The “chamber of Johanan” was probably one of those attached externally to the temple (see 1 Kings 6:5-6). Eliashib was the grandson of Jeshua Ezra 3:2, and was high priest under Nehemiah Nehemiah 3:1. He could assign chambers in the temple to whomever he pleased (see Nehemiah 13:4-5).
Related Commentaries of Ezra 10:6
Ezra 10:6
6 Then Ezra rose up from before the house of God, and went into the chamber of Johanan the son of Eliashib: and when he came thither, he did eat no bread, nor drink water: for he mourned because of the transgression of them that had been carried away.