Retrofitting History: 1920s Oxford home set to achieve Passivhaus excellence

When faced with a leaky roof and persistent dampness, the homeowners of this charming 1920s Oxford property set out to not just repair but reimagine their home for a more comfortable and energy-efficient future.

1920's Oxford Retrofit - Image credit: eco Design Consultants

What began as a much-needed roof fix quickly evolved into a full-scale retrofit aiming for Passivhaus certification. The moisture-damaged roof, further compromised by outdated spray foam insulation that had fused the tiles together, demanded more than a patch-up—it called for a complete overhaul. Embracing a "fabric first" approach the home's form factor was improved, replacing the projecting bays with flush, triple-glazed windows and removing the chimney and its gable roof to streamline energy performance.

Preserving the home’s historic character was a priority. The renovation team, led by PHT Patron Eco Design Consultants, carefully selected materials that matched the original 1920s architecture, seamlessly blending heritage with modern Passivhaus standards.

1920's Oxford Retrofit - Image credit: eco Design Consultants

In addition to resolving structural problems, the retrofit addressed ongoing damp issues, especially in the northeast corner of the home. An Air Source Heat Pump (ASHP) replaced the old gas boiler, and a Mechanical Ventilation with Heat Recovery (MVHR) system was installed. These enhancements have propelled the project past EnerPHit targets, with full Passivhaus certification now in sight—all while meeting the sustainability goals of the Oxford Local Plan 2036, which champions green retrofitting of existing buildings.

U-values

Roofs

Pitched Roof: 0.105 W/m2K

Flat Roof: 0.114 W/m2K

Dormer Pitched Roof: 0.122 W/m2K

Dormer Flat Roof: 0.147 W/m2K

Walls

Solid Masonry EWI - Below DPC: 0.171 W/m2K

Solid Masonry EWI: 0.146 W/m2K

Dormer Cheek: 0.120 W/m2K

Floors

Utility Solid Floor: 0.086 W/m2K

Kitchen Floor: 0.210 W/m2K

Living Room Solid Floor: 0.085 W/m2K

Rafters at 1920's Oxford Retrofit - Image credit: eco Design Consultants

EWI - 1920's Oxford Retrofit - Image credit: eco Design Consultants

Window Installation - 1920's Oxford Retrofit - Image credit: eco Design Consultants

Building performance

Designed energy performance
Space Heating Demand (≤ 15 kWh/m².a)	15 kWh/m².a
Heating Load (≤ 10 W/m²)	10.9 W/m²
Primary Energy Renewable (PER) Demand (≤ 60 kWh/m².a*)	28.2 kWh/m².a
Primary Energy Renewable Generation	26.4 kWh/m².a

*+/-15 kWh/m².a allowance if offset by energy generation. See Passivhaus criteria.

Want to learn more?

Stay tuned! Discover more about this exciting Passivhaus Retrofit development at the UK Passivhaus Conference 2024. Join us on the 19th of September and hear from the Airtightness consultant Paul Jennings, Jennings Aldas, Principle Contractor Duncan Davison, Husker Build, Client Deborah Henderson and Architect Alan Budden, Eco Design Consultants.