Commentary for I Kings 6:6

The bottom chamber. One each side there were three [tiers of] chambers, one on the other. The measurement of its length is not stated here, but in Maseches Midos¹⁴ 4:3. we learned that there were thirty-eight chambers, fifteen in the north, five on top of five and five on top of them, and the same was in the south. And eight in the west, three on top of three and two on top of them. The bottom ones were five [amohs wide] and the middle ones six, and the top ones seven. Why? Because he made depressions in the wall of the house round about on the outside. The height of the chamber was five amohs, and as the height of the wall of the Sanctuary reached five amohs, he decreased its thickness and recessed it one amoh inward, and on that recess he placed the ends of the beams of the roof at the top of the chamber which served as the floor of the middle one. And as the wall reached [the height of] ten [amohs], he recessed it [another] amoh to place the ends of the beams of the roof of the middle [chamber] which served as the floor of the upper [chamber]. Thus we find the middle [chamber] is wider than the lower one by one amoh, and the upper [chamber] is wider than the middle one by one amoh.

So that [the beams] would not be attached to the walls of the Beis Hamikdosh. In order that the ends of the beams do not attach [to the walls] through perforations in the walls of the house, since this deteriorates the wall and it diminishes its beauty.