London
17 Broadwick
The brief for the renovation of this modest but iconic building by world-renowned architect Richard Rogers was to update and maximise the existing building while staying respectful to the original design intent.
Built at the turn of the millennium and situated in the heart of Soho on the corner of Broadwick Street and Berwick Street – home to the famous Berwick Street Market – it was originally known as the Ingeni building.
Evolve were appointed to provide structural engineering services for the works which would include the creation of a new office floor to increase the overall office footprint. The introduction of dramatic, horizontal slot rooflights into the highly engineered curved roof would provide impressive views across the city, while two new roof terraces were to be cut into the curved roof to further enhance the building’s upper floors, alongside a new terrace at seventh floor level. New lift cars were to be installed to serve the new office floor, with a full refurbishment planned for all areas of the building apart from the existing ground floor restaurant.
Client: Private
Location: Soho, London
Completion Date: September 2021
Key Evolve Contacts: Neil Shiner
Architect: Hale Brown Architects
Main Contractor: Faithdean Plc
M&E Engineer: Taylor Project Services LLP
Sector: Commercial
Challenge
Inspired by Rogers’ early concept drawings, the design by Hale Brown Architects aimed to increase the internal office space by vertically extending the building on a portion of its footprint; relocating the existing plant rooms; and horizontally extending the seventh-floor slab into the existing double-height roof space with a 3.2m cantilevering mezzanine to reinstate the original concept and create a striking duplex floor overlooking Soho.
The renovation also included the complete reconfiguration of the downstairs reception area; the reconfiguration of the basement to provide additional space for the restaurant; and a CAT A fit out of the upper office floors. The existing panoramic glazed lift was also extended up to the new seventh floor office space.
Exposed structural steelwork forms a double-height curved roof supported on a six-storey flat slab concrete frame. The lift shaft is fully glazed with a very minimal structure supporting the guide rails and cantilever lift motor room.
Solution
Although originally built in 2000, only minimal information on the existing structure could be found. As a result, and due to the proposed changes to the roof steelwork, the curved steel structure was modelled in FEM software to allow for a greater understanding of how it worked, and to achieve a more refined design.
The curved roof is formed from three bowstring trusses spanning from the cantilevering edge of the sixth-floor slab up to tapered cantilever columns supported on the stepped back seventh-floor slab, creating a double-height space over the sixth floor. Lateral stability was provided by the tapered columns and a single bay of plan bracing in the curved roof, but the roof was flexible due to its nature. As part of the works, it was proposed that six rooflights would be added to the curved roof to bring light into the new seventh-floor office space. This presented a challenge – how to limit deflections for the brittle glazing in the flexible roof. The solution was to introduce bracing into all the remaining bays, including the cantilevering canopies at each edge.
The seventh floor was extended out into the double-height space using tapered cantilevering steel beams fixed to the existing seventh-floor slab edge. The deflections were limited to 5mm at the end of the cantilever to avoid the floor having too much bounce. A new feature staircase from the sixth to seventh floor mirrors closely with an original sketch by Richard Rogers and creates a link between the two floors. In addition to rooflights, new openings were made in the curved roof for inset balconies giving views over the city.
The existing scenic lift cars were replaced and extended to serve the new seventh floor, which required adaptions to the existing lift shaft overrun structure, which cantilevered up from the existing slab, utilising both vertical and plan bracing for stability. The new plans required the removal of some of the existing bracing and adaptions to the existing steelwork to accommodate the new lift cars. To minimise the amount of rebuilding required, the existing ring beams were cut and offset to provide an additional 75mm of width at the rear of the shaft alongside other adaptions. Hand sketches were used to convey the concepts to the wider project team.
A number of site constraints had to be considered during the construction period. The ground floor restaurant was to remain operational, while the site was landlocked by busy streets and footways making road closures for the delivery of materials challenging. The primary structural works were on the high floors which required cantilevering scaffolding; this had to be programmed to minimise the impact on the Christmas trading period for the market stalls on Berwick Street. The restaurant remaining open presented a challenge for the relocation of the plant to the new roof at eighth floor level. Careful programming to reduce the down time for the chiller meant that the seventh-floor extension was built around the chiller; it had to be lifted when the first section of the roof slab had been cast and cured to then allow for the remaining steelwork to be constructed before the chiller was moved into its permanent position.
The extension and renovation of such a landmark London building presented many interesting challenges – most notably with regard to its beautiful, curved roof – but it was a pleasure to help successfully deliver the project while keeping true to the original spirit of the building as conceived by Richard Rogers.
