The brave new world of low carbon retrofit


A large-scale retrofit project to bring energy efficiency of social housing across Northumberland and County Durham up to a C rating saw a housing association deploying robots to upgrade homes with minimal disruption. James Parker reports.

The Socal Housing Decarbonisation Fund (SHDF) was launched in October 2021 by the Government, as a key part of its Heat and Buildings Strategy, dedicated to upgrade the efficiency of the most in-need rented social housing across England.

The Government initially announced £160m worth of funding for projects, including heating upgrades, energy efficient doors and windows, and upgraded insulation, to make a significant difference to social housing tenants’ energy bills (estimates putting savings around £170 per year). One of the projects in the first wave (chosen for funding based on a criteria of having EPC ratings of D or lower), is a £2.5m retrofit programme by housing association Karbon Homes. It covers 91 homes in two locations, one delivered in partnership with Northumberland County Council and the other with Durham County Council. 

This is a scheme which tackles housing in differing settings, but both in severe need of low energy retrofit, and by so doing has demonstrated some substantial improvements for residents. Fabric improvements – chiefly insulation – were at the core of the measures which Karbon undertook, including fitting external wall insulation (EWI), as well as cavity, loft and underfloor insulation. However, the latter saw some unusual innovation in the social housing sector, using a robot to install it and thereby minimise disruption to tenants. 

As well as insulation, the project also included re-roofing many of the properties, and adding PV panels to assist in reducing their carbon footprint. PV has been added to help reduce fuel bills and support “grid resilience” for the homes, however the team had to demonstrate that all fabric options had been explored first. The PVCu windows across the schemes still had a considerable life left in them, so replacement was not required.

The scheme comprised a mixture of bungalows and houses with cavity walls, and a variety of heating methods from gas to solid fuel – some even had air source heat pumps. Before the project, the homes’ EPC energy performance ranged from D to F. A number of the properties are in rural locations, and in an area where residents have a 15-20% likelihood of experiencing fuel poverty.


Karbon Homes formed in 2017 as a merger between three north east housing associations, and now owns and manages close to 30,000 homes across the North East and Yorkshire. The overall Karbon Group it belongs to spans beyond further across Yorkshire; as far as Leeds to the west and Hull to the east. The Group also includes 54 North Homes, which formed at the end of 2022 with the merger of two housing associations, Leeds & Yorkshire Housing and existing subsidiary of the Karbon Group, York Housing Association.

Karbon Homes covers a wide range of social housing properties, from those in dense urban areas, to others in very rural communities. One of the organisation’s key aims is to “shape strong and sustainable communities,” and this energy retrofit project is a striking example of that goal in action, by enabling people to have energy resilience for the long term.

As it embarked on the project, Karbon had a big learning curve in terms of not only the right energy efficiency measures to approach, but firstly just to gather a large amount of data on the condition and need of its properties. As Craig Lonsdale, asset and sustainability manager at Karbon Homes told Housebuilder and Developer, “we spent a lot of time analysing all of our homes from an energy perspective.”

David Milburn, head of investment at Karbon Homes explains that the two schemes – at Ouston, an urban location in Chester-le-Street, and a rural street in Otterburn in Northumberland, were “very different.” Despite their differences, both schemes had suffered similar energy efficiency issues, including the failure of the original cavity wall insulation.


The overall driver is that all ‘fuel poor’ social rented homes will need to be EPC rated C or above by 2030, according to law; the Government’s ‘EPCC’ initiative. They discovered they had 7,000 homes that didn’t come up to that standard, so the task was clear. 

It was timely that the Government announced (in 2020) the SHDF funding at a similar juncture, says Lonsdale: “a nice sum of money to treat your worst homes first.” He says that having been through the process to understand which the worst performing homes were, it meant that they could target the “worst first,” he says, adding that the “two streets stood out.” These were D and E rated mid-20th century homes in both locations. Otterburn was off grid, with a combination of LPG and storage heaters, meaning their homes had a lower EPC rating than normal, despite having loft and cavity wall insulation.

Lonsdale adds: “Installing EWI and solar PVs was the only way those properties were going to get the next level of performance for the C rating.” 

As well as better thermal comfort for residents, and improved aesthetics from measures like EWI, the project is hoped to be able to save residents up to 40% on their energy bills. By significantly reducing the homes’ carbon footprint, the housing association has modelled a potential saving of 60 tonnes a year from this first wave of the project alone.


The housing association had to lodge a bid for the funding, which they in turn submit to the Government. But because the two streets were in different local authority areas (Durham CC and Northumberland CC), that meant two separate bids. Karbon’s bid included surveys, measures deemed appropriate per property, and “it was a mixed bag of works,” says Lonsdale. However, they would all receive EWI and a 4 kW solar PV array, which none had previously.

The project team used data modelling software to identify what the most cost-effective route to take each home from an E rating to a C, based on their current state. The software looks at each property in turn, and outputs the costs, projected fuel bill reductions, and further results in terms of “what it looks like on completion.” In addition, as Milburn explains, thermal imaging has exposed “huge gaps” in the previously installed cavity wall insulation, which also had to be addressed.

Milburn says candidly, “there were a lot of companies that went around doing cavity wall insulation for housing associations, and the insulation basically wasn’t fit for purpose. It was put in by incompetent contractors.” The result has been tenants living in properties with condensation and mould in some cases.

There are two contractors involved in delivering the refurbishments; energy company Eon carried out the work at Otterburn, and north-east regeneration specialistsRE:GEN Group at Ouston. The project is progressing to its hoped completion in October, but with the programme taking place largely over the winter, there were some challenges, particularly with the EWI, a wet trade; “you can’t put it on when it’s too cold,” says Lonsdale. In fact, it needs to be above 5 degrees for a 12-hour period for the installation to be effective, and Northumberland winters won’t always cooperate with that requirement.

All the works have been designed to PAS 2035 standards – the national framework standard for energy retrofit. Craig explains that Karbon “relies on its retrofit assessors” to ensure that the installations comply, as well as the contractor itself. As part of the funding arrangement, Karbon provides regular coordinated design updates to the council to demonstrate the “relentless push” towards a C grade EPC, in order to have the staged funding released.

Getting residents to “sign up” was challenging, says David Milburn – but the project team held open days where the residents could meet the contractors, discuss the works and the benefits they would bring, as well as aspects of the programme. He says that although they “could not make promises their gas bills would be halved,” but reducing their expense was the key message.


When it came to which properties would receive which solution, as well as the software’s judgement, there was also an overriding aesthetic consideration, says Lonsdale. “With EWI, you’ve got to do all the properties.” However this meant challenges, as every installation was weather dependent, notwithstanding keeping the planners happy on the precise render colouring, as it was a change from brick to a more uniform colour. The proof in the pudding is that neighbouring private owners who didn’t have their exteriors insulated, were asking the housing association when theirs could be done, reports Milburn.

The project software used gave the team a lot of detailed info in terms of how to treat each property, including the recommended and appropriate product solutions in each home’s case
(for example it won’t suggest triple glazing in a conservation area). This also came down to the exact dimensions of EWI to be installed, for example, which might be constrained based on where a damp proof course was, or if air bricks needed to be left uncovered. The software’s other benefit is providing estimated running costs of the properties, however energy price rises are making this increasingly complicated.

One of the major hurdles for making the PV installations a success was ensuring that the customers contacted their own energy supplier to install the necessary isolator switches in each property – this could not be done by the contractors, and the cost was down to the customers. In addition, the energy suppliers were not all swift in doing these installations; legislation has since changed meaning that a wide range of firms can now install them. The solution arrived at was the customer making the outlay but the housing association reimbursing them quickly, so they can start saving money from renewables quickly. 

Further measures included re-roofing some properties at Ouston, including aesthetically attractive integrated PVs, and adding wall ties where needed to structurally protect them. The Otterburn off-gas scheme had a few more air source heat pumps installed, but some of the properties already had them.


The Chester-le-Street scheme had solid concrete floors, so underfloor insulation wasn’t an option, but the wooden floors at the more rural Otterburn scheme meant it was possible. However, to do it without disrupting tenants – many of whom were older residents in bungalows – meant a very innovative approach was needed. While lifting tenants out of fuel poverty is the most important aspect of the scheme, the most eye-catching is the fact that to make the installation of underfloor insulation possible without the expense and upset of residents having to be decanted, the team called in the help of a robot.

Provided by Q-bot, the remote controlled robot, which moves using tracks, is inserted into the underfloor void through a small hole cut in the floor, and sprays insulation to the underside of the suspended floors – taking around half a day per property. Crucially, the robot then verifies that the work has been done correctly, thereby obviating any chance of a ‘performance gap,’ given that it is operating unseen by human eyes (although visible through the camera).

As well as quickly stopping heat loss through properties’ floors, it also stops draughts, bringing greater comfort all round. According to Karbon, it is a “straightforward, no hassle and cost-effective solution,” despite the apparently futuristic nature of the approach. But moreover, it meant a full fabric insulation was possible in a retrofit scenario in many of the properties (underfloor space permitting), making them ‘net-zero ready’ as the grid continues to decarbonise.


EPCC 2030 is a major challenge, but Karbon Homes and the projects’ stakeholders have taken a large step towards success, at least in these two initial schemes.

Karbon Homes is also pursuing modern methods of construction (MMC) including timber framed houses and full modular builds for its new home programme. With the predictable quality from factory construction, it hopes to produce even better energy performance for its residents. In addition, the housing association is looking to provide percentage estimates to customers on running costs through its software, which will be less prone to being sabotaged by volatile wholesale energy costs, and the vagaries of residents’ different tariffs
and contracts.

In April 2023, Karbon Homes was given funding from the Government’s Social Housing Decarbonisation Fund Wave 2.1, a grant of over £580,000 to upgrade more homes. Added to the existing money for the retrofits already underway, Karbon is putting £3.6m into improving the energy efficiency of 218 of the most energy-challenged homes in Northumberland and County Durham over the next two years. 

This next project contributes towards a wider £80m retrofit investment across the North East and Yorkshire, delivered by a consortium of 18 housing associations, councils and local authority-owned organisations (ALMOs), and led by the North East and Yorkshire Net Zero Hub. Taken together, the consortium’s projects will see energy efficiency investments made to 5,525 homes across the region, supported by a total of £32.4m pledged by the Department for Energy Security and Net Zero. 

This not only demonstrates the awareness and foresight of the housing association, but how the Government is finally tackling the large-scale retrofit which is essential for the UK to have a chance of getting close to 2050 net zero targets. And with the cost of living crisis still biting hard for many social housing tenants, this innovative project as well others underway by Karbon will provide a huge relief long-term.