C. F. Keil and Franz Delitzsch on 1 Kings 6:15

1Ki 6:15 “He built (i.e., so far as the sense is concerned, he covered) the walls of the house within with boards of cedar; from the floor of the house to the walls of the ceiling he overlaid it with wood within, and overlaid the floor with cypress boards.” The expression הסּפּן קירות, “walls of the ceiling,” is very striking here, and renders it probable that קירות is only a copyist’s error for קורות, “beams of the ceiling.” The whole of the inside of the house was covered with wood, so that nothing was to be seen of the stone wall (1Ki 6:18). On the other hand, the biblical text knows nothing of any covering of the outer walls also with wood, as many have assumed.