Project Overview

Redevelopment and one storey extension of a 1980s office building off Sloane Square, creating a 25,000 sq ft modern workplace planned to align with the UKGBC’s Net Zero Carbon Buildings: A Framework Definition.

Climate change:

  • Current whole life carbon assessments show the upfront embodied carbon is on track to achieve 300kg/co2e/m2which is less than that of the LETI 2030 upfront carbon target (350kgCO2/m2). This has been largely achieved through retaining the existing structure and façade, whilst trialling new low-embodied carbon and circular innovations.
  • Operational use: effective lighting and mechanical equipment, all-electric power supply with 100% renewable energy procurement. On-site renewable energy produced from solar PVs, blue roofs and sustainable urban drainage systems.

Resource use:

  • There has been a 29% embodied carbon saving through retaining the brick façade, equivalent to 59 tonnes of carbon equivalent emissions (kgCO2e). (1b)*
  • Specifying 34% steel from reused resources has accounted for a 60tCO2e saving in upfront carbon (in comparison to OneClickLCA’s generic Structural Steel profile (20% recycled content)) approximately a 6% saving in upfront carbon impact. However, this did have an increased cost due to extraction from the old site, transportation and testing for reuse. (1b) *
  • Other reused materials include York stone pavers for ground floor entrances which have a 3.2tCO2e saving in upfront carbon (A1-A5). (1b)* 99.95% of strip out waste diverted from landfill and traded on the re-use marketplace Globechain, the timber removed from the building has been donated to St Albans wood recycling charity, and some carpet tiles have been shared onwards. (1c)*
  • The space has been designed to be flexible with the CLT extensions allowing the floorplates to be adapted in the future. The MEPH plant has planned preventative maintenance to extend to lifespan of the plan and exposed finishes elsewhere in the building allow for easy maintenance and flexibility to zone future spaces in different configurations. (2b)*
  • Elements of the building have been designed to be disassembled at end of life through mechanical fixings and lime mortar which can be cleaned off the bricks. (2d)*
  • Although the use of standardised products has been limited through reuse of the building prefabricated kitchen unites and MEPH kit of parts have been standardised to allow modular building and removal. (3)*
  • Materials with high recycled content including CEMFREE concrete and Cross laminated timber have been used to lower carbon although both may have a cost uplift. (5b)*

Nature and biodiversity:

  • Increase in biodiversity with 11% of the building’s GIA is to be green space that supports the Wild West End initiative and UGF of 0.26.
  • Using the Defra Metric a Biodiversity Net Gain on site of 200% increase has been achieved.

Health and Wellbeing:

  • Mixed-mode ventilation with windows openable. Circadian lighting reflects natural daylight cycle.
  • 70 bicycle spaces.


  • Donating surplus materials: carpet tiles + timber doors / panels donated – Globechain + Community Wood Recycling.
  • Surplus materials are being distributed locally.
  • Extensive ground floor vegetation and green walls – improved local amenities and air quality.

Key Sustainability Objectives/ Outcomes

  • Aligned with the UKGBC’s Net Zero Carbon Buildings: A Framework Definition.
  • Acting as a LETI Pioneer Project.
  • Aligned to NABERS methodology.
  • Targeting BREEAM Outstanding, WELL Gold and Wired Score Gold certifications.


* This project is included in the “How circular principles impact Carbon and Value” report.

Notable Approaches And Solutions

  • The brickwork has been designed for deconstruction with new bricks being assembled using lime mortar which can be cleaned off at end of life, enabling the bricks to be reused. The Lime culture is estimated to have 20% less CO2 emissions than cement manufacturing and will absorb CO2 over the hydration process, meaning over time it will become carbon neutral. (2d)*
  • The steelwork is also designed with mechanical fixings so it can be deconstructed at end of life. (2d)*
  • Cross Laminated Timber is being used for the roof extension Which is also assembled with bolted connections to allow for deconstruction (2d). However this can be more expensive but was offset by comparative advantage on programme and sustainability credentials.*
  • CEMFREE concrete: can save up to 80% embodied carbon compared with conventional concrete mixes.* But there can be a potential cost uplift depending on the element and an impact on programme time due to longer curing period.
  • Thermalite aircrete blockwork.
  • Reclaimed raised access flooring, feeding into our wider                      re-use network.
  • Anti-bacterial and air-purifying tiles in toilets.
  • A conscious decision was taken to retain and refurbish the existing building for environmental reasons. However, the Reuse of the original structure has meant that the flexibility of the building has been impacted. If the building was demolished and rebuilt, there would have been the opportunity to have a larger floorplate which would have a created a more flexible product long term. (2b) *

The use of Circular Principles and other measures to reduce the embodied carbon will reduce the level of carbon offsetting once the project is complete. This could offset some of the price uplifts seen from some of the other innovative approaches taken on this project.

Lessons Learnt

When repurposing materials between existing development projects including Holbein Gardens we discovered a gap in industry knowledge and networks for the re-use of materials more broadly. To overcome this, in 2021 we canvassed 120 built environment professionals, representing the full lifecycle of a building, to find out more about the prevalence of, and barriers to, accelerating material re-use. The results were showcased through a series of educational webinars and supported the creation of a re-use network which now has over 700 active participants who can request or advertise specific materials. We are also working closely with industry forums such as SteelZero, of which we are a founding member, to further support the transition towards net-zero steel and material re-use including addressing the challenges associated with procuring low-embodied carbon steel and implementing steel re-use.

  • There was an original ambition to use recovered bricks for the façade, but there were quality issues which meant they could not be used; the challenge with reused items is that the quality is not assured for the scale needed on this type of project*
  • The reused steel was more expensive due to the cost of extraction from the old site and the transportation for testing before they could be reused *

Availability of data is improving, but product EPDs do not always have complete info which can impact carbon reporting. *