Abstract: A prefabricated house is provided with ceiling panels that are the same size, have a longitudinal dimension equal to or greater than MP/m-D/m and a lateral dimension equal to or greater than NP/n-D/n where MP and NP are the longitudinal and lateral inside dimensions of the ceiling plane for one floor of the house, m and n are integers representing the number of ceiling panels longitudinally and laterally disposed, and D is the thickness of a partition panel, whereby upon assembly of the ceiling panels a gap of width less than D exists over the place where a partition wall is to be erected. Partition wall panels are also of uniform dimensions hence partition wall panels for doors are offset from the wall line to compensate for one wall thickness. The ceiling panels are provided with a unique construction which facilitates the installation of electrical wiring and hides all fasteners which fasten the ceiling panels to the ceiling joists.