160 Tooley Street, London

160 Tooley Street is a mixed-use development of nearly 20,000m², constructed for Great Portland Estates. The design represents a significant departure from the ubiquitous office format of the past, embodying current thinking on energy efficiency, whole life performance and other sustainability issues. The development combines new build and refurbished areas, and provides six floors of speculative office space, plus a variety of retail units on the ground floor and five residential units.

The project team set out to design and construct a premium quality, low-energy building with extensive use of off-site manufacturing, few following trades and minimal site waste. In meeting these aims, the team adopted a holistic approach that integrated structure, building services and architecture, using existing technologies and materials in innovative ways.

The most visible evidence of ‘the lean office’ approach is the exposed concrete interior, comprising precast soffit panels and columns with a high quality fair-faced finish. Suspended ceilings were avoided, resulting in most of the services (including the low-energy displacement ventilation system) being located in the floor void. Overhead services comprise lighting and fire alarm system, with the primary and secondary distribution trunking located in the recesses between the soffit panels.

The result is a space with a generous floor-to-ceiling height. Thermal mass provided by the exposed concrete helps optimise the building’s passive cooling performance and provides radiant cooling that compliments the convective cooling from the displacement ventilation system.

The precast concrete soffit panels measure 3m x 3m x 50mm and were used as permanent formwork to a 300mm post-tensioned slab cast directly onto them. This approach enables the exposed surface of the soffit to be produced in factory conditions helping ensure good control of the overall finish. The concrete mix for the panels contained white limestone fines for colour consistency and microfibres to minimise cracking.

In internal areas, the floors are supported on hollow precast concrete columns, which serve as structural ducts delivering air from the roof top plant to the floor plenum. This novel approach to air distribution eliminates the complex ducting that would otherwise be required to distribute air from the central risers.

The cross-sectional area of the hollow columns is greatest at the lower levels in order to support the weight of the upper floors,whilst the internal diameter is greatest at the top of the building, where it must deliver air for all the floors from the roof plant. There are progressive reductions in internal diameter at each floor corresponding to the diminishing volume of air carried and the increasing weight supported.

This provides an efficient solution, with the external diameter of the columns maintained at 1.05m and the inner diameter reduced in three steps through descending floors from 0.8m to 0.7m and then to 0.55m. Storey-height sections of the hollow columns were precast off-site to assure quality control.

Each section was cast vertically with self-compacting concrete being pumped in through valves in the base of the mould in order to eliminate voids and ensure an excellent finish.