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I am certain that this has been answered, but I cannot seem to find an answer that is certain enough to give me comfort.
I am building a barn with metal truss frame, 2 x 8 purlins 2' on center supporting the roof. The initial plan was to have the metal roofing contractor screw the 5v metal roof directly on the purlins, then spray open cell foam directly on the metal roof. The walls will also be sprayed with open cell foam. The contractor I have chosen tells me he thinks I need to put 3/4" decking on roof so he can put felt under the metal to prevent sweating and eventual mold/mildew/corrosion of the underside of the metal. However, I have found dozens of web pages put up by industry experts that seem to say I will have no problem staying with my initial plan. (Contractor says he will do whatever I want, just advises against it based on his 22 yrs of experience) I may air condition the space but hoping that I get enough air motion to just use fans and ventilating exhaust fans to make bearable. I would certainly appreciate any advice you guys can provide. PS - I have to make a decision on this by Aug 11th. Thanks
If he is using closed cell foam, and does a good foaming job, there should not be issues with moisture reaching the back of the metal roofing and condensing, unless there is a roof leaking allowing water intrusion. That said, one down side to foaming direct on the metal is it creates a horribly difficult job if and when the roof ever needs to be replaced.
I also keep being told that even the exposed fasteners - heavy duty screws will back out occasionally. Is that really to be expected?
In all likelihood, yes, within 5 - 7 years they will need to be tightened and probably in years 12 - 15, you will want to replace the screws. In your case, you definitely do not want the screws to be allowing drips through the metal.
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