London
Seymour Mews House
Seymour Mews House is a refurbished office space in the heart of Marylebone, West London.
The existing five-storey, 31,000ft² building, dating back to the 1960s, featured a reinforced concrete frame. The proposed scheme included a complete refurbishment from the ground floor up, while the construction of a new roof structure would allow for a small extension of the fifth floor.
Client: UK & European Investments
Location: Marylebone, London
Completion Date: 2019
Architect: BuckleyGrayYeoman
Other Team Members: Heasmans
Challenge
The focus of this redevelopment was to update the tired 1960s exterior and remodel the interior spaces to create a more dynamic, contemporary working environment and a better fit to the neighbourhood surrounds with its mix of mews houses, cobbled streets, residential mansion blocks, Georgian townhouses, chic boutiques and stylish restaurants.
A feasibility study was required to determine the best options for refurbishment of the building for clients UK & European Investments, now known as Blue Coast Capital. This included investigation into the durability of existing concrete/stone cladding on the building’s exterior as well as recommendations for suitable overcladding/façade replacements. The heavy precast cladding was subsequently replaced with a lightweight SFS-type curtain walling system.
On the ground floor, the reception space was significantly improved by moving the line of the cladding to make the existing undercroft parking area internal, thereby extending the internal floor plan.
Solution
Further enhancements included the demolition of the existing lift shaft and construction of a new shaft to house a double lift, as well as the formation of a large riser to the rear of the double lift shaft to house new services for the building.
The existing roof slab and associated supporting columns on the fifth floor were demolished before a new steel frame roof structure with lightweight metal deck was constructed to allow for a small extension of the floor beneath.
Analysis of the existing structure showed that its stability was provided by the diaphragm action of the rigid reinforced concrete (RC) floor plates which transferred lateral loads to the vertical stability system. This was comprised of a shear wall to the RC lift shaft with calculations showing that the masonry infill walls within the structure were also contributing to the overall stability. Such infill walls are generally flanked by RC columns on either side which resist the push-pull effect of the shear wall.
In the redevelopment works, the existing core was replaced by a larger version to house the double lift, located very close to the position of the original. The existing structure was tied to the new core, while full-height steel vertical cross bracing was introduced to help the lateral stability. Some existing masonry walls were retained, along with stair core walls. Where required, the existing foundations were also strengthened.
The new transfer beams were pre-cambered for dead load deflection and the dead load jacked in using hydraulic jacks. This involved complex sequencing and temporary works, backed up with detailed calculation and analysis of each stage, with the building performing almost exactly as predicted as the loads were transferred from the old to new structure, without undue differential settlement or distortion in the building.
