Exemplar Sustainable Building Awards: Retrofit finalist: Entopia Building

Retrofit finalist in the 2025 Exemplar Sustainable Building Awards. The Entopia Building in Cambridge transformed a 1930s telephone exchange into a cutting-edge headquarters for the University of Cambridge Institute for Sustainability Leadership (CISL). Transforming outdated infrastructure into one of the UK’s most energy-efficient offices, it achieves EnerPHit, BREEAM Outstanding, and targets WELL Gold. The building now operates on just 15% of its original energy demand, showcasing a remarkable 85% reduction.

Contemporary, vibrant and collaborative office spaces - Entopia demonstrates what can be achieved within a typical office refurbishment budget with a clear focus on cutting carbon, while creating a healthy workplace. The transformation cut operational energy demand ,reaching an EUI of just 52 kWh/m²/yr—well below industry targets. Bio-based materials account for 35% by mass and almost 50% by volume of new materials used and the extensive reuse of furniture, fittings and finishes reflects a strong commitment to circular economy principles. This includes over 5,000 items diverted from landfill and reused, saving around 80,000 kgCO₂e in emissions.

Future flexibility was an underlying objective and the project adopts a loose-fit and open plan approach that lends itself to future modification and reconfiguration. This is facilitated by infrastructure distribution through the raised access floors and internal partitions, which are non-loadbearing and can be easily adapted to reflect changing future needs.

What makes Entopia uniquely impactful is its combination of technical excellence and accessible, scalable solutions. From its use of off-the-shelf products and refurbished materials to a design strategy accommodating future flexibility, the building demonstrates how retrofit can meet net zero carbon standards decades ahead of schedule. Future climate models were taken into consideration to ensure that the building will continue to perform and be comfortable to occupy over its 100-year design life.

Key Stats

Certifications: EnerPHit Classic (July 2022), BREEAM Outstanding (March 2025), WELL Gold (targeted)

Date Occupied: September 2022

Treated Floor Area (TFA): 2,573 m²

Gross Internal Area (GIA): 2,939 m²

Construction Cost: £3,417/m²

Annual Running Costs: £11.67/m²

Heat Source: ASHP (integrated into central air handling unit) and supplemented by local electric radiators. Local VRF fan coil system for high occupant density spaces.

Overall Energy Demand: 52 kWh/m²/yr

Embodied Carbon:

130 kgCO₂e/m² (upfront, A1–A5 excl. sequestration)
439 kgCO₂e/m² (whole life, incl. FF&E)

Construction: Retrofit of existing concrete structure, solid masonry walls and tiled pitched roofs with 35% by mass and almost 50% by volume of bio-based materials.