30 Grosvenor Square

The completed eight-storey build will sit over a three-storey basement, collectively housing 37 rooms and suites for guests, dining and entertainment spaces, a spa, six retail spaces and a grand ballroom. A highly-complex scheme, the works include part-demolition and façade retention of the original Grade II listed building, alongside preservation of iconic statues and other assets. Renowned British architect, Sir David Chipperfield, oversaw the design.

Appointed by Multiplex, Careys are delivering the extensive sub-structure and super-structure works; this follows on seamlessly from successful design and delivery of the significant enabling works package. Awarded by Qatari Diar, Careys were employed as Principal Contractor for these initial works which included creation of a new enlarged basement perimeter including:

• Capping beam
• Part top-down construction elements (propped slabs at ground floor, B1 and B2 levels)
• Retaining the historic facade and diagrid floor
• Refurbishment and demolition
• Asbestos survey and removal
• Structural alterations

The current sub-structure works include design and construction of the level 3 basement raft slab, 13 suspended slabs (six post-tensioned), and exposed diagrid slab and beam structure from level 2 to roof level. Local mezzanines have been designed in above B3 and B1. Ultimately B3 will be used as a plant room and car parking with the B3 mezzanine used exclusively for plant equipment. With B2 housing the ballroom and spa, the slab will be recessed to enable isolation of acoustics. At B1, the eastern side will contain lower level duplex retail units, accessed from the ground floor. The remainder of B1 will be used for the hotel ‘back of house’ services in addition to a void to the double height ballroom space. A large staircase is being constructed in the centre of the basement, which will contain large air louvres/ light wells running from the ground floor to B3.

In parallel, the team are delivering four cores, two of which are being slipformed.

The ground floor will house a mixture of retail and back of house space including a loading bay, with four different entrances. The ground floor is being framed by perimeter cruciform columns, spaced at 3.4m centres to match the diagrid floor grid at level 2. Level 1 will be accessible from a spiral staircase at the side entrance connected to a wide feature staircase at the main ground floor entrance. A large central atrium will be constructed at the top of this staircase spanning all the way to the roof. Above level 2, the existing stone facade is being retained, with new columns placed behind the existing facade to allow for a thermal break between the new structure and retained facade.

Levels 2-6 will be used exclusively for hotel rooms with a central atrium. Two cores, containing lifts, staircases and risers, are being constructed in the centre of the building on either side of the atrium. The building will step back at level 7 to form penthouse suites, which will be framed by an external colonnade around the perimeter of the set-back structure.

All works packages have been designed and delivered efficiently using BIM, which has proved invaluable for clash detection on this complex development. During the enabling works phase, 3D and 4D models enabled high accuracy comparisons of scans against historic data, culminating in a 5% saving to steelwork and a 3-week reduction in critical path activities.