How much weight a concrete flat roof can hold?

Question

Hi:

I'm a landscape design student. I have a design project for designing and building a green roof. I live in Puerto Rico, most houses are made with concrete, and the roofing is flat. How do I figure out how much weight can a flat roof can hold? A simple extensive Green Roof weighs between 60-150 kg/m2 (13.0-30.0 lb/sq.ft.) depending on the thickness of the Green Roof system build-up. How do I know if the roof is suitable for a green roof. The roof measures 50' x 60', about 8" thick, all concrete (with steel bars).

What else I need to know to figure this out? I mean calculations, formulas, stuff like that. Can someone please help? I'm quite worried. The teacher has been awful, he's no help at all. I barely have two week to finish this (plus my other classes). I have been doing searches on line with no luck. I don't need to hire an structural engineer, I just the know how, in simple words since I'm not an engineering student.

Any reference to anything (books, internet) will be greatly appreciated. Thanks! :o)

Answer 1

8 inches is quite thick. The load bearing capacity depends on the thickness of the steel reinforcing in it as concrete does not perform fails under tensile load and the roof gets it's strength from the steel.



Does the weight of your green roof include the weight of water when it is soaking wet from rain? At 150kg per m2 it gives 1350 kg over an area 3 x 3 metres.When you add the weight of water, that is a heavy load.



Consider reducing the thickness of your green roof where there is no wall support underneath and make planter boxes for extra depth which would be located over load bearing walls. Speak to your local council, they have friendly engineers that might be able to give you an idea of the load bearing capacity of the roof.

Answer 2

If your span is 12'x13 and the joist which I think is what you are referring to as studs are 2' apart I wouldn't plan on doing much out there. The 2 foot centers and only 2x6's and concrete pavers? Bad, bad idea? I would say if you absolutely have to have it and your mind is made up the only way that you will have half a chance is find the middle and put a beam to help hold the weight. But still I don't like the 12 feet x 13feet with 2x6 joist on 24" centers. If they were 2x12's maybe 10's on 16" centers you might be able to get away putting concrete pavers on it. I wouldn't but you probably can. With 10's you will get a bounce. I would say DON"T DO IT.

Answer 3

Does the roof need to be entirely flat or in Puerto Rico can you kind of bend the rules? I took a class and did a project on green roofs, I do know that your span of your roof is going to effect the weight of your system on it. Good Luck, try some of these sites:

Answer 4

concrete is very strong and hard in world there are so many megastructures build up of concret having large masses can hold the pressure but thickness of the concrete must be more