海角视频

50 Baker Street

London, UK

海角视频 supported an aspirational client team to answer the complex question of whether it would be more carbon efficient to refurbish and retrofit a mixed group of existing buildings on Baker Street, London, or to demolish and rebuild using the latest materials, technologies and systems.

A team of structural engineering, sustainability and facades specialists from 海角视频 was engaged to examine the challenge and deliver a carefully considered assessment worthy of Baker Street鈥檚 own most famous fictional resident Sherlock Holmes.

Challenge

When Derwent London looked to redevelop one of the last remaining development opportunity sites in Marylebone, the investor was faced with weighing up the relative merits between the retention and adaptive reuse of the site鈥檚 existing buildings, or demolition and rebuild.

Often planners鈥� instinct is that the retention and regeneration, or adaptive reuse, of a building must mean a lower embodied carbon footprint for the project. This is generally the case, with retention typically showing significant carbon savings over demolition and rebuilding.

But in some circumstances, this is not the case 鈥� particularly where the amalgamation of new structural elements with existing structural elements and poor performing fabric adds significant complexity and therefore carbon intensity. Every development project is different, and understanding which is the best route in terms of carbon reduction can be complex and nuanced.

With super-sustainable aspirations, both in terms of upfront embodied carbon and operational carbon, the client鈥檚 vision was for a predominantly commercial mixed-use city block that places sustainability at the fore of its plans. Our structures and team worked through RIBA Stage 2/Planning to aid the client with its decision making, with a particular focus on evaluating the existing buildings on-site and the merits of retention versus rebuilding. Further insight was later delivered by our facades experts to support the development of robust energy models.

Considerations included whether additional storeys could be easily added to existing structures, the structural merits of the existing column grids, the heritage value of the properties, the nature of the current floor-to-ceiling heights and the impact these might have on adaptive reuse options.

These considerations had to be weighed carefully against the relative benefits of a demolition and rebuild approach, with a particular focus on the impacts on carbon, to build a logical demonstration of which option would provide the most genuinely sustainable approach.

Solution

The development will generate a sense of place, promoting wellbeing, greening, and providing a larger number of affordable residential units as well as office and retail space. The rebuilt scheme effectively doubles the commercial area from its current 122,000ft虏 to a robust c.240,000ft虏. 

Extensive studies culminated in demonstrating, even from an upfront carbon calculation alone, the poor value in retention, which paved the way to a client decision to opt for an entirely new-build design. 海角视频 took a lead in discussions with local authority sustainability officers and planners throughout the process, with the scheme securing a unanimous resolution to consent planning approval in mid 2024 by the local planning authority.

The Baker Street site contains a mix of buildings from different eras of the last century, which we examined alongside metrics developed to evaluate the ability to meaningfully retain elements within the new design. We assessed that the southern building (Accurist House) had the potential to be retained and integrated into a new structure, but the carbon intensity of the different options around retention versus complete rebuild had to be carefully calculated. We examined a broad range of options about what could be retained.

Sometimes the amount of carbon saved in retaining the old can be lost in the complexities that connect the old structure to the new structure. The new build option enables regular column grids, structural modularisation and the elimination of unwieldy structural transfers.

Our innovative circular economy solutions include the reuse of existing concrete slab in the raft, saving 2,000m鲁 of concrete.

As well as assessing the impact on embodied carbon, considerations also had to be made around the operational carbon of the future building 鈥� with the potential efficiencies of new systems, across an entirely new building鈥檚 lifetime, weighed against the retrofitting of new systems into a partly historic structure. We determined that an optimised new build has 19% lower base build operational energy demands than a retained Accurist House and has 56% lower operational energy demands than the existing building.

Our report carefully broke down the figures for each option, including the impacts of different design decisions to refine the data, such as changing to a raft slab foundation 鈥� an option not available in the retention model, but which would be available in the rebuild model. The process overall allowed for a 14% embodied carbon saving over the GLA aspirational target, with the carbon-optimised new build scheme delivering 532kg CO₂e/m² GIA, compared to 551kg CO₂e/m² GIA for the alternative that retained a larger element of Accurist House.

As well as providing a detailed assessment of 鈥渞etain versus replace鈥� strategies, we also produced the detailed figures for an option where the Accurist House is kept as a separate structure. But once again, the new build option came out with the best carbon value when all intervention aspects were considered.

We are also using the frame to temper the internal environment by embedding water coils inside the slab to use the thermal mass of the concrete to regulate the temperature peaks and troughs and ensure the maximum wellbeing of occupants. The design will also maximise natural ventilation and daylighting, to further support the comfort as well as minimising the operational carbon intensity of the new building by limiting the requirements for mechanical cooling.

The project is targeting BREEAM 鈥淓xcellent鈥� for the office and retail, with a pathway being explored to achieve 鈥淥utstanding鈥�, as well as LEED Platinum, Well-enabled, Home Quality mark 4.5 stars and WiredScore Platinum. It is also targeting NABERS certification at a minimum of 4.5 stars. With the provision of 17 residential units on the site, the development is classified as a Higher Risk Building under the new Building Safety Act 2022. Our team played a key role in ensuring the design meets these regulatory requirements.

Value

We acted as trusted advisors to the client, building a clear picture of the carbon impact of different design options and leading articulate and informed conversations with planners.

Our starting point was to retain and redevelop as much as was feasible. However, detailed analysis showed that the majority of the existing buildings did not allow for the delivery of quality space as well as public and social benefits, and critically that in this particular instance, the most efficient use of carbon came from the option that delivered an almost entirely new structure.

Our experts in structures, sustainability, including energy modelling, and facades have come together to develop a science-backed narrative for planning.聽 Future-proofing the design through a 鈥榰se for longer鈥� philosophy, we developed a series of strategies to ensure the new space would generate a sense of place, promote wellbeing and greening and be flexible and adaptable ensuring a practical lifespan of more than 60 years.