What are the principal advantages of using a single building information model of the existing conditions as the foundation for modeling several proposed design alternatives for a portion of the building? Why not create a separate model for each of the design alternatives?
It is helpful to have the previous foundational model so that you can see how the designs interact with each other. It helps to show the whole broader picture of the design, particularly how the components of the model interact and look with/near each other
What sort of complexities are introduced when you construct a building complex in phases? What happens at the interfaces between the buildings as the phases advance? How can you plan and prepare for these complexities as you create your initial building model?
Complexities include the demo phases and whatever new components are added. The interface can be seen between the phases as they interact with each other, especially in my building where there is a second floor landing directly connected to the existing building.