Acts 1:13

They went up into an upper room - This was either a room in the temple, or in the house of one of the disciples, where this holy company was accustomed to meet. In Luke 24:53 , it is said that, after their return from Mount Olivet, they were continually in the temple, praising and blessing God: it is probable, therefore, that the upper room mentioned in this verse is that apartment of the temple mentioned above. But still it is not certain that this place should be so understood; as we have the fullest proofs that the upper rooms in private houses were used for the purpose of reading the law, and conferring together on religious matters. See several proofs in Lightfoot. Add to this, that the room here mentioned seems to have been the place where all the apostles lodged, οὑ ησαν καταμενοντες , and therefore most probably a private house.