A method for laying a sheet over the lower surface of a base material disposed in a generally horizontal position. According to the method, the base material is supported at the lower surface thereof by a first support means, and the sheet is placed immediately below and in facing relation to the lower surface of the base material and then supported at the lower surface thereof by a second support means. The sheet and the base material are made to be in contact with each other over partial surfaces thereof. Subsequently, the first support means is moved away from the base material and the sheet and the base material are placed together on a rigid horizontal surface so that the sheet is laid substantially over the entire lower surface of the base material.