Steel-framed addition with glass roof and upper floor platform The extension, approximately 2.1m wide and 4.5m long, slots between the brick walls of rear extensions to the terrace. It is a storey lower and set back 500mm from the original building line.
The glass roof consists of four double-glazed units silicone-bonded to concealed aluminium frames. They are fully supported on the wall sides by 130mm deep, steel flats bolted to the walls, and on the other sides by 90 x 44mm T-section beams, which span between the flats.
The rear wall is glazed with W20 steel-framed windows. , screw-fixed at the sides to vertical 130mm deep steel flats bolted to the walls.
At the eaves a 130 x 120mm welded steel angle runs above the window frames to restrain them. It is bolted through welded end plates to the 130mm wide vertical steel flats, and faced with a folded aluminium fascia.
The vertical and horizontal flats are bolted together behind the eaves with steel connector plates.
The glazed roof has a slope of 3infinity from the eaves to a concealed gutter at the junction with the existing house. It is formed of 3mm folded aluminium plate fixed to the wall and dressed with lead. The glass floor platform, a panel of 31.5mm three-layer laminated glass, is bonded to steel channels and angles with black silicone, its edges resting on black rubber spacers.The steel channels are supported at the corner on a 60.3mm diameter column.
The staircase consists of a pair of 10mm thick steel strings cut to take the shape of the treads and risers. A series of 30 x 30mm angles welded to the string, support steel Zshaped tread and riser units.
The 740 x 240mm maple treads are screwed to the Zshaped units from the underside.