Abstract: An imitation weatherboard assembly has two or more weatherboard elements (1) of plastics material which simulate overlapped weatherboard and a preformed backing sheet (11). The backing sheet (11) has a front surface (12) which, in use, abuts the back surface of the weatherboarding elements (1), the front surface of the backing sheet being formed to conform to the rear profile of the imitation weatherboarding elements so that the backing sheet (11) establishes contact with a significant portion of the rear area of the weatherboard elements. A planar edge (8) along the upper edge of an element (1) engages a slot (13) formed in the front of backing sheet (11).