Charles Ellicott Commentary Ezekiel 41:12

"And the building that was before the separate place at the side toward the west was seventy cubits broad; and the wall of the building was five cubits thick round about, and the length thereof ninety cubits." — Ezekiel 41:12 (ASV)

The separate place. This is the space at the west end of the Temple (20 cubits wide) before reaching another building.

Nothing is said here about the purposes of this other building, but it is probably “the appointed place” (Ezekiel 43:21) for burning the sin-offering, and also any remains of other sacrifices that needed to be consumed by fire, and any other refuse from the Temple.

Its total width of 80 cubits (70 cubits + 2 walls of 5 cubits each) leaves a passageway of 10 cubits on each side; meanwhile, its length (90 cubits + 2 walls of 5 cubits each—100 cubits) just fills the space from “the separate place” to the wall of the court (see plan II, G., and Ezekiel 40:44-49).

The sum total of the exterior measurements is given in Ezekiel 41:13-14.