Slimdek was chosen for this tight infill residential development of 42 luxury flats in central London, partly re-using the listed external walls of the existing building on the corner site. Excellent acoustic insulation of the Slimdek floor was demonstrated by on-site tests.

Steel framing is increasingly being used in city centre residential buildings, particularly on tight sites where access and space for storage and handling of materials are at a premium. In these residential projects, speed and quality of construction are important. In addition, such sites often have restrictions on use of existing foundations or the size of new foundations, which favours the reduced self weight of steel solutions when compared to reinforced concrete.

Harleqin Court, located at Covent Garden in Central London, is a new-build and refurbishment project by developer Artesian providing 42 new high quality apartments for sale. The four to eight-storey building consists of about 4,000 m² of refurbished structure and 2,000 m² of new-build, which partly retains the existing masonry façade. It creates a new residential building with additional retail and commercial space on the ground floor.

Block C is the new-build part of the project and consists of 20 apartments built using the Slimdek floor system. The Slimdek system was chosen for its speed of construction, reduced floor-to-floor heights, and reduced loading, The Slimdek design consists of spans of generally about 5 metres to 7 metres for the beams and about 5 metres for the deep composite decking.

The design features a round central courtyard which has a highly glazed façade and includes balconies from some apartments. The façade onto Tavistock street is listed and had to be retained, so the Slimdek floors were constructed to about the inside face of the masonry and the steel columns were set slightly back from the wall.

Construction details

The eight storey steel frame consists typically of 203 mm UC columns generally on a five metre grid with 280 mm Asymmetric Slimflor Beams (ASBs) supporting SD 225 decking to create a 300 mm deep composite floor slab. At these spans, the decking does not require propping during construction. Bracing is provided by a concrete lift and stair core, and fire resistance to the columns is provided by 25 mm of mineral wool and 12.5 mm fire-resisting plasterboard.

To achieve excellent insulation against impact sound transmission, the floor covering consists of 35 mm of dense mineral wool and 18 mm thick chipboard. Ceilings consist of 12.5 mm thick plasterboard fixed to the underside of the deck using a proprietary fixing system with a small void between the deck and plasterboard for services. This gives a compact overall ceiling to floor zone of about 400 mm, and services can be accommodated between the ribs of the decking. Post-completion acoustic tests showed that the floor achieves very good acoustic insulation, considerably better than both current and proposed future Building Regulations requirements.

Seperating walls consist of light steel double stud construction using 2 x 75 mm steel studs with 25 mm of mineral wool within one side and 19mm plasterboard and 12 mm sound resistant plasterboard finish on both sides. Where possible, separating walls align with beams but where this is not the case, special details are used to ensure that the space between the ribs of the decking is closed off for acoustics and fire purposes.

External walls consist mainly of 215 mm blockwood finished externally with 60 mm EPS insulation and a proprietary acrylic render, and internally with dry lining plasterboard. One elevation consists of an existing masonry façade, and the courtyard features a glazed façade.

Key information

Number of storeys	4 - 8
Flats	42
New-build home

    Slimdek proves its Colours at Harlequin Court, Covent garden