A delicate steel and timber stair forms the centrepiece of a north London house renovated by AY Architects. The existing building, located at the end of a parade of shops in the Dartmouth Park Conservation Area, had previously been subdivided, and the architect was appointed to reconvert it into a single home.
“A process of opening up the building vertically and horizontally sought to create a series of spaces where context, daylight, views and outdoor space play a central role in the life of the house”, says the architect.
The design hinges around a three-story internal void housing a slender staircase that interconnects the house vertically and horizontally. This vertical open space links the street to the rear visually, extending the living spaces towards an upper level terrace that wraps around a new sunken courtyard.
“The delicately crafted steel-frame and timber-clad staircase is a functional and sculptural piece that theatrically animates the house on all levels”, says the architect. The stair – realised in collaboration with engineer Price & Myers – extends from basement to second floor level, and was constructed in a narrow space between the party wall and kitchen partition wall.
“The architects were keen to feature a gap between the stair and the party wall, presenting us with the challenge of finding continuous structural support without using the wall”, says Price & Myers. “In addition, the party wall was out of plumb and this needed to be accommodated within the design”.
The stair is constructed from a 10mm thick folded steel plate with two straight flights and two 180-degree bends in it. In order to provide some support for the stair, Price & Myers recessed in a steel ‘T’ section within the party wall, which spanned vertically from ground floor to roof level. Steel angles were then welded to the ‘T’ section to support the stair.
“We worked closely with CSI in Hull to put together a load and deflection test, as we thought the stair might be quite lively with such minimal support”, says the engineer. A segment of the stair was loaded with sand bags and the deflection measured, with the results well within the safety margin set by the calculations. “With these results, it was possible for us to further reduce supports in order to define the gap and create an unusually slender structure”.