So far as I can tell, the rules are mute on the matter of PvP. I even looked in the DMG earlier today to see if there was anything in the "Table Rules" section. It seems like if it was going to go anywhere, it should have been mentioned in that part, given as common as players wanting to mess with other players' characters is. A table rule gets people on the same page with regard to whether this is acceptable play at a given table.
Does that mean PvP is not an expectation of the game? I don't know. The rules talk about how "teamwork and cooperation greatly improve your party's chances to survive the many perils in the worlds of D&D," how adventurers work together in teams called a "party." I can find nothing in the books that talk about conflicts between characters and how they might be resolved mechanically. We're left to figure that out on our own, I suppose, using the rules provided as a framework.
I think I'd leave off on calling a "No PvP" policy a house rule though. I also wouldn't call what some of us do a "No PvP" policy either. You can definitely have PvP - the players just have to negotiate that out on their own in a way that is fun for everyone and contributes to an exciting, memorable story.