# Non-load-bearing walls under a ceiling/floor assembly... how?



## EnvisionMan (Feb 19, 2014)

Having a serious issue with designing an over/under duplex.  Side-by-side duplexes are a breeze, but this project is becoming a challenge.

We have selected a good 1-hour assembly for the ceiling/floor.  No problem.  We have also selected a good 1-hour wall assembly for the exterior walls.  No problem again. However, the builder does not want the interior, non-load-bearing walls to be fire-rated.  He wants to use 1/2" drywall and not worry about using all the fire-rated mechanical things (metal j-boxes, fire caulking, etc).

So how can you build a non-load-bearing, non-fire-rated wall under a fire-rated assembly?  There are serious issues when it comes time to actually constructing it.  The drywall (we are using a double layer of 1/2" drywall) cannot be broken for anything but a 1-hour fire wall.  But all the wiring in the ceiling/floor assembly has to be roughed in before the sheetrock is put in place.  But the non-load-bearing wall has to be installed UNDER the sheetrock.

See the problem?

In order to run a wire from the switch to the ceiling light, I have to have the wall in place.  But in order to have the wall in place, I have to have the sheetrock in place between the ceiling and wall.  But in order to install the wiring I can't have the sheetrock in place.

What gives?

:-(


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## JBI (Feb 19, 2014)

What gives is that you seem to be allowing a contractor to dictate design. Designers design, contractors follow the prepared plans. Draw the design to meet code and make sure the contractor follows the plan. Simple. :wink:


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## steveray (Feb 19, 2014)

Run staggerd joint drywall pieces first on the ceiling and frame to it.....


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## EnvisionMan (Feb 20, 2014)

So what JBI is saying is that all over/under duplexes have all interior walls as load-bearing, fire-rated assemblies?  I find that incredibly hard to believe.  I suppose it is possible, but not likely.  That means every single wall receptacle has to be fire-rated... every TV jack, phone jack, security panel, light switch, wall plug... all have to be fire rated j-boxes.

If that is what over/under duplexes require, I guess I will deliver that info to the contractor.  I would just hate to find out (or for him to find out) later that there was a much simpler way.

Steveray... we thought about attaching the drywall to the ceiling and putting the non-load-bearing wall below, but is there any restriction on how close the tape/float joints are in the ceiling?  We would end up with a LOT of extra joists around the perimeters of rooms.  Have you seen this done onsite?

Thanks, guys.


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## ICE (Feb 20, 2014)

Consider this: Two top plates is 3" of lumber.  What rating is 3" of lumber worth?  Then there are through penetrations for cable and pipe to deal with.  Hilti has the answer for that.


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## steveray (Feb 20, 2014)

The drywall assembly listing will tell you how far the joints need to be staggard...just like patching a hole in a fire rated assembly...


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## ICE (Feb 20, 2014)

Staggering joints is all about a hose stream test.  The joints are staggered from one side of a wall to the other side of the wall.  It is the horizontal seam that is staggered.

It's been a long time since I've dealt with rated construction so don't believe anything that I come up with.


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## mtlogcabin (Feb 25, 2014)

There are some exceptions. Look at Sections R302.4 through R302.4.2 and the exceptions


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## JBI (Feb 25, 2014)

EnvisionMan, That is not at all what I said. All I suggested was to stop letting contractors design.

IF the designer has a plan that he/she feels is code compliant, then that is what should be drawn and submitted for review.

That a particular contractor is unhappy with the design-of-choice should not be a deciding factor in how the building is designed.

Are you suggesting that there are absolutely no recognized one-hour floor/ceiling assemblies that allow simple mechanical penetrations?

If so, you need to take another look.

Most one-hour floor/ceiling assemblies make provisions for minor penetrations, especially membrane penetrations.


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