Iowa Code § 563.5: Beams, joists and flues.

Every coproprietor may build against a wall held in common, and cause beams or joists to be placed therein; and any person building such a wall shall, on being requested by the other coproprietor, make the necessary flues, and leave the necessary bearings for joists or beams, at such height and distance apart as shall be specified by the other coproprietor.