Abstract: A drainage arrangement in a dual wall including two leaves separated by a cavity. In one aspect the drainage arrangement includes one or more imperforate elongate members which are formed as a channel, the sides of which are adapted to be mounted to the opposed faces of the leaves of the wall. The one or more elongate members extend for the length of the cavity between the leaves to close the space therebetween and the channel opening into an outlet provided in the wall to allow the drainage of water from the elongate member through the outlet.