Holbein Gardens: Retrofit, Reuse and Net Zero Workplaces

In this Architecture Social conversation (approximately 40 minutes), Stephen Drew speaks with Pradumn Pamidighantam, Senior Architect at Barr Gazetas, about Holbein Gardens: the sustainable retrofit of a 1980s office building off Sloane Square in London. The discussion covers reuse over demolition, the net zero carbon journey, circular economy thinking, smart building technology, and what practices look for when hiring for sustainability-focused work.

Who this is for

Architectural assistants, architects, technologists and students who want a practical, plain-spoken introduction to sustainable retrofit and high-performance workplaces, plus anyone weighing how to build sustainability skills into their career. It is also useful for practice leaders interested in how a collaborative, research-led project comes together.

Learning outcomes

1. You will be able to explain why retrofitting and adapting existing buildings can outperform new build on carbon and value.
2. You will be able to describe how operational and embodied carbon are assessed, and which industry frameworks guide net zero work.
3. You will be able to apply circular economy principles, such as cradle-to-cradle materials and takeback schemes, to specification decisions.
4. You will be able to outline the certifications used on high-performance workplaces, including BREEAM, WELL, NABERS and SmartScore.
5. You will be able to explain how smart building technology and mixed-mode ventilation reduce energy use in occupied offices.
6. You will be able to identify the skills and attitudes practices look for when hiring for sustainability-focused roles.

Retrofit before new build

Barr Gazetas has long worked with existing buildings rather than defaulting to demolition, and that experience has become a core strength. With a large stock of ageing buildings across London and the wider country, the central question is how to upgrade and adapt what already exists while reaching high performance standards. Holbein Gardens started from exactly that brief: a fairly standard 1980s building that could be transformed rather than replaced.

The brief and the client's ambition

The project coincided with the client's new sustainability policy, structured around several themes covering issues such as biodiversity, connections to the community and circular economy. The client set an ambitious net zero operational carbon target for 2030, which shaped the design from the outset. Pradumn notes that almost every major developer is now asking how to hit 2030 and 2050 targets, and that the honest starting point was that not everyone had the answers, so the team had to research and test them together.

Measuring the net zero carbon journey

A recurring theme is that the industry is still settling on consistent ways to measure carbon. Different organisations have used different methods, and a clearer consensus is emerging through guidance from bodies such as the RICS and LETI. Pradumn frames the practical questions simply: what does the existing building do now, what will you do to adapt it, and what is the impact of that, both in materials and in energy. Energy modelling has become a large part of the work, with mechanical and electrical teams effectively building a virtual model of the building to test heating, cooling and electricity demand.

Circular economy and materials

Circular economy thinking ran through the specification. The team selected products with strong end-of-life credentials, including windows carrying a cradle-to-cradle certification and carpet tiles from a supplier that takes the tiles back for recycling. Pradumn highlights a clear shift in supplier attitudes over the last five years, from having to chase environmental credentials to suppliers offering them proactively. He points to the NLA's report on a circular, renewable London as a useful, readable overview for anyone wanting to understand the principles.

Certifications and performance

Holbein Gardens targets a demanding set of standards, including BREEAM Outstanding and WELL Platinum, alongside NABERS for accurate operational energy and SmartScore for building intelligence. Pradumn explains that standards like NABERS depend on real data and sensors, which is pushing more technology into buildings so that performance can actually be measured rather than assumed.

Smart buildings and mixed-mode ventilation

One feature the team is proud of is mixed-mode ventilation. An air quality sensor on the roof measures conditions around Sloane Square, and when the air is good a light on the office floor signals that windows can be opened to save energy. Opening the windows talks to the building management system, which shuts down the air conditioning. It is a simple, human prompt backed by building intelligence, and a good example of technology serving energy reduction and occupant comfort together.

Collaboration as genuine practice

Pradumn is candid that collaboration is often talked about but less often truly practised. On Holbein Gardens it was essential: an engaged client, a strong sustainability consultant, and committed structural and mechanical and electrical engineers worked alongside the architects to research questions none of them could answer alone. He sees this collaborative, problem-solving approach becoming the norm on more projects that aim for a high benchmark.

Careers, attitude and people-centred design

On hiring, Pradumn looks for people who are genuinely engaged in designing buildings that have a positive environmental impact. Awareness of sustainability is increasingly a given, and he was struck by a student who had run a BREEAM assessment on a final project. His wider advice is that software can be learned, but attitude and design awareness matter most. He also stresses designing for people, from passive design and good daylight to biophilia, multi-faith rooms and quiet study spaces, and being able to evidence that thinking in a portfolio.

Inside Barr Gazetas

Founded by Alistair Barr and Tom Gazetas, Barr Gazetas recently marked its 30th anniversary. The practice has grown to around 55 people and brings together architects, interior designers, BREEAM assessors and digital specialists. Its bread and butter is commercial offices, with strengths in retrofit and reuse, and a track record that includes the regeneration of Greenwich Market, the residential conversion of Lewisham Tower House, and One Heddon Street, the Crown Estate's co-working scheme.

Key terms

Retrofit: upgrading and adapting an existing building rather than demolishing and rebuilding. Embodied carbon: the carbon associated with materials and construction. Operational carbon: the carbon from running a building in use. Net zero operational carbon: balancing operational emissions to zero. Circular economy: keeping materials in use and out of waste. Cradle to cradle: products designed so materials can be recovered and reused. Mixed-mode ventilation: combining natural ventilation with mechanical systems. BREEAM, WELL, NABERS, SmartScore: certifications for environmental performance, occupant wellbeing, operational energy and building intelligence. Biophilia: design that connects occupants with nature. Employee Ownership Trust: a structure in which a business is owned on behalf of its employees.

Reflective prompts for your CPD record

1. Think about a building you know well: what could be reused or upgraded rather than demolished, and what would you need to measure to make the case?
2. Where in your current specifications could you ask suppliers for cradle-to-cradle credentials or material takeback schemes?
3. How could you evidence sustainability awareness and people-centred design in your portfolio or your next project?

About the guest

Pradumn Pamidighantam is a Senior Architect at Barr Gazetas, which he joined in 2014. He studied at Liverpool and Nottingham Trent and completed his professional qualification, and has led the practice's team on Holbein Gardens over roughly three years.