Here is my question folks, I have a single story home with a lot of room in the attic. I'm pretty sure my ceiling is capable of supporting a 2nd level, and I'm ready to start looking into it, but before I want to have a 2nd opinion. The roof of my garage (floor in the attic) is made of 2x12s spanning 25ft. and they are on 12" centers. On one end they sit on top of the wall coming into the house from the garage, on the other they sit above the garage door and walk in door from outside. I cant see it but surly there is a huge beam going across the door to support the floor upstairs. Here is a rough drawing that I did in paint to show you guys how it is laid out. Let me know if you think that the structure is sufficient enough to support a 2nd level.