Upgrading social housing in Nottingham through Energiesprong deep retrofit. Transforming 63 occupied council properties into desirable, warm, affordable homes, tackling climate change and fuel poverty. Photos by Tracey Whitefoot

Energiesprong

Energiesprong is a form of deep home retrofit that focuses on a house’s main components, such as wall and roof insulation, windows, air quality, and smart heat recovery. Previously, the options to enhance your home were to address all these issues at the same time or to create a plan to tackle each issue individually. With Energiesprong, all the problems can be tackled simultaneously, and the main goal is to increase the home’s energy efficiency and occupants’ comfort.

Energiesprong brings existing housing up to 2050 standards using an innovative, whole-life approach to finance. The cost of the works is designed to be equal to the expected savings in maintenance and energy over a 30-year period. It is outcome-based, offering guarantees for both landlord and tenant.

Key Innovations of Nottingham social housing upgrade

– Pioneered the Dutch Energiesprong approach in the UK. • Retrofit is undertaken over 12 days while people live in their homes.

– The Contractor assures performance through monitoring after the project is complete.

– Advanced MMC factory established in Nottingham, creating local employment and training opportunities.

Works programme

The scheme comprises 1960s nontraditional concrete cross-wall homes, including terraces of three-storey houses, low-rise flats, and bungalows in Sneinton on the edge of the city centre. While the homes are well located and had an established community, they were cold and draughty with an inefficient design, particularly the houses with an unheated garage under the living room and an undercroft below the kitchen.

The solution was a tenant-focused, highly efficient whole house retrofit delivering super insulated, low maintenance near ‘net zero operational energy’ homes. The retrofit has also transformed the neighbourhoods with brighter finishes and increased passive surveillance from converted garages and first-floor Juliet balconies to some houses.

The design team, led by Studio Partington, involved residents in developing the design brief during the competitive dialogue tender process. The community came together to establish a ‘wish list’ and choose the colour of their own window surrounds. The Contractor was able to include small items which make a big difference to residents’ lives, such as light tubes making stairs brighter, outside taps for watering, and doorbells.

Nick Murphy, Chief Executive, Nottingham City Homes, commented: “While we’re delighted to be part of a UK-first pilot programme, it’s more important to us that we’re creating warmer, more energy efficient homes, which are cheaper to run for residents. As an added bonus, the improvements will greatly enhance the look and feel of the area.”

Delivered benefits

• Fabric first: full external insulation, double glazing, improved air tightness, reduced thermal bridging.
• Energy supplied efficiently using heat pumps (gas removed) and solar panels to minimise grid-imported electricity, getting down to around 1,500kWh/year (per home).
• Measured performance shows average space heating consumption of 58 kWh/ m2/yr (within 2% of target value).
• Measured solar PV production is, on average, 35 kWh/m2/yr (per home).
• All surveyed tenants said they were comfortable or very comfortable in their retrofitted homes (October 2021). • Social value up to £4,500 a year per home (HACT).
• Total embodied carbon was calculated as 26t CO2e compared with circa 120t CO2e for demolition and rebuild.

Energiesprong sustainability

2050 Homes Nottingham pioneered the Dutch Energiesprong revolutionary standard and funding approach for whole house retrofit. The initial 10-home pilot project was the first in the UK to pilot net-zero Energiesprong retrofits.

The Solution Provider, Melius Homes, and the Architect, Studio Partington, were procured to deliver the Energiesprong performance outcome, including 1500kwh net import, a maximum cost and guaranteed comfort for tenants. The innovative competitive dialogue tender process evaluated whole life cost and design quality and included tenant representatives in decision making.

– External walls: Prefabricated timber frame panels, complete with 200mm of mineral wool insulation, windows, and a durable board finish, installed on insulated foundations.

– Roof: Refurbished existing roofs/ new cassette roofs (Phase 1 only) with in-roof solar.

– Windows: Double-glazed high performance.

– Heating power: Communal energy system in pilot with GSHP. GSHP with individual heat pumps in Phase 1. Phase 2 has individual air source heat pumps.

– Secondary heating: Electric immersion in cylinder.

– Hot water storage: Some have 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.

Near net-zero homes

The Energiesprong standard focuses on creating desirable, warm, affordable, nearnet- zero homes in which people want to live. There are two important innovations. Firstly, people carry on living in their homes during the retrofit.

Secondly, it is an assured performance scheme. The Solution Provider (the Contractor) signs a contract to meet the energy and comfort targets. The only way this can be achieved is by monitoring every home after completing the project.

The Energiesprong approach is designed to unlock zero carbon retrofit at scale, paid for by energy and maintenance savings and delivered by a new British offsite manufacturing industry.

Sustainable construction supply chain innovation

The pilot tested different façade panel suppliers and found a supply chain shortage (panels were not full-width and did not include windows). This resulted in Melius Homes establishing their own advanced MMC Category 2 factory in Nottingham for Phases 1 and 2, creating local employment and training opportunities.

Energy measures

For the pilot (seven terraced homes, 2.5- to three-storeys high, and three bungalows), two ground-source heat pumps (GSHPs), a battery and two thermal stores were installed at the end of the terrace in a 20ft shipping container, linked to the homes by a distribution system.

One GSHP produces water at 55°C and 60°C for domestic hot water, and the other is optimised for 35-40°C. The extra insulation (prefabricated panels, with 200mm of insulation, were installed on the front and rear elevations of each home, on insulated foundations) meant the heating requirements fell considerably, and Melius could use the existing radiators with water temperatures at circa 40°C.

Lessons learned

As the project has developed lessons have been learned and different M&E systems trialled. Although the full communal energy system (with private wire electricity and communal heating) is helpful to offset diversity by balancing energy use and energy storage across a group of homes. It proved costly and difficult to retrofit the energy centre and distribution system in an urban setting.

Later phases have tested different M&E approaches, moving towards self-contained individual air source heat pumps with battery storage for each home.

Whole-life carbon assessment

A life cycle assessment has been completed to calculate the embodied emissions associated with the works undertaken, compared with the emissions associated with demolition and rebuilding. The total embodied carbon was calculated as 26t CO2e compared with circa 120t CO2e for demo and rebuild. The highest embodied carbon element of the works was the supply of solar PV panels, which accounted for 20t CO2e, ie 77%.

While they were well located and had a great community, before the retrofit, these concrete cross-wall council properties were freezing cold, and tenants said external walls felt as though they moved when they leaned on them.

For social tenants, the high energy costs to adequately heat their poorly insulated homes made them hard to heat. Some residents did not turn on their heating, while others limited it to the living room.

The Client, Nottingham City Homes (NCH), earmarked the properties for improvement as they were inefficient, with non-traditional post-war construction, and were a repeated archetype across the city. NCH had the option of demolishing and rebuilding them for £120,000 per house or finding a way of refurbishing them at a reasonable cost. This is where the Energiesprong revolutionary standard and funding approach for whole house retrofit came in.

The ‘Energiesprong’ energy leap

Based on Energiesprong (meaning ‘energy leap’) principles, the business case brings forward energy and maintenance savings for the next 30 years to create an investment envelope. This finance is used to create a near-net zero home, which is attractive, comfortable, and affordable for residents.

Design performance modelling (to meet the detailed Energiesprong performance specification) and monitoring (of energy use, temperature, and relative humidity) in every retrofitted home ensures tenants pay no more than before for a comfortable home.

A deep retrofit, extending the dwellings’ lives by 60 years, avoids considerable construction waste and embodied carbon. The total embodied carbon associated with the retrofit works undertaken was calculated as 26t CO2e compared with circa 120t CO2e for demolition and rebuild.

People carry on living in their homes during the works, which typically takes 12 days. Demolishing and rebuilding would have increased the project cost and broken up the community, necessitating them to move apart. Measurement by HACT UK social value bank shows social value of up to £4,500 a year per retrofitted home.

One of the innovations that underpins the model is that the Solution Provider signs a performance guarantee, ensuring that the in-use energy use and generation are in line with the approved design. Therefore, the design of solutions and selection of components were considered in detail within the energy modelling, including factors to account for the actual performance expected rather than manufacturers’ stated performances. Additionally, the fabrication and construction details were carefully developed to ensure site works could be completed without compromising the intended airtightness and thermal continuity.

The intent and the outcome were to eliminate the ‘Performance Gap’. Metering and monitoring were included as part of the solution to enable actual performance to be measured and monitored.

A community transformed

The retrofit has transformed the neighbourhood with light finishes, new on-street entrances and passive surveillance from Juliet balconies to some houses (righting some wrongs of the original layout). Bright colours around windows, chosen by the residents, give each terrace its own identity and deliberately make a citywide statement that the area has changed and is embracing renewal, energy efficiency and healthy living.

Case study courtesy of Energiesprong UK Ltd, https://www.energiesprong.uk

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