Exposed larch structure with mortice and tennon connections
This project involved adding a storey to an existing office building in Bermondsey Street, London. The original structure dates from the 1950s and consists of a concrete frame with a flat roof. The proposal was to provide a two-bedroom apartment accessed via an extension to the building’s existing stairwell by covering two-thirds of the roof area.
The new storey was created with full height exposed timber trusses following the profile of the pitched roof supported by the column of the RC frame below. To provide an efficient solution, the trusses were the full height of the new storey. Larch was used for all the compression elements (the top elements of the truss) and steel was used for all the tension elements (the bottom boom of the truss). This also enabled us to have mortice and tenon joints for all the timber / timber connections while achieving a slender floor zone by using a compact steel beam for the concealed bottom boom of the truss. Posijoist were added between the steel beam of the truss to provide the new floors to mitigate any strengething to the existing structure.
From the beginning, RISE thought about the sequence of construction and drew each detail to ensure the site erection would go smoothly.
The trusses support timber glulam larch purlins and loose timber rafters forming the roof. There is a high-level roof lantern over the central area of the new apartment, while at the back there is a private roof terrace. The new roof is fairly heavy and uses beautiful Welsh slate. A green wall features on one side of the property, while a sedum roof is provided elsewhere.
It was very exciting to produce a structure which usesexposed larch and exposed purlins, all integrating well within this beautiful space.
Images courtesy of Knight Frank Tower Bridge