The side rooms surrounding the temple widened at each successive level, because the structure surrounding the temple ascended by stages corresponding to the narrowing of the temple wall as it rose upward. And so a stairway went up from the lowest story to the highest, through the middle one.
KJV
And [there was] an enlarging, and a winding about still upward to the side chambers: for the winding about of the house went still upward round about the house: therefore the breadth of the house [was still] upward, and so increased [from] the lowest [chamber] to the highest by the midst.
ASV
And the side-chambers were broader as they encompassed the house higher and higher; for the encompassing of the house went higher and higher round about the house: therefore the breadth of the house continued upward; and so one went up from the lowest chamber to the highest by the middle chamber.