaration, which sets a target of 2030 for the city to reach net zero emissions.
A robust business case
Building an entire development of homes that are net zero in terms of carbon emissions is more expensive, and therefore potentially costlier for residents to purchase or rent. By using new market sales to subsidise the cost of 40% of the homes, 20% will be affordable for social rent and 20% will be affordable for shared ownership.
Learning from best practice
Council officers carefully recruited a multi-disciplinary design team that would work on the scheme for at least five years. By setting ambitious goals and embedding design principles at the heart of the procurement plan, City of York Council was able to attract more specialist consultants. Architects Mikhail Riches are leading the project, having previously delivered the award-winning Norwich Goldsmith Street project. This multi-disciplinary team have now developed a detailed technical design for the project.
The development uses pre-made timber frames which makes the project lower risk for contractors; the project is also exploring other innovations such as more permeable paving and non-concrete drains.
Communities have been heavily involved in designing the scheme. Each scheme involves three stages. Co-producing the Duncombe Barracks development, for example, involved a day-long interactive workshop at a local church. This featured a detailed design workshop with briefings from the design team in the morning, followed by a hands-on modelling session in the afternoon with inspiration from over 200 drawings provided by the children from a local school.
Building local skills
York’s programme aims to give more local people the skills to work in sustainable building. The procurement process incorporated skills development for contractors, who were asked how taking part would increase green skills. The council set out minimum requirements for supporting skills and apprenticeships. Contractors also agreed to spend a minimum number of hours supporting the local college in teaching green skills.
Contractors also had to input into the design of new college courses on Passivhaus approach. The council was also able to obtain grant funding from the Local Government Association to train local tradespeople on solutions such as air source heat pumps. The council has established a stakeholder group with local colleges focussed on sustainable building, which involves both the council’s housing and skills team.
As City of York Council was starting from scratch on this programme, the initial sites have required considerable time and effort to design, and design fees were higher than previous new build schemes – adding 3% to build costs.
The Passivhaus standard adds around 10-15% to the basic build cost of a property, with use of a timber frame resulting in additional cost pressure due to recent material price inflation. Solar panels have become much cheaper in recent years but as these are so heavily used in the developments, they add £4000-5000 per property. The renewable heating units (Air Source Heat Pumps) are the most expensive piece of kit and full supply and installation of ducting can be around £10,000.
There have not been any specialist eco grants for new build properties, but City of York Council is working with Homes England who are keen to support their zero carbon approach. This has helped the council unlock extra Affordable Homes Programme grant funding. The scheme is funded through a mix of Right to Buy receipts, Homes England funding and market sales.
Consider communal heat pumps to reduce costs
The main challenge is achieving a net zero standard that’s affordable and can be scaled up for big developments of houses. Technology such as mechanical ventilation units, air source heat pumps and solar panels all drive up costs.
Sourcing air source heat pumps that are sufficiently small (heat demand is very low due to Passivhaus standard) is challenging, and communal air source heat pumps may be more effective.
Focus on the Passivhaus design principles to keep costs down. The council originally added three storey dormers to some properties for design purposes but this altered the buildings’ thermal envelope and meant significantly more insulation. Sticking to simpler building forms reduces the need for insulation.
Training in green construction skills will be key to future projects, working with colleges is key
Contractors are not experienced in delivering Passivhaus projects at scale. As well as this, college students are not aware of the green construction skills they will need in the future. For example the local college was considering closing its plastering course which is a key skill for external wall insulation. Including local colleges as project stakeholders is helping to address these issues.
Bringing other council departments on board is important. The project took a novel approach to development which was not always aligned to existing council design guidelines. Differences included designing for low parking demand, including more footpaths, and using sustainable urban drainage (SUDS) rather than the standard concrete drains. The project team has worked closely with the Highways team, bringing in suppliers of new technologies and at times using political leverage to emphasise the importance of an innovative low-carbon approach.
Higher national standards, set by government would reduce the challenges faced by the council
The project was vulnerable to risk pricing (contractors increasing their prices due to uncertainty) and there was potential for quality issues on site. Higher building costs make it difficult to compete for new land that comes up on the open market, as other developers with lower build costs can offer higher prices. Further regulation from government is needed to set higher build standards.
The project design guide is available online.
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