Working Detail: Conan Doyle Medical Centre, by Richard Murphy Architects
[WORKING DETAIL 26.06.08] A monopitch roof with projecting eaves and a rainwater chain
The two-storey medical centre has a steel-framed structure with composite steel/concrete floors. The main roof element, set above lower areas of flat roof, is an overhanging monopitch with a continuous clerestory just below the highest part; it runs along the main entrance facade and turns at the corner to form an L-shape.
The monopitch roof is covered with a standing seam aluminium roof system with integral insulation and liner. At the upper and lower eaves and the verge the roof projects over the clerestory and glazing, reduced in thickness and tapering to a blade-like edge.
The roof projection is supported by a series of galvanised steel outrigger ‘arms’, Tshaped in section. They are bolted back to the steel roof structure and taper to the outer edges. A 200 x 100mm RSA runs at the top edges of the arms, welded and bolted to them to create the final blade-like edge. Behind, layers of exterior-grade plywood, framed and covered with a single ply membrane, form the connection to the built-up roof system.
Rainwater draining from the monopitch roof is directed into gulleys below by four galvanised steel chains that take the place of a conventional downpipe - a device that reinforces the delicacy of the overhanging blade edges to the roof. Each outlet consists of a circular frame spigot set in a hole with the four chains bolted to the inside: as they descend they are plaited together, terminating with a ring connector hooked to a gulley grating.