Century House, near London's Waterloo Station, is famous for being the former home of MI6. Since 1998, the building has not been occupied, but it has now been converted into high quality luxury apartments and housing by developer Crest Nicholson. The existing concrete framed building has been completely stripped out and re-clad to a design by Assael Architecture. New light steel infill walls provide the external envelope and compartment walls between apartments, and a 2-storey roof-top extension provides new luxury penthouses with panoramic views over London. 

There were three phases to the project: the first was the renovation of the existing 20-storey building, creating 9 apartments per floor, together with a 2-storey roof-top extension; the second was the renovation of a 5-storey building including 16 apartments; the third (for shared ownership) is a new building acting as a reception and below-ground car parking area. The conversion and new-build created 80 residential apartments for sale and a further 56 apartments for Metropolitan Home Ownership.

The cladding to all buildings is a combination of a metallic cladding panel and a lightweight terracotta tile system which are attached to horizontal rails screwed through the external insulation to the light steel infill walls. The light steel C sections provide the required resistance to wind loads and support the self weight of the cladding. The infill walls are installed on-site in order to accommodate the dimensional inaccuracies of the existing concrete frame. Importantly, the lightweight walls do not overload the existing structure, allowing two additional floors to be built for the same self weight as the former concrete block walls.

The internal compartment and partition walls have been designed to give excellent acoustic insulation and fire resistance properties when finished with two layers of fire resisting plasterboard per side. The same insulation also reduces external noise from the nearby Waterloo Bridge Road. The ‘warm frame' construction ensures a high quality internal environment.

According to the general contractor for the project, Pearce Construction, it is the largest project in the UK to be renovated using light steel framing. The overall construction value is £40 million and the complete construction programme for the three buildings was 3 years to occupancy.

There are three buildings in this major project, two of which posed the following challenges in their renovation and upgrading to modern standards: l

• Removal of internal concrete shear walls;
• nfilling of existing service risers;
• New penthouses as a roof-top extension;
• New lightweight cladding to transform building appearance.

The existing structure consisted of hollow-core floor slabs, spanning from a spine of central service cores to spandrel edge beams. Stability was provided by shear walls and by framing action between the spandrel beams and edge columns.

Lightweight infill walls using 150 mm deep C sections were used in the renovation in order not to over-load the existing floor slab (this would not have been possible in dense concrete brickwork). Service risers were in-filled with a new composite floor slab and steel angles bolted to the existing concrete structure, which avoided the need for propping.

The new 2-storey penthouse is supported by the existing structure. It is constructed in a lightweight steel framework, using RHS sections at the perimeter of the structure to support the upper levels. Fire protection was achieved using intumescent coating to preserve the crisp shape of the RHS sections, which act as window mullions.

A lightweight metallic and terracotta tile cladding system was selected in order to create the required architectural appearance, and to be constructed rapidly without over-loading the existing spandrel beams. The same system was used on the three buildings in the project.

Key information

Number of storeys	20
Apartments	136
New-build home

    Twenty-storey Towerblock is Transformed using Light Steel Framing