A 1930s telephone exchange in Cambridge, UK, has been retrofitted and converted into a "joyful and welcoming" office building by architecture studios Architype and Eve Waldron Design.

Named Entopia, the building was adapted for Cambridge Institute for Sustainability Leadership (CISL), a part of the School of Technology at the University of Cambridge.

Architype's and Eve Waldron Design's interventions have provided a mix of meeting rooms and flexible work areas for up to 375 people, alongside breakout and event spaces.

While providing a staff base for CISL, these facilities also accommodate The Canopy – a workspace hub aimed at eco-entrepreneurs and small businesses.

CISL's brief for the retrofit required the team to improve the building's energy performance and meet various rigorous energy standards, such as Passivhaus, as well as to minimise material waste and consumption throughout.

Architype led the architectural retrofit, while Eve Waldron Design carried out the interior overhaul in line with these sustainability goals.

"The Cambridge Institute for Sustainability Leadership wrote a very ambitious and challenging brief for the project, which set stringent targets for the building's performance, as well as the overarching aspiration to be an exemplary retrofit that in itself would be an 'educator' and enable leadership and dissemination to others," Architype's Wendy Bishop told Dezeen.

"The brief also required that the project would demonstrate good value for money while challenging conventional norms around building refurbishment. "

The majority of changes that have been made to the building to improve its energy performance are internal or not immediately obvious to passersby.

For example, internal insulation has been added to the building's outer walls, as well as to the thermal bridges, ground floor slab and roof. A large central mechanical ventilation with heat recovery unit has also been introduced to the basement.

Among the energy targets this enabled Architype to meet was EnerPHit Classic – a standard for refurbished buildings based on Passivhaus-oriented requirements. According to the studio, it is currently "the largest certified EnerPHit office in the UK".

Entopia's occupancy is also slightly lower than originally expected due to changes in office working post-pandemic, reducing its operational energy consumption, Architype said.

Some of the more visible changes to the building included windows updated with triple glazing and the removal of a rooftop plant room.

The removal of the plant room created space for a rooftop terrace, sheltered by a steel canopy. This is made from reclaimed steel and supports a series of photovoltaic panels.

Internally, Entopia's original circulation core has been retained, but some internal partitions have been removed in order to reconfigure and modernise the interior, which has been fitted out by Eve Waldron Design.

Eve Waldron Design's interior scheme is shortlisted in the sustainable interior category of the Dezeen Awards 2023.

"Our aim was to transform Entopia from being dark, uncomfortable and poorly performing, into a contemporary, vibrant and collaborative space that highlights innovation in circularity, health and wellbeing," the studio's founder Eve Waldron told Dezeen.

"We wanted to create a joyful and welcoming interior without inserting gratuitous and wasteful decorative finishes. We therefore had to make a strong impact with fewer materials and interventions," Waldron said.

To achieve this, the studio opted for colour blocking in each space. This is done through a combination of paint, graphics, floor lino and joinery.

"Restorative shades of blues and greens with pops of warm orange were used throughout the office areas, while deep yellow and bold graphics in the reception and stairways is to encourage using the stairs over the lift," Waldron said.

Second-hand furniture has also been used to add character to the interiors, including a number of mid-century design classics such as Happy Chairs by Boss Design. According to the studio, these pieces "transcend trends, thus ensuring their own longevity".

Alongside Entopia, other projects shortlisted in the sustainable interiors category of the Dezeen Awards are the Big Beauty store by Nina+Co and the Edit restaurant in London by Elly Ward and Joe Morris.

Elsewhere in Cambridgeshire, Architype created an archive for the Imperial War Museum, which is the most airtight building in the world.

The photography is by Solk Photography unless otherwise stated.