Basement Whatever

One thing we’ve found very useful is to determine a uniform dimension for door frames.  This has a few benefits.  It allows us to transition from kit to kit without unique pieces, as well as allowing easy re-use of doors between kits.  More importantly, it gives AI and animation a fixed standard to work from, which can be reinforced throughout the game.
— Read on blog.joelburgess.com/2013/04/skyrims-modular-level-design-gdc-2013.html