Picardi Architects' new staircase and mezzanine gallery are set within the volume of the pitched roof of this third-floor flat in London's Holland Park.
Around the staircase opening the gallery floor is formed of laminated glass panels; on the far side it is floored with t&g sycamore boards.
The gallery is set between the original walls, and a simple steel beam structure spans between them. It consists of a fascia beam, a 100 x 100mm SHS, and two inner beams which are 100 x 60mm RHSs. A 12mm glass balustrade runs at the edge of the gallery. It is clamped with a silicone seal between a pair of steel angles; an upper 90 x 90mm RSA is screwed to a lower 100 x 100mm RSA, creating a slot in which the lower edge of the glass is clamped.
The angles and the SHS beam are clad with a stainless steel fascia, which also accommodates cables serving a pair of downlighters. The balustrade has a 42mm diameter stainless steel handrail set onto the top edge.
The two laminated glass floor panels that fit round the staircase opening have a sandblasted top surface to give grip;
they rest on neoprene gaskets in a 25 x 25mm stainless steel tray/ frame fixed back to the beams.
The staircase is a spiral; it consists of a central 100mm diameter stainless steel column with triangular laminated glass treads and a helical string rising on the outside to support the treads and balustrade. Each tread is notched at the edges to slot into a triangular stainless steel tray. The helical string comprises a pair of stainless steel flats spaced with hardwood packers; the balustrade, a series of curved 12mm thick translucent acrylic sheets, is clamped between the flats. It has a curved 42mm diameter stainless steel handrail fixed to the top edge.