ANALYSIS  ⁄  PLANNING & PLACE

Exeter net zero housing revolution takes root in Chestnut Avenue

Exeter City Council is taking exploratory steps from talking about a zero carbon future to delivering one with a pilot housing project in Wonford.

EXETER CITY COUNCIL   NET ZERO EXETER   CLIMATE CRISIS   HOUSING   RETROFIT   PLANNING POLICY   PRIORY  

The green shoots of a net zero housing revolution are to be found on Chestnut Avenue, in Exeter’s Wonford housing estate, where six of the city’s 5000 council-owned homes have been chosen to pilot a new approach to transforming existing houses into energy efficient, low maintenance homes.

The pilot has been developed by the city council in partnership with others including a company called Energiesprong UK. “Energiesprong”, which translates literally as “energy jump”, is the trade name of a commercial process for retrofitting existing houses to net zero carbon standards that is already well-established in the Netherlands.

As the Energiesprong concept arrives in the UK, with projects for Nottingham and Exeter councils and a housing association in Essex, the pilot puts Exeter among the front-runners on the long march to a net zero carbon future.

Exeter net zero carbon housing pilot project in Chestnut Avenue

Retrofitting existing housing stock to eliminate the residential sector’s contribution to climate-changing carbon emissions is critical. The latest figures show that residential property accounts for 18% of the UK’s total CO2 emissions, a proportion that has risen steadily over the past ten years as the business and energy supply sectors have made more rapid progress in decarbonising.

Averaged UK figures show that space heating is the dominant driver of energy consumption in existing homes, making up 63% of annual energy consumption, followed by hot water demand (17%) and appliance demand (13%).

So, to meet Exeter City Council’s target of reaching net zero carbon emissions by 2030, urgent action is required to transform the city’s 50,000 homes.

The Chestnut Avenue pilot is both a demonstration of what retrofitting can achieve and, crucially, a source of learning to inform future investment decisions on a wider programme.

Exeter net zero carbon housing pilot project in Chestnut Avenue in Wonford

The Energiesprong concept is simple enough. A new outer shell is placed over an existing house. All the parts are precision-made in a factory before being brought to the conversion site. Wall panels are manufactured with integrated windows and doors, and are pinned directly to the existing outer walls. Roof tiles are replaced by a lightweight covering on top of which solar panels are laid together like tiles to keep the rain out.

The finished conversion requires no gas supply, and guarantees minimum temperatures and markedly reduced energy bills. The Green Alliance has produced a report which describes the process in more detail and assesses its potential.

With an experienced contractor a single house can be converted in as little as a day. However, while the six Chestnut Avenue houses selected for the pilot are arranged in a row of three adjacent semi-detached buildings, and all in council ownership, the pioneering nature of the project, combined with December’s wet weather, meant it has taken nearer four months to convert them.

Exeter net zero carbon housing pilot project external cladding and solar roof closeup

Ian Hutchcroft from Energiesprong UK recently delivered a seductive sales pitch to a thinly attended meeting of the city council’s Strategic Scrutiny Committee. He said three key conditions need to be met for the industry to take off in the UK.

First, a radical change in the purchaser-contractor relationship is required, from one in which the purchaser specifies a lot of detail to one where the purchaser specifies the outcomes to be achieved and leaves it to the supplier to decide how to achieve them.

Second, a shift to lower energy costs for tenants, because they need to consume less energy, is needed to allow a higher proportion of total housing payments to go to the landlord, in this case the council, to build up capital for future retrofits.

Third, the market for retrofits must become sufficiently large to encourage investment in the capacity to manufacture the parts needed for conversions at scale, thus reducing costs.

Exeter net zero carbon housing pilot project Mi-Space sign

The Chestnut Avenue retrofit is being carried out by Mi-space, an arm of the West Country-based Midas Group. But the project’s scale is tiny compared to the cost-efficient volumes needed to lower prices enough to persuade private sector landlords and owner occupiers, as well as councils and housing associations, to pay for conversions on a significant scale.

The Dutch experience was that institutional landlords needed to club together to create a sufficiently large customer base to justify the investments in manufacturing that are required. In the UK co-operatives could also be established to help owner-occupiers and private landlords take advantage of such economies of scale.

The principle is that the conversions pay for themselves through reduced energy and maintenance costs. But capital is needed upfront. Exeter has 50,000 houses of which only 10% are owned by the council. The city’s chief executive, Karime Hassan, tweeted after the scrutiny meeting that retrofit has the potential to help meet the city’s aim to be carbon neutral by 2030, but that scaling up from the pilot would be a challenge.

Exeter net zero carbon housing pilot project Karime Hassan tweet

It’s not only money that could hold back a programme like this. Owner-occupiers will need to decide whether they will stay in their homes long enough to benefit from the payback on the capital outlay, and older people may decide it’s not worth it.

Will private sector landlords, who currently simply pass on energy costs to their tenants, consider conversions value for money? Will the UK’s profit-driven construction industry be prepared to take on new types of outcome-based contract requiring 30-year guarantees? Will the government be prepared to toughen up building regulations to force house builders to adopt Passivhaus or similar standards and apply them retrospectively over time?

The benefits of major retrofitting programmes appear substantial, not only in terms of meeting our carbon targets but also because they create badly-needed new jobs in the manufacturing and construction sectors to replace those displaced from climate-hostile industries.

Whether Exeter adopts the Energiesprong model or something similar, the time available to convert the city’s existing housing stock is short. Council officers are enthusiastic about the Chestnut Avenue pilot, but they know that they, as well as councillors, will have to make hard-headed decisions on the way forward.

Initial conclusions from the pilot project are expected by Easter 2020.


 is a contributing editor of Exeter Observer.

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