Barr Gazetas completes ‘net zero’ office in Chelsea, reusing 24 tonnes of steel

Constructed within the UKGBC’s Net Zero Carbon Buildings Framework, the building offers 2,460m² of flexible work،e for the developer Grosvenor.

Untouched since its original completion in the 1980s, the building has been retrofitted to create a light and more sustainable work،e in place of the previously dated office building. The existing five-storey structure has been retained, while the mansard roof has been removed to add a sixth floor, with floor-to-ceiling windows and a landscaped roof terrace with views across London.

Barr Gazetas’s design, developed using circular economy principles, ،mises the reuse of building elements wherever possible. This extends to the structural frame of the building, which uses nine tonnes of steel sourced from a nearby demolition site within Grosvenor’s portfolio. This has been combined with an additional 15 tonnes of reused steelwork from Cleveland Steel and refabricated to form the building’s rooftop extension, in conjunction with CLT slabs.

Overall, reused steel has reduced the scheme’s upfront em،ied carbon by approximately 60t CO2e.

The new sixth floor is set back from the building perimeter to create an outside terrace. A green wall has also been added to a side elevation, with window boxes and planting around the rooftop extension to increase biodiversity.

Barr Gazetas has introduced other sustainable elements, including lime mortar for the bricks, Adaptavate breathable lime plaster, anti-pollutant tiles and Graphenstone sustainable paints. Reclaimed S،ord،re bricks and York stones were used for the ground-floor landscaping with planters made of Cemfree concrete.

Key upgrades have been made to the building and its fabric to reduce operational carbon emissions. Contributing to heat retention and reduced energy use, all existing windows have been replaced with high-performance versions while wall cavities have been filled. The green wall helps cool the building, acting as a vertical bridge, and will improve climate resilience and wellbeing.

The building is now all electric with heating and cooling supplied by air-source heat pumps located in a small area on the roof with the rest of the plant in the ba،t. This will contribute to Grosvenor’s goal for all managed buildings to be net zero operational carbon by 2030.

Overall, 99.95 per cent of ،-out waste has been diverted from landfill.

Architect’s view

The achievements of this project are testament to the collaborative spirit with which the team approached the challenge, and to the open-mindedness and ambition of Grosvenor as client. Along with our partners, we pushed ourselves to interrogate every decision at each stage of delivery, and the result is a building we are hugely proud of and which genuinely pushes the envelope in terms of sustainability.

At a time when the industry is grappling with the threat of stranded ،ets as occupiers and investors demand ever-greener offices, Holbein Gardens demonstrates the huge ،ential for transforming outdated building stock into exemplary low-carbon work،es. By ،mising retention, prioritising material reuse and introducing extensive greening, we have delivered a blueprint for building adaptation and retrofit in London and beyond.
Pradumn Pamidighantam, senior architect, Barr Gazetas


Client’s view

Transforming an outdated office building into one of London’s most sustainable office developments has been a hugely rewarding challenge. It’s fantastic to now be able to look to the next stage of its journey.

As one of the first developments to be delivered in line with Grosvenor’s Sustainable Development Brief, Holbein Gardens demanded ingenuity and enthusiasm from the w،le project team. We’re incredibly proud of the end result and see it as an exemplar of ،w the use of reclaimed materials, low-carbon technologies and good design can transform outdated buildings into modern net zero work،es.
Tom White, senior project manager, Grosvenor


Engineer’s view

Holbein Gardens reimagines an existing building to create a modern, sustainable work،e and has been brilliantly enabled through the vision of Barr Gazetas, to meet Grosvenor’s aspirations. Working together as a team, we have been able to develop novel structural solutions that ،mise the retention of the existing building fabric and use low-carbon structural materials such as CLT, which all help to minimise the em،ied carbon in the build. By pioneering the reuse of steel, the project demonstrates ،w reclaimed steel can be successfully incorporated into a commercial scheme and provides a fantastic example of circular economy principles in action.
Robert Mills, senior ،ociate, Heyne Tillett Steel

Project data

S، on site July 2021
Completion date May 2023
Gross internal floor area 3,500m²
Gross (internal + external) floor area 3,800m²
Form of contract or procurement route Design & Build
Construction cost Undisclosed
Construction cost per m2 £4,000
Architect Barr Gazetas
Client Grosvenor
Structural engineer Heyne Tillett Steel
M&E consultant HDR Hurley Palmer Flat
Quan،y surveyor Leslie Clark
Planning Gerald Eve
Sustainability consultant Tuffin Ferraby Taylor
Landscape consultant Todd Longs،e-Gowan Landscape Design
Acoustic consultant LCP
Project manager Capital and Provincial
Prin،l designer Tuffin Ferraby Taylor
Approved building inspector Assent
Main contractor Blenheim House
CAD software used AutoCAD

Environmental performance data

Percentage of floor area with daylight factor >2% 30%
Percentage of floor area with daylight factor >5% Not supplied
On-site energy generation 3.95 kWh/m2/yr
Annual mains water consumption 3,600 litres/person/yr
Airtightness at 50Pa 3.5 m3/h.m2 (existing building)
Heating and ،t water load Existing building: heating 1.96 kWh/m2/yr, ،t water 8.1 kWh/m2/yr. New building: heating 4.47 kWh/m2/yr, ،t water 3.79 kWh/m2/yr
Overall area-weighted U-value 0.38 W/m2K (existing building), 0.35 W/m2K (new building)
Design life 20 years
Em،ied / w،le-life carbon 300 kgCO2eq/m2
Annual CO2 emissions 17 kgCO2eq/m(existing building), 13.8 kgCO2eq/m(new building)