Duplex and 1 hour fire wall question

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cbe's picture
Duplex and 1 hour fire wall question
SoftPlan Version:
2016 Plus

The duplex will be 28' x about 60' long with the building split down the middle to make two 14'x60' units.  I know that I need a 1 hour fire wall separating them from the foundation to the bottom of the roof.  My question is: how do you brace the roof and ceiling if I can't penetrate the fire wall? Does anyone have any wall details they'd be willing to share?

- Cory

Lkelsey's picture
One Hour Fire Rating

Try the web site usgdesignstudio.com. It has lots of information about fire rated assemblies. You can contact their state rep also.

Hope this helps


L Kelsey

ChrisStewart's picture
Yes I had the same question a

Yes I had the same question a few years ago.

You can find lots of one hour rated wall designs but the joist connection is never mentioned. 

I was surprised because the code said it needs to be a tested assembly    -and that should include the ceiling and or floor connections as well.



You probably want to ask your local code official but in my area joists and floor decking are allowed to penetrate. 

cbe's picture
I asked a plan reviewer at

I asked a plan reviewer at the local permit office and they wouldn't give me an answer.   They basically said to use an approved method but wouldn't offer any information beyond that.  So I consulted with an engineer that gave me a detail he uses.  It doesn't transfer 100% to my project so I'm re-drawing it.  

I haven't finished it, but you can see it from the attached images.  Basically, it is a wall built with 2x6 plates (bottom and top), but 2x4 studs.  The studs are 12" o.c. but staggered so each side has a stud on 24"o.c.  Sitting on top of the top plates is a 2x6 on edge to the left and right side of the plate, then a another 2x6 plate on top of that.  This creates a header above the ceiling line.  With the 5/8" gyp board going from floor to the underside of the roof, I have another 2x6 on each side of the drywall bolted through the header.  This 2x6 header is more like a ledger board for the ceiling joists.  I'm using 2x6 ceiling joists or else the header and ledger would be made of whatever size joists I used.

The tricky part is venting the attic space.  I've never used off peak vents, but don't know of a better way to vent the attic without having a mechanical vent.