Definitely an Araneus orbweaver. I would guess that he’s a Cross Orbweaver, A. diadematus. They don’t usually build webs indoors but sometimes they get confused and wind up in places they shouldn’t be. I hope you moved this one outside.
Yes, this is Araneus diadematus, a studly young male. The males build webs when they are young, before they are mature enough to set out to find females. He might have been blown into the house on the wind when he left his mother and just instinctively set up camp. A little confused, as Galvantula said.