Nottingham City Homes was the first housing association in the UK to pilot net-zero retrofits using the Energiesprong approach. The initial 10-home pilot project in 2017 was delivered by Melius Homes, designed by Studio Partington and funded by the Horizon 2020 REMOURBAN and Transition Zero projects. In 2021, this scheme was chosen as one of 17 exemplary projects for UKGBC's Build Better Now virtual exhibition as part of COP26. ‍

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The challenge – cold, draughty homes with an inefficient design

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The pilot scheme comprised 10 homes (a mix of terraces and bungalows) in Sneinton, on the edge of a city centre regeneration area.

While they were well located and had a great community, these concrete cross wall properties were freezing cold and tenants said external walls felt as though they moved when they leant on them!

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The design of the houses was very inefficient, with an unheated garage space under the living room, and an undercroft below the kitchen. This made both main living rooms particularly cold. The houses were also deep and narrow with internal staircases, and therefore had very minimal natural light in the main stairwell.  

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“It’s made a lot of difference. It’s warmer. I don’t need my dressing gown now. All the draughts have gone. Before it [the home] looked like a rabbit hutch – it looks like a proper home now” Joan Warbuton, Nottingham City Homes tenant.

The solution – a tenant-focused, highly energy efficient whole house retrofit

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The Solution Provider, Melius Homes Ltd, was procured to deliver the Energiesprong performance outcome including 1500kwh net import, a maximum tenant cost of £330 p/a (2018 tariffs) and guaranteed comfort for tenants.  

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The Energiesprong solution was procured based on a fixed price, evaluating instead the whole life cost and the design quality. The tenants were involved in developing the design brief, which means that the solution provider was able to include small additional items which made a big difference to the tenants’ lives, such as the light tubes making stairs brighter, outside taps for watering plants and a doorbell.

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Prefabricated off-site, wall panels arrived in ‘full storey heights’ complete with ample insulation, double glazed windows and a durable board finish, ready to crane into place. Tenants were able to remain in residence throughout the retrofit, which was completed in one week.

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"Our MMC advanced panelised system for deep retrofit and low energy new build homes has been developed over the past 6 years using continuous learning from the Energiesprong pilot projects. During this time we have achieved significant productivity and performance gains with a typical installation period reduced by 60% and cost reduction of circa 45%." Rob Lambe, Managing Director of Melius Homes

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Full list of measures

• External walls: Offsite manufacture facades from a range of suppliers, with Melius Homes now manufacturing timber frame with weather board cladding and mineral wool insulation.
• Roof: New cassette roofs with in-roof solar.
• Windows: Double glazed high performance.
• Doors : Amended only where not already renewed to composite doors.
• Heating power: Communal energy system in first 3 phases with GSHP. GSHP with individual heat pumps in fourth phase. Current phase has individual ASHP.
• Secondary heating: Electric immersion in cylinder.
• Hot water storage: Some properties have hot water cylinders and some have thermal stores.
• Space heating: Wet system retained, room thermostat and TRV radiators.
• Ventilation: Aereco demand controlled ventilation.
• Monitoring: Core Controls monitoring of communal energy centre.  Billing and metering carried out by Emergent. Carnego system used for individual heating systems, which was developed to meet the Energiesprong monitoring and control specification.

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The impact – warmer, more efficient homes where people love to live

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Following the pilot phase, additional funding was secured through Interreg ‘E=0’ and ERDF ‘DREEM’ to continue developing the Energiesprong concept in Nottingham City Homes properties across the city.

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A range of suppliers and approaches have been tested through the project, including different ways of manufacturing facades, resulting in Melius Homes Ltd developing their own manufacturing centre in Nottingham.  

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Three different M&E approaches have also been trialled, including a full communal energy system with private wire electricity and communal heating, communal ground source with individual heat pumps and batteries, and in the current scheme, individual air source heat pumps with battery storage.

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“Because these are old buildings… they were hard to keep warm. Now it is easier. One of my kids is autistic and he’s happy as well because he loves the warm. When [friends and family] ask me about my bill they wish the council did their houses as well!” Huseyin Sahin is a resident from the latest phase. He featured on BBC Radio 4's 39 ways to save the planet.

The third phase of homes is in progress (October 2021). A recent survey found that all tenants said they were comfortable or very comfortable in their new homes.