Unlocking the potential of existing buildings
EnerPhit retrofit is one of the most effective ways to cut carbon, reduce bills, and transform comfort. Across Oxfordshire, the Cotswolds, the Chilterns, London and throughout the UK, many homes and workplaces were built long before today’s performance expectations. They are often air-leaky, expensive to run, and inconsistent in comfort.
The EnerPhit standard, developed by the Passivhaus Institute, provides the rigorous framework for deep retrofit. It applies the lessons of Passivhaus design to existing buildings, upgrading fabric and systems to create places that are efficient, resilient, and future-ready. At Gresford Architects, we combine technical rigour with design sensitivity, helping clients reimagine their properties as low-energy, healthy and beautiful spaces.
EnerPhit is a fabric-first, deep-retrofit approach. Using the Passivhaus Planning Package (PHPP), we model each project to predict performance before a single strip-out begins. The result is homes that feel consistently warm in winter, cool in summer, and full of fresh air — while using up to 80% less energy.
What is EnerPhit?
EnerPhit is the globally recognised retrofit standard from the Passivhaus Institute. It sets exacting targets for insulation, airtightness, thermal-bridge minimisation, ventilation, and energy demand — all tailored to the realities of existing buildings.
Typical EnerPhit performance targets include:
- Space-heating demand ≈ 25 kWh/m²·yr (vs ~15 for new-build Passivhaus)
- Airtightness n₅₀ ≤ ~1.0 h⁻¹ @50Pa, verified by blower-door testing
- Thermal-bridge free detailing (Ψ-values minimised)
- High-performance MVHR (mechanical ventilation with heat recovery)
Where phasing is appropriate, we can pursue EnerPhit Step-by-Step certification, supported by an EnerPhit Retrofit Plan (ERP). This allows upgrades to be sequenced sensibly over time without compromising the overall outcome.
Our approach to EnerPhit retrofits
At Gresford Architects, we see retrofit as an act of respect — for history, for resources, and for people.
Our six-step EnerPhit process:
Feasibility → PHPP modelling → Detailed design & moisture analysis → Site QA & airtightness tests → MVHR commissioning → Post-occupancy evaluation (POE).
Our director Tom Gresford has personal experience of EnerPhit: he and his partner retrofitted their own family home, The Old Orchard, to EnerPhit standards. This hands-on knowledge ensures our approach combines technical mastery with lived insight.
A modern wooden house with large windows and a sloped roof, surrounded by a lush garden and trees, under a partly cloudy sky; architecture by Gresford Architects.
The Old Orchard — the deep retrofit of a 1930s detached house, achieving EnerPhit certification with external wall insulation, airtightness strategy, and MVHR — delivering 80% energy savings and exceptional comfort.
An abstract composition with a checkered yellow and green background, large black text reading '3:2 aspect', architecture by Gresford Architects.
Emmington? – A Victorian terrace where period charm meets cutting-edge performance: internal insulation, triple glazing, and smart ventilation raise the home to modern standards without compromise.
Why choose Gresford Architects for EnerPhit?
- Proven expertise: From Oxford townhouses to Cotswold farmhouses, we have delivered EnerPhit-aligned retrofits in diverse contexts.
- Award-winning practice: Winners of the RIBA East Award (2018) for The Deerings Passivhaus, with projects featured by Grand Designs Magazine, Dezeen, The Modern House and The Spaces.
- First-hand knowledge: Tom’s own EnerPhit-level retrofit, The Old Orchard, has been profiled internationally.
- Professional standing: A RIBA Chartered Practice, Green Register accredited, and members of the Passivhaus Trust and AECB.
- Heritage sensitivity: With ties to the Society for the Protection of Ancient Buildings (SPAB), we balance conservation with performance.
- Client-centred ethos: We measure outcomes as well as aesthetics, providing airtightness certificates, MVHR commissioning reports and post-occupancy reviews.
With Gresford Architects, an EnerPhit retrofit is not just an upgrade — it is a transformation into a healthier, more efficient and more resilient home.
Ready to transform your home?
If you are considering a deep retrofit and want the benefits of EnerPhit — lower energy use, healthier air, and a home prepared for the future — let’s talk.
