Ezekiel 41:6-7

6These side rooms were built in three levels, one above the other, with thirty rooms on each level. The supports for these side rooms rested on exterior ledges on the Temple wall; they did not extend into the wall.

7Each level was wider than the one below it, corresponding to the narrowing of the Temple wall as it rose higher. A stairway led up from the bottom level through the middle level to the top level.