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I am building what is referred to as an ADU (Accessory Dwelling Unit), and will be required to install a 1-hour firewall which I understand to be a 2x4 wall with 5/8" gypsum on both sides. It must go from the concrete slab to the roof substrate, and in this case that's easy as the other side is completely unfinished and it's only one story. Note: it's 1-hour because I own the whole house, it's not a townhome.

My question is whether I can treat the fire wall as an interior wall as long as I don't have any electrical fixtures or the like breaking it up. Thanks!

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  • What do you mean by "treat the fire wall as an interior wall"? Are you talking about putting finishes on it, and if so, what sort of finish? (Paint? Wallpaper? Some sort of fancy faux finish?) Sep 13 '20 at 14:48
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    Is the wall part of a habitable room if it is receptacles are required every 12’ or no point more than 6’ from a receptacle. Residential homes with attached garages have fire walls and those have receptacles. I am wondering what you mean by finish? See NEC 300.21 I use metal boxes to maintain fire integrity.
    – Ed Beal
    Sep 13 '20 at 14:50
  • Oliver, note that the firewall doesn't need to be on both sides, both 5/8" sheets can be on one side. That may simplify things. @EdBeal Nothing says those receps can't be surface mount, but I like the idea of metal boxes. Sep 13 '20 at 15:22
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    True they can be surface mount if receptacles on both sides they can’t be in the same stud bay.
    – Ed Beal
    Sep 13 '20 at 15:37
  • So what I'm deriving from all this is: metal boxes, OK inside the firewall, and at least one in there somewhere if the wall is longer than 12' (i.e. no point more than 6' away from a recep) Sep 14 '20 at 19:58

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