By Carole Charter, Chief Commercial Officer, Cambridge Building Society

What does leadership look like for mutuals? It’s not just about competitive products, community or digital innovation - it’s about how we can tackle one of the greatest housing challenges of our time: decarbonising 29 million UK homes before 2050.

This is not a distant problem. It’s here now. In Cambridgeshire alone, 250,000 homes need energy efficiency upgrades. If mutuals don’t step up, who  will? Our sector was built on community resilience, problem-solving and long-term thinking. 

So, we decided to step up to the challenge. Our Ferndale project is a deep retrofit of a typical 1930s  semi-detached home that we’ve transformed into a carbon-positive living case study, improving the EPC rating from D to an A and delivering Passive House standards for air tightness. 

Ferndale is proof that ambition and innovation can transform the ordinary into the extraordinary. We’ve installed renewable technologies - from an air source heat pump to solar panels and a rainwater  harvesting system. It is now an old home fit for the future, removing more carbon dioxide than it emits.

This matters because most UK homes are not new builds. If we fail to take up the retrofit challenge, we will fail to meet net zero targets. Ferndale demonstrates that deep retrofit is achievable when approached with creativity and collaboration with contractors.

Ferndale is not just a house - it’s a living educational resource. We recognised many homeowners want to make sustainable upgrades but don’t know where to start. Over 15 months, the team collaborated with architects, energy experts and tradespeople to modernise the property using a blend of both traditional and innovative techniques.  



We now plan to share real-world data on energy performance, air quality, and cost savings to  demonstrate what older homes can achieve, not just in performance but in inspiring others to act. Because knowledge is the biggest barrier to action. Lenders, homeowners and policymakers need clarity on what it costs and the benefits it delivers.

By investing in this project and the educational programme we’re delivering - including tours of the property for our members and community - we’re helping individuals make informed choices. Building societies can all play a pivotal role in closing the knowledge gap, influencing regulation, and driving consumer confidence in sustainable solutions.

For 175 years, The Cambridge has responded to the housing challenges of each generation. Today,  climate change is one defining challenge. Mutuals are uniquely positioned to lead because our purpose is aligned with long-term community wellbeing.

Ferndale signals to members, regulators, and peers that building societies are not passive observers in the sustainability debate - we are active innovators. The retrofit revolution requires leadership, collaboration and investment. Mutuals can:

• Champion education: Share insights, demystify and empower homeowners.
• Influence policy: Advocate for incentives and schemes that make retrofit viable.
• Innovate with lending: Develop products that support sustainable home improvements.
• Collaborate: Work with traders, providers and government to scale solutions.

Ferndale is a game changer - a retrofit that delivers on comfort, carbon, and community. But this project should be a starting point, not the end. The question is not whether building societies should lead - it’s whether we can afford not to.

Key upgrades include:

• Two types of extension rear timber frame and side brick-built extension
• Comprehensive insulation internal, external, cavity, roof and floor
• Airtightness measures using innovative liquid membrane
• Air source heat pump
• A combination of underfloor and radiator heating throughout the property
• Mechanical ventilation system with heat recovery
• 12-panel solar PV system including modular battery and EV charger
• Triple-glazed windows and doors
• Rainwater harvesting system

 For more information about the retrofit visit www.cambridgebs.co.uk/greener-living

This article was first published in Society Matters magazine