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Wednesday, January 4, 2023
Question:
Hell Charlie! We are wiring a new building with a rooftop patio. The roof is metal corrugated material, with concrete on top for the patio/deck area, and exposed on the bottom, inside the building. I know that 300.4(E) generally does not permit this, but I cannot see how there is a potential for damage to the EMT if there is concrete on the top of the roof deck. My question is: Would it be code compliant in this installation, to install an EMT mounted directly to the bottom of a metal corrugated roof deck, without any gap or space between the metal roof and the EMT? Thanks, Tim Drake
A
Answer:
Tim, thanks for participating in the CQD. I see you submitted this question referencing the 2020 edition of the NEC®, as it makes a difference regarding this question and topic. Under the 2020 edition, the required spacing in Section 300.4(E) would be required. However, the 2023 NEC® has added an exception to Section 300.4(E) that states the following:
“Exception No.2: The 39mm (1 ½in.) spacing is not required where metal-corrugated sheet roof decking is covered with a minimum thickness of 50mm (2in.) concrete slab, measured from the top of the corrugated roofing.”
Under the 2023
NEC® your installation, if the concrete is at least 2” thick, you would not need the spacing. If your local jurisdiction is still on an earlier edition of the
NEC®, it may be worth contacting the local AHJ and discuss any possible options.