enter image description hereI had recent water damage remediation done where a large portion of drywall was ripped out behind the fridge which has exposed a firewall, as well as an adjacent perpendicular wall and part of the ceiling above as well.

I'm not 100% sure but it seems as though it's 1/2" thick. Some parts it appears to be around 5/8". Should I stick with 1/2" drywall (moisture resistant as well?) for everything in this case? The unit above us that caused the damage has the same exact layout with the kitchen and fridge...

I have a length of leftover 1/2" drywall from another project and I was putting it up against the wall next to the portions that are cut-out, and it seems to fit the width. Of course, I don't have any 5/8" drywall to compare it to. I'm guessing the 5/8" would pop-out more.

The concern is if using 1/2" drywall over that firewall is not "up to code"

  • How is that firewall intended to be detailed? Can you get some sort of as-built drawing that shows a cross-section detail for the inter-unit firewalls in your building? – ThreePhaseEel Nov 6 '17 at 23:25
  • How do you mean? I don't have any drawings that would show a cross-section between units, etc. In the void space above the ceiling/beams the firewall does not appear to extend up into my neighbor's unit though, as far as I can tell. – Jeremy Nov 6 '17 at 23:51
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    well, the first question I'd have is "how do you know it's a firewall?" The OSB might indicate that it's a shearwall, or perhaps not. Certainly most firewalls don't stop and leave an open void space above them... – Ecnerwal Nov 7 '17 at 0:28
  • Thanks for the info. I overheard the water remediation guy say he ran into "firewall" when he was on the phone. In this case, if it's not a firewall, what would it be? Is it common to see another wall [of plywood] behind drywall when it comes to the kitchen area? – Jeremy Nov 7 '17 at 0:35
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    An interior plywood wall is probably a structural shear wall. Any thickness of drywall can be installed over it... – Lee Sam Nov 7 '17 at 0:49

I doubt if it’s a fire wall that would require 5/8” gypsum board. The only place I can think that 5/8” Type-X (fire rated) gyp board is required is on the garage side of a common wall with an attached garage or on the ceiling of 1-hour fire separation between units, or on a wall next to a furnace room or garbage room.

If any of the old gyp board is still around, you could look on the back and see if there are any fire ratings stamped on it. You could also look on the other side of the wall to see if a “Fire Rated” board is used on the other side of the wall.

There are “Fire Partitions “ required between units (or sleeping rooms), but that is for a building with 3 or more apartments and you could use 1/2” fire rated gyp board.

Remember, not all 1/2” or 5/8” gyp board is fire rated. If it’s a true fire wall (or fire partition) it must have a fire rated stamp on it and it needs to be applied on both sides of the wall, except between the garage and apartment.

There is a sound control rating required between units, but that does not require a fire rated board.

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