Abstract: The invention is an apparatus and method for assembling a planar surface for multiple sheets of building material connected by multiple retaining clips. Each of the retaining clips comprises a first portion and a second portion. The first portion has a first receptacle defined by a central wall and an upper and lower flange. The second receptacle is defined by an opposite side of the central wall and a second lower flange. A first sheet is inserted into the first receptacle through the open side between the upper and lower flanges and opposite the central wall. A second sheet is pivoted through the open sides of the second receptacle, which are opposite the central wall and the second lower flange. The second portion comprises a T-shaped element having opposing tabs extending from a retaining tongue. The opposing tabs are received within a slot on the first portion such that the retaining tongue overlies the upper surface of a second sheet and closes one of the open sides of the second receptacle.