Mercier and Thom Ltd

Ferndale Rise

Impact A carbon-positive home that absorbs more CO₂ than it emits during operation Energy Performance Certificate (EPC) improved from D to A in a 1930s semi-detached property Performance aligned with Passive House standards achieved through retrofit rather than rebuilding A national demonstrator project spearheaded by Cambridge Building Society A data-driven retrofit blueprint for the UK’s ageing housing stock This is not merely a prototype; it is a genuine family home and a model that can be replicated. The challenge The UK is home to 29 million residences needing upgrades by 2050 to meet Net Zero targets. Most of these homes were constructed long before energy efficiency standards were implemented. Ferndale Rise epitomises this challenge: a typical 1930s property, actively used, with no shortcuts available through new builds. The goal was clear: to demonstrate that a deep retrofit could achieve outstanding performance in real-world conditions, not just on paper. Mercier and Thom’s role Mercier and Thom was engaged as the energy efficiency and building compliance expert, tasked with ensuring that the ambitious vision translated into credible, measurable performance. Our contribution went beyond superficial changes. We provided the technical expertise that guided the retrofit strategy, which included: Comprehensive energy assessments and performance modelling for the entire building A strategy for EPC uplift from baseline conditions to an A-rated result A fabric-first approach to minimise demand before adding technology Assurance of compliance to ensure that outcomes were robust, audit-able and authentic The key difference brought by Mercier and Thom was a discerning judgment. We evaluated the building as a cohesive system, considering fabric, airtightness, ventilation and energy generation, ensuring that every intervention worked synergistically rather than in isolation. This approach is why Mercier and Thom was entrusted with a nationally recognised demonstrator project. What changed and why it matters The retrofit significantly transformed the home's performance: Heat loss was substantially minimised Airtightness and ventilation were optimised for comfort and health Low-carbon heating and on-site energy generation were accurately sized to meet demand This effort was not about merely adding technology; it was focused on ensuring the building operates efficiently. The result is a home that consistently provides comfort, efficiency and resilience, not just under optimal conditions. Why this project stands out Ferndale Rise is not a one-time showcase or a ‘perfect’ house; it is intentionally ordinary and this is its strength. No one-size-fits-all solutions No dependence on rebuilding or replacement No performance claims without supporting evidence Instead, it illustrates how well-informed, property-specific decisions, guided by specialised expertise, can yield remarkable results across the UK’s existing housing stock. Ongoing value As the property becomes occupied, it will serve as a living case study, with continuous monitoring of: Indoor temperature and comfort levels Air quality Energy consumption On-site energy generation This data will inform future retrofit projects, policy discussions and homeowner decision-making, extending the impact well beyond a single address. Why Mercier and Thom Ferndale Rise encapsulates what Mercier & Thom excels at. We assist institutions in transitioning from ambition to action. We ensure buildings perform as integrated systems rather than mere collections of parts. This is the result of effective retrofit practices combined with the right expertise.