Room-over-room

Room-over-room designates methods allowing level design which transcends Doom's ordinary engine limitation of one floor height and one ceiling height at any given location on the (x, y) plane. Creating a room above another room is normally impossible, though the effect can be faked to a limited degree in the ordinary Doom rendering engine through various tricks, such as moving sectors, as in Industrial Zone's south-east building, or via self-referencing sectors. Through advanced source port features, notably 3D middle textures, 3D floors and portals, more fully convincing effects are possible.

The earliest implementation of room-over-room, provided by the RORDoom source port in 2000, allowed sectors to overlap. This approach is not in general use now.

Doom 64 simulates a room-over-room effect by changing the floor and ceiling heights of sectors via macros, depending on the direction from which the player approaches an area. This effect is noticeable while using a no-clipping cheat in Doom64 EX, since the sectors will not change properly. Such an approach is incompatible with multiplayer games; however, Doom 64 itself had no support for multiplayer.