Johnson Building

The project comprised the partial demolition and renovation of a building originally constructed in 1930, with the construction of entirely new sections and expansions. The client's brief called for a maximisation of area intended for commercial leasing and to create a corporate environment that would attract top companies. A permit for change of use was required and, despite not being located in a historical conservation area, the regulations required that the character of the region be maintained, which prevented changes to the two external façades facing the streets.

The larger office building lies at the front of the site, facing Hatton Garden, with St Cross along the side. The back wall, which had suffered bomb damage during WWII, was removed: the existing floors attached to it were demolished, along with the stairwells and elevators. This was done to expand the useful area, through the definition of new storeys, as well as allow the conceptualisation of a rational, flexi-plan space, instead of being tied to the original, fragmented layout. Six new storeys were inserted, with their tapered form ensuring that the rights of light for the neighbouring buildings were maintained, resulting in a diversity of spaces with double and triple floor-to-ceiling heights. The office area is concentrated in a ring around the atrium, which stretches from the ground floor up to the ETFE roof cover that ensures plenty of natural light, constituting the central element of the design concept. Precast concrete bridges inset with circular glass lenses span the atrium to connect the new office floors with the renovated, existing ones set into the frontal façades. An extended threshold cuts underneath and through the existing façade on Hatton Garden, acting as the building's main ground-floor entrance and leading past a reception before reaching the atrium. The decision to integrate the existing with the new in this project led to a 6,500-square metre increase in office space.

The smaller renovated building at the back of the site houses 14 flats and 150 square metres of jewellery workshops – a condition imposed by the planning authorities as part of maintaining the region's use characteristics. An internal, open air patio connects the two buildings and is often enjoyed for breaks by users of both.

As well as being a model for delivery on a tightly constrained site (the only site entrance was at the end of a narrow alley leading from Leather Lane, which required highly complex construction planning and site administration), the building has set new standards in the speculative office market in terms of quality and cost.

Development

The client's decision to create an office building in an area traditionally known for jewellery and precious metals was a risky one. In addition, the concept employed the use of exposed concrete with overlapping elements in wood, glass and stone – hardly usual in the corporate world. This meant that cost reductions and high quality became essential and the client shared the vision that the time and money spent on the development phase would yield enormous cost benefits for the project. Thus, extensive testing and the construction of full-scale mock ups were financed, allowing for materials, forms, finishes, and so on to be trialled during the design project. The main mock up, covering approximately 100 square metres, was used to reproduce key elements, such as offices complete with flooring, ceilings, lighting and internal walls; external walls and windows; bathrooms with all the finishes and lighting; and the atrium, with bridges, glass doors, guardrails and balustrades. It was constructed on a different site, owned by the same client, and which was also under construction in London. This and a process of constant pricing by the budget and cost consultants, along with participation by the client, ensured the complete definition of all the construction elements to achieve as strict a total project cost as possible.

In parallel, and as part of the same process, the contractor came on board at the end of the draft design project stage, working with the architects and consultants in the cost engineering process and helping achieve significant cost benefits and ensure high quality, with the final construction costs coming in at an exceptionally low value of £1,313 per square metre.