I've found that whenever I'm writing a lot of scenes that take place in the same house, it's much easier to have a visual floor plan to go by, not just for the practical issues of how to get the characters to move from one room to the next, but also for more subtle imagery, like how the sun would light up a room at a particular time of day.
The house in my current WIP was not an easy one to design because it takes place in a grand estate in New Canaan. I've got floor plans for multiple floors as well as one for the yard and out buildings.
Truth be told, I had a little too much fun looking through websites of New Canaan real estate while I was dreaming up this house. In fact, I fell in love with the house that I based the one in my book off of. Now I just have to come up with five and a half million dollars, and I can make it mine in real life too.