Dial P for Passivhaus as Telephone Exchange Becomes Ultra-Green Offices

Architype retrofits sustainable offices for a sustainability organization in Cambridge.

Exterior of building before renovation
Exterior of building before renovation.

Soren Kristensen

Ninety years ago, this telephone exchange building (pictured above) in Cambridge, U.K. was probably state-of-the-art, cutting-edge technology, connecting the city and the University of Cambridge to the world. It's fitting that it is now going to be renovated into the state-of-the-art headquarters for the Cambridge Institute for Sustainability Leadership (CISL), "a building which will set new standards for low energy use, carbon emissions, and impact on natural resources as well as user experience and wellbeing measured against multiple benchmarks."

It's called The Entopia Building, a word I recalled from architecture school, coined by the late architect and planner Constantinos Doxiadis; he is quoted on his website:

"What human beings need is not utopia ('no place') but entopia ('in place') a real city which they can build, a place which satisfies the dreamer and is acceptable to the scientist, a place where the projections of the artist and the builder merge."

This seems fitting for the building that will serve as an "ultra-low carbon sustainability hub." The project is being designed by Architype, who were also architects for the Enterprise Centre, which I said might be the world's greenest building, but they didn't just phone this one in– the Entopia Building may well be one of the world's greenest retrofits. Wendy Bishop, a Passivhaus designer at Architype, describes the project:

“The Entopia Building aims to show building owners what can be achieved with a clear focus on cutting operational, embodied and whole life carbon in existing buildings, while creating beautiful and healthy places to work. The project balances the technical demands of meeting the EnerPHit standard with the sensitivities of dealing with a building in a conservation area. Focussing on internal finishes and using bio-based materials that met the multiple certification requirements, as well as using Architype’s pioneering ECCOlab embodied cost and carbon software, we were able to radically reduce embodied carbon and enhance air quality."
Office interior


Architype is a leader in dealing with embodied carbon, avoiding the upfront carbon emissions that come from making materials like steel and concrete, which is why the rendering appears to show a cork ceiling. Some other sustainability benchmarks:

  • The deep green retrofit is projected to result in an 80% saving in whole-life carbon emissions (over 10,000 kg CO2e), compared to a standard office refurbishment.
  • The retrofit will be carried out according to EnerPHit, the Passivhaus standard for refurbishment and one of the most stringent standards for energy retrofits. It will deliver 75% lower heating demand in comparison to an average office building, and airtightness at more than five times that required by building regulations.

And one that I am not so sure about, given that LED lighting technology is getting better every day:

  • The project is one of the first to reuse lighting from another building refurbishment, re-testing and re-warrantying more than 350 LED lights that were then reinstalled in The Entopia Building.

Sustainability advisor for the University, Alexander Reeve, makes the point that Passivhaus fans keep pounding away at, which is to work the demand side. Then you don't need a lot of high-tech or hydrogen as Reeve notes, "as we refine our strategy to eliminate fossil natural gas as a fuel for our many older buildings. It demonstrates that there is a way to transition to low carbon heating whilst conserving Cambridge’s outstanding built heritage."

"Through the project, we have been able to demonstrate the viability of measures such as internal wall insulation and triple glazing which have significantly reduced the size of the air source heat pump installation and avoided the need to upgrade electrical substation capacity. This means the only significant external alterations are the glazing and a solar power photovoltaic array on the roof."
Exterior of existing building
Exterior of existing building.

Soren Kristensen

The glazing presents an interesting challenge. Architype describes the windows as "neo-Georgian sliding sashes with thick frames. Unlike traditional elegant Georgian windows, the current windows appear heavy and impact on daylighting within the building." The building itself is what cartoonist and architectural historian Osbert Lancaster described in 1938 as "Banker's Georgian."

"The architects who were favoured had, as a rule, rather less understanding of the nature and practice of eighteenth-century architecture than the bankers who employed them... One of the most popular of our modern styles... apart from a suspicious newness, the almost invariable feature by which it can easily be distinguished from the genuine article is the high-pitched bogus-Mansard roof."

I raise this because I usually do a spirited defense of fixing historic windows as key to the character of a building, only to have architect Bronwyn Barry defenestrate me with the statement "anyone who is 'energetic' enough to restore old windows in an updated building should also be required to restore the knob and tube wiring and the rotary phones," a particularly appropriate comment for this not exactly classic telephone exchange building.

Architype Window Study


In this case, the architects have chosen to put the windows deep in the building, "beyond the depth of the existing wall to allow the frames to overlap the opening to conceal the window frames from the outside. This maximizes daylighting within the building as well as giving a slick, contemporary appearance, differentiating the new windows from the existing building fabric." It also puts them back where the insulation is, which is technically where they want to be. But I worry that they may end up looking like no windows at all, just deep dark holes; this will be interesting.

Ground Floor


Renovations are often more difficult than designing new buildings, but if one is serious about reducing upfront carbon emissions, you should fix what you've got instead of building new. This one will be fascinating to watch, aiming for such a high standard. Final words from James Hepburn of BDP who is working on the interior design, and has a version of one of our favorite lines:

"The Entopia Building is set to be the most significant project of its type in the country – proving that the most sustainable building is one that already exists."