You know, thinking about fanfiction houses makes me realize they're basically narrative shortcuts with walls. They take all those abstract relationship tensions and pin them to a physical space—who sleeps where, whose mess is in the common room, who's always in the kitchen at 3 AM. That proximity forces interactions that might never happen otherwise, and it makes conflicts immediate and inescapable.
I saw this done really well in a 'Harry Potter' Slytherin!Harry fic. The writer put him in the Slytherin dorm, obviously, but then surrounded him with Draco's cronies and a few neutral pure-blends. The conflict wasn't just ideological; it was about sharing a bathroom and having your potions notes 'accidentally' get wet. The house became a pressure cooker, and the dynamics shifted from grand political stands to petty, personal grudges that felt much more real. It's a device that takes big, fandom-wide ship wars and boils them down to who ate the last slice of cake.
Honestly, sometimes the house itself almost becomes a character, with its own mood and rules that shape everyone inside.