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Old 03-11-2010, 12:51 PM   #1
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Firewall Box


Is it ok to cut a small hole in a garage OSB firewall to feed wires into an electrical box?

Do they make firewall rated cut-in boxes?

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Old 03-11-2010, 09:21 PM   #2
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I think if you have osb, you really do not have a firewall.
I thought firewalls were sheetrock.

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Old 03-11-2010, 09:41 PM   #3
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Originally Posted by jbfan View Post
I think if you have osb, you really do not have a firewall.
I thought firewalls were sheetrock.
as I understand, there is fire rated OSB but if this isn't fire rated, I do not believe it carries any fire rating at all.


and btw: the blue plastic electrical boxes carry a 2 hour fire rating. Not sure if the others have the same but I suspect they do.
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Old 03-11-2010, 11:28 PM   #4
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Agreed, if your wall is OSB on studs with no sheetrock underneath, it is not a fire membrane. The code doesn't permit the use of fire retardant treated wood panels for use as a fire membrane in a garage.

As NAP said, nearly all plastic boxes carry a 2 hour rating, which is more than adequate for the 20 minute required separation between the garage and dwelling. Look inside the box you want to use...In the fine print molded into the plastic it should say 2hr.

The building code does limit rated penetrations of firewalls (boxes) to be 16 square inches or smaller holes (2 gang) unless a larger box is specifically listed for use in a fire assembly.
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Old 03-12-2010, 07:25 AM   #5
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You may penetrate a fire wall on one side as long as there are no penetrations on the other side within 24" or they are separated by a stud or by using putty pads.
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Old 03-12-2010, 09:34 AM   #6
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Thanks for the input guys. The wall has OSB over the studs, then 5/8" sheetrock over that. The wall separates the garage from the house. I wanted to run a 12-2 cable from the attic and tap into a recepticle on the wall and figured I may have to cut a small hole above the electrical box in order to feed the cable into the box. If I did this, would I be okay with just patching the drywall, or would I have to patch the OSB as well?
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Old 03-22-2010, 02:31 AM   #7
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Originally Posted by mopowers View Post
Thanks for the input guys. The wall has OSB over the studs, then 5/8" sheetrock over that. The wall separates the garage from the house. I wanted to run a 12-2 cable from the attic and tap into a recepticle on the wall and figured I may have to cut a small hole above the electrical box in order to feed the cable into the box. If I did this, would I be okay with just patching the drywall, or would I have to patch the OSB as well?
Is your question, in part, whether the OSB is part of a fire rated wall assembly? http://osbguide.tecotested.com/pdfs/en/tb117.pdf

Note that this discusses the use of structural OSB as a substitute for structural plywood. I believe that is what you have. Fire rated OSB, and there is such a thing, is something different.
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Old 03-22-2010, 10:02 PM   #8
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I was just wondering if I had to patch any holes in the OSB used to fish wires through. I ended up just patching the sheetrock over the top without patching the OSB. No one will ever know. I don't believe the OSB is part of the fire membrane.

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