Turning a flat roof into a deck?

If you take a look at this picture:
http://img.villagephotos.com/p/2005-10/1090906/exterior.jpg
This house has a flat roof. The current owner uses drop ceiling in many places so that he can route wiring, AC ducts and electrical and lighting outlets through the roof. I don't like panelled drop ceiling so if I get this house I will be removing them.
Which means I will have to find another way to route wires and ducts on top. The roof has very little room a few inches with insulation that's all. The second story on the left side actually has an exterior door where it opens and one can walk on top of the flat roof.
What I am wondering is how easy will it be to build a new flat roof on top of the existing flat roof (but elevated 24" or so higher) so we can use that room to route wires and ducts. Then I can cover the roof with flooring material (tiles or slates?) and put railings around it's perimeter so the roof becomes a sun deck.
Will this be a prohibitively expensive project to do? How would I determine if I can put new flooring on the roof - whether it was designed to take this added weight or for someone to walk on? Any other ideas?
I know this is probably more a question for a contractor, but this is a house I plan on putting an offer on and I need to get as much information as possible about what can and cannot be done.
Thanks in advance,
MC
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Too much change for just a cosmetic concern. Find a house you like better and spend your money and efforts on something you will enjoy and will pay back big like a fancy bathroom or a really nice kitchen.
Sounds like it would cost every bit as much as tearing the roof off and building a new one from scratch. It can be done but it is a major renovation for modist gain. Might as well raise it 8 feet, the extra cost of lumber for the walls might not be such an add on but the extra SF added to the house would push the permit price significantly higher and result in a major tax reassessment.
The load carrying ability of a flat roof is largely determined by the size of the joists and the span they need to cross. Normally a roof only carries a static load, so to stabalize it for a dynamic load like people walking (so it does not wiggle or make too much noise in the house) would require additional bracing and stronger decking than normal.

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With a careful design - one that pays attention to high winds, flashing, drainage, and load paths - it might be done. The problem is one for a really careful contractor or IMHO for a thoughtful architect. The new roof surface will be higher than the existing roof surface and so access to it has to be considered. Code requirements and documentation for a building permit are additional considerations. TB
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wrote:

This does not follow. If you have the available headroom, you could just as easily take down the drop-ceiling, and build a sheetrock ceiling at the same height.
But if you want to make the roof walkable, don't like the ceiling, and hate the mis-named "mansard" bit, then by the time you fix everything peicemeal, you'll be better off just taking the whole roof off and building what you want.
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evidence of old water leaks. The drop ceiling, and the exterior door opening from second floor, tell me there likely was a deck up there (probably just planks on sleepers), and the original hot-mop roof started leaking under the sleepers. Did house have central a/c when built, or wall units? House looks early 1960s, so wiring would have been minimal by modern standards, and if it was an beam-and-T&G ceiling, any hanging lights would likely have been fed by raceway, or a notch on the top of the beam, or possible box-section faux beams. To replace the the tiles, you can always go to a high-velocity duct system, and fit it all in a 2x6 framing grid, covered with drywall, jammed up tight to the old ceiling.
But like the others said, you need a site survey by a qualified architect or engineer, to determine what is actually there, and what changes are realistically possible. Unless bidders are lining up, the seller shouldn't care about a non-destructive inspection.
aem sends...
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