Charles Ellicott Commentary Ezekiel 41:9

"The thickness of the wall, which was for the side-chambers, on the outside, was five cubits: and that which was left was the place of the side-chambers that belonged to the house." — Ezekiel 41:9 (ASV)

That which was left.— After stating the thickness of the outer wall of the side chambers at five cubits, the prophet speaks of the remaining space left unoccupied by the building. The clause should be translated, “and so also (i.e., of the same width) was that which was left free against the house of side chambers which belonged to the house,” i.e., to the Temple. The same width is assigned to this space in Ezekiel 41:11.