In 2006, I tore off a family room that had been added onto my existing 1922 bungalow. I rebuilt the room then built up over that space and tied into the existing attic to add three bedrooms and two bathrooms. During the project we also remodeled the downstairs bathroom. They had to dig a new foundation for the family room/upstairs addition plus we strenghtened the existing beam under the house. I put new siding on and a new roof over the entire house, upgraded the electrical connection, basically repiped the house and redid the water connection to the street. In reality, I spent more money on the stuff you don't see than the stuff you do. My girls, then 7 and 4, and I lived in the house during the process. Was it fun? Not a chance, especially the two nights while the roof was off when we had big storms and water everywhere. Thankfully I had great contractors who fixed everything. Was it worth it? YES! I love my neighborhood and the extra space is fantastic. I didn't need to add as much space as I did but my architect came up with the plan and with a little cutting of some details and stretching the budget by my taking on certain things, we were able to make it work. Did it damage the existing house? No, not at all. In fact with the new beam, the house is actually supported better than it was. When you are ready, get an architect. It's totally worth the money because they will have ideas that you'd never think of. Discuss fully everything you'd like to do as you can always cut projects. That way when the plans go out to bid to the contractors, you'll have a realistic idea of what you are spending. The first bids on my project were scary but with some changes, it was doable. Remember, you will run into unexpected expenses-granite in the master bath, a wooden staircase are two of the things I ended up adding but I didn't add more than 2% of the budget. It will take longer than anticipated!!!!! No matter how well they plan, things will not go according to schedule. So be prepared for the long haul. Good luck!