The side rooms were arranged one above another in three levels of thirty rooms each. There were ledges all around the wall of the temple to serve as supports for the side rooms, so that the supports would not be fastened into the wall of the temple itself.
Jewish Publication Society of America Version (JPS1917) - Ezekiel 41:6 >And the side-chambers were one over another, three and thirty times; and there were cornices in the wall which belonged to the house for the side-chambers round about, that they might have hold therein, and not have hold in the wall of the house.