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I have started some work with a contractor to replace a roof on a terrace. They have removed the existing roof, and have left apparent some metallic bars placed on top of pillars. It feels sturdy in the sense that a 70 kg man can pull himself by the arms grabbing the metal bar, and it does not break (it bends ever so slightly).

For various reasons, I have started to lose confidence in the contractor. I worry about his competence. I am not sure I should cut the project now (which would be painful financially and would create conflict).

So I feel I need to educate myself on how to make a tile roof, to make sure I can watch what he does.

Three questions in total, but I am grateful for any advice, any partial answer:

  1. How can I make sure that the metallic bars will indeed support the weight of the tiles, plus the weight of the drywall he will put below?

  2. What minimum slope do the metal bars need to have?

  3. What other advice do you have for me, to watch out for in that situation?

Photo of the tiles he bought is below.

Metalic bars 1

Metalic bars 2

enter image description here

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    The answer to question number 1 is for a Registered and Licensed Professional Engineer whose field of practice is structural engineering. But to my eye from your photo it doesn't look like it will handle a tile roof. But I'm just guessing.
    – jwh20
    Dec 10, 2020 at 18:11
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    Ok, I will remove question 3. Thank you
    – DevShark
    Dec 10, 2020 at 18:14
  • Agree fully with @jwh20 on the SE. I'm not sure what kind of roof used to be on those metal rafters, but tile is heavy. Like, really heavy. Get someone competent & licensed to look at it or risk having the whole thing come down, potentially on someone's head.
    – FreeMan
    Dec 10, 2020 at 19:20

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Your roof system is not appropriate for several reasons: 1) required slope, 2) structurally inadequate

  1. The IRC Building Code requires a minimum slope of 2.5:12 for tile roofs. Your roof appears to be about 1:12. The tiles will need to be installed in what is called a “low slope application”, which includes plywood with a double layer of underlayment, which adds to the weight.

  2. The loading your roof must support is tiles = 6 to 10 lbs. per square foot (psf) depending on the tile + 2 layers underlayment = 1 psf + plywood = 1 1/2 to 2 1/2 psf depending on the thickness + joists = 1 1/2 to 2 psf + drywall on ceiling = 2 1/2 psf for a total dead load of 11 1/2 psf to 15 psf PLUS a live load of 20 psf to 30 psf for a total load of 31 1/2 psf to 45 psf. That is extremely high for a roof.

The current structure could only support a total load of about 5 psf based on my experience. (I don’t have calculations to prove my statement.)

In addition, the structure must support a wind load and an uplift force, which depending where you are , that structure is not adequate.

Get a Building Permit and the inspector will reject it for you.

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  • Excellent point about the permit!
    – FreeMan
    Dec 11, 2020 at 13:32

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