bump - add second floor?

Hi all, I've done a lot of remodeling, but have not built a home before, so before I get a contractor and start asking stupid questions I thought some of you might help.
I have a concrete block building with a flat roof. The roof is "sunk" below the top edge of the block wall. The top of the wall is capped wtih angled concrete blocks for water run-off. I'm thinking about building a home/apartment on top of this space. It's 20 feet wide, 40 feet long. Can I span the 20 feet with floor joists without supports underneath? Do I need to remove the angled concrete to create a flat surface to build on? How do I ensure the block walls are an acceptable foundation? Thanks, Greg
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Can I span the 20 feet with floor joists without supports underneath?
Yes, you are at or beyond the legitimate span of dimension lumber, but well within the limits of LVL and Trus Joist systems.
Do I need to remove the angled concrete to create a flat surface to build on.
Yes, I would assume you would want to remove the parapet walls or at least the sloped top units. Much of the decision will have to do with the wall material and exterior finish of the 2nd floor.
How do I ensure the block walls are an acceptable foundation?
If you have no original blueprints of the existing structure, you may be required to excavate to verify the depth and dimensions of the existing foundation. Footing dimensions are based on the bearing capacity of your soil, frost depth, and total load imposed. I would hire a structural engineer at this point, the local building inspection department will require it anyway. He will also need to determine header bearing capacities over any existing openings in the load bearing walls and sheer design to withstand the wind and racking loads imposed by the larger structure.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Keep the whole world singing. . . . DanG

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I have spent 35 years in the building trades and have only seen a few homes that would support a second floor. Call your building official and be honest.
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