A wall is ignored when determining the room volume

Problem

When determining the room volume, one wall is ignored and the MEP space thus extends over two rooms.

Possible cause: missing room bounding

The wall was not defined as a room bounding component and is therefore ignored when creating the MEP space. The room extends across the wall accordingly.

Solution

If you have access to the architecture, activate the Room bounding option in the Properties of the wall in the architecture model.

Possible cause: partially suspended ceilings

This can similarly be true for walls with activated room boundary, e.g. if the ceiling was partially suspended. In these cases, note that the base surface of a wall are not recognized as room boundaries in Revit. As the MEP space expands from bottom to top, it extends through the base surface and into the wall.

Solution

This problem can usually be solved in the architectural by modifying the ceiling structure. After the modification, the base surface no longer hangs in the open space, but rests on the suspended ceiling, as shown in the following figure (left: before, right: after):