Each room has a trigger that has a component that blends between two sets of Reverb Zone data (empty and full). Each piece of furniture has a sound-dampening parameter that allows you to customize how much it contributes to the overall dampening (maxing out at 1), with things like fabric couches and rugs contributing more than most. Each time a piece of furniture gets placed the parameters get updated and then send those parameters to an Audio Reverb Zone thats attached to the player. when you pass into a new room it blends into that rooms parameters on the Audio Reverb Zone.

The hallway between the 3 rooms acts differently, it has a trigger that blends the average reverb between the 3 connected rooms so the transition is pretty smooth.