Pioneering Net Zero Retrofit Pilot

Our pioneering Net Zero Retrofit Pilot for Cambridge City Council has started on site.

Axis is delivering the project as main contractor. We will upgrade fifty 1930’s council homes on Ross Street and Coldham’s Grove, significantly enhancing resident wellbeing by creating comfortable and healthy homes that are affordable to heat.

Evaluation of the project delivery and post-completion monitoring will inform the development of future upgrade works to further homes across Cambridge, supporting the Council’s goal to be net zero carbon by 2030.

50 households have volunteered to take part in the pilot – residents remain in their homes throughout the works.

Regular engagement with residents throughout the development, design and procurement of the project has been key to communicating the benefits and securing trust in the process.

Gaining a thorough understanding of the existing performance of the poorly insulated 1930s’ solid wall homes was a key first step to determine the most appropriate upgrade measures. Investigations included resident surveys, energy bill analysis, air tightness testing and heat transfer co-efficient monitoring. Temperature and humidity profiling was also undertaken to assess the critical issue of condensation and mould risk, which is a real concern for residents. Similar monitoring will be undertaken post-completion.

The design brief was to reach a net zero operational energy standard in as many homes as possible, balancing the electricity needed for heating and hot water with electricity generated onsite by photovoltaic panels. The rigorous design process, led by ECD Architects, followed the Passivhaus EnerPHit approach, recognised for efficacy at design and construction stage, and involved extensive and iterative energy modelling in the Passivhaus Planning Package.

Minimising heating demand is key to the EnerPHit approach, and the modelling shows that the final design is close to meeting the EnerPHit heating demand target of <25kWh/m²a. The proposed measures to reduce heating demand include external wall insulation, cavity wall insulation, roof insulation, floor insulation, triple-glazed windows, new doors, airtightness improvements and mechanical ventilation with heat recovery. The heating will be decarbonised by replacing gas boilers with efficient electric powered air source heat pumps and phase-change hot water storage units, which will be powered by roof mounted photovoltaic panels.

“Our qualified (PAS 2035) team will be conducting the deep retrofit works to improve 50 homes on behalf of our client Cambridge City Council and their residents. Because the homes are fully-occupied whilst we conduct the works, and because it is a Pilot scheme, we have created a Resident Website which will serve as a central hub for updates, ensuring residents stay informed and engaged. And our on-site Resident Liaison Officer will support residents throughout the works, arranging further meetings and creating news updates to address residents’ questions and keep them fully informed,” said Stephen Hardy, Axis Divisional Manager and Project Manager