Now we live in a lovely but much smaller house where I still have an office, but it is inside the house. We've been here for 9 months so far, and we have still not really figured out the details of how I can still "go to work" the way I used back in Philadelphia. My wife only has to speak here, somewhere in the house, and I can hear her.
This may improve when some specific physical details are addressed, but I think they won't solve the whole problem, which is a psychological/emotional/relationship one: how to be in the same "space" as someone else but also make it clear that you're not available.
We figure out the schedule of the day before I head "in", we communicate via text, and if that fails typically it's a knock at the door just like in an office. I also mention when I have big meetings or other face-time meetings so there's awareness.
That said, after all of that it was really the threshold for things that caused interruptions was what took the most adjusting.
Most of the day I wear headphones and listen to music, which is helpful - you don't feel compelled to shout answers or run down and help unless the person asks. Eventually though we found our rhythm, and it works well. And we both appreciate that when we need each other, we're right there, and that's great.
The big thing I need to improve on is simply getting outside more and going for walks during the day. A significant part of my commute was walking and now that's gone.