# Furred Wood Floor Joists Over Concrete Slab?



## fj80 (Nov 11, 2016)

My firm is designing the renovation of an existing 2-story warehouse into an apartment building, including the addition of a new third floor. Construction Type is II-B. 

We don't want the plumbing from the new third floor residential units to penetrate through the existing roof slab (which will become the floor of the third level) so I've been asked to add what is essentially a furred floor on top of the concrete slab, to run the plumbing through and then bring the lines down in a couple areas near columns.

My questions is: what type of furred floor construction is best here? Can you use wood 2x- floor joists? Does the code speak to this anywhere?


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## fatboy (Nov 11, 2016)

I don't see anything in 603.1 that would allow wood floor construction, other than the finished floor itself.


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## mark handler (Nov 11, 2016)

Change building construction types.
Wood framing above a concrete substructure is done all the time.
Think parking structures with condos above.


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## steveray (Nov 14, 2016)

I think there is a section for allowing "sleepers"....#7 maybe....Changing construction type is not an option unless you have a "horizontal firewall or whatever we call it...


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## mark handler (Nov 14, 2016)

steveray said:


> I think there is a section for allowing "sleepers"....#7 maybe....Changing construction type is not an option unless you have a "horizontal firewall or whatever we call it...


Depending on the thickness, the *"concrete slab"* should qualify as the *"horizontal firewall or whatever...".*


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## TheCommish (Nov 14, 2016)

2009 IBC

717.2.7 Concealed sleeper spaces. Where wood sleepers
are used for laying wood flooring on masonry or concrete
fire-resistance-rated floors, the space between the floor slab
and the underside of the wood flooring shall be filled with an
approved material to resist the free passage of flame and
products of combustion or fire blocked in such a manner that
there will be no open spaces under the flooring that will
exceed 100 square feet (9.3 m2) in area and such space shall
be filled solidly under permanent partitions so that there is
no communication under the flooring between adjoining
rooms.
Exceptions:
1. Fire blocking is not required for slab-on-grade
floors in gymnasiums.

2. Fireblocking is required only at the juncture of
each alternate lane and at the ends of each lane in a
bowling facility.
717.3 Draftstopping in floors. In combustible construction,
draftstopping shall be installed to subdivide floor/ceiling
assemblies in the locations prescribed in Sections 717.3.2
through 717.3.3.


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## Examiner (Nov 15, 2016)

I do not know how you can obtain a horizontal firewall on an existing building.  The entire floor or roof structure has to be designed as such not just the existing roof deck.  The existing roof deck/slab could be lightweight concrete with an insulation value which is not concrete or some other decking material that is not concrete for a Type II-B.  You need to see if the building can be another Construction Type.  As for sleepers I do not think joist will be considered a sleeper in the vertical long dimension.  What you have is a Change of Occupancy for the existing building which may help you if you go to Chapter 34.  You will be a Level 3 due to the occupancy change.


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## fj80 (Dec 12, 2016)

If I used metal floor joists, such as ClarkDietrich's C-Joist (see link below), sitting on top of the existing slab, I believe I would not need to change construction types, right?

http://www.clarkdietrich.com/products/standard-joist-system-accessories/c-joist


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## steveray (Dec 12, 2016)

You can use wood sleepers....
7. Finished flooring applied directly to the floor slab or to  wood sleepers that are firestopped in accordance with
Section 717.2.7.

Or the metal would be better....


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## fj80 (Dec 12, 2016)

steveray said:


> You can use wood sleepers....
> 7. Finished flooring applied directly to the floor slab or to  wood sleepers that are firestopped in accordance with
> Section 717.2.7.
> 
> Or the metal would be better....


Do you mean 718.2.7?


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## fj80 (Dec 12, 2016)

I'm not sure that the plan reviewer would consider 2x12's on edge to be sleepers. I tend to think of sleepers as running the long side horizontal...


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## ADAguy (Dec 12, 2016)

Metal best, fire, water and termite resistant.


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## steveray (Dec 12, 2016)

If it is touching the floor it is a sleeper IMO...As soon as it is elevated, it is a joist...


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## fj80 (Jan 3, 2017)

We've decided to use metal floor joists as sleepers for the built up floor. In this case do we need to provide fire blocking in the floor system between residential units? I would think we do, to stop fire and smoke from spreading under the floor from one unit to another. Which code section would address this with metal sleepers?


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## steveray (Jan 3, 2017)

The fire partition would have to meet the requirements of 708? for continuity...If the sleepers are part of the rated assembly, it might not need anything or just blocking...


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## fj80 (Jan 3, 2017)

Is there any significant advantage to running plumbing lines in a furred floor above the concrete slab, as opposed to core drilling and running lines underneath the slab? I've only seen it done the latter way, but my boss doesn't like the idea of plumbing lines running along the ceiling and the potential noise they'll make. But in my opinion, putting them in a furred floor makes them very hard to access for leaks or other maintenance work. Any opinions are much appreciated.


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## CityKin (Jan 3, 2017)

I agree with you.  I've never seen plumbing run above a slab as you describe.  The stack should be core-drilled and run horizontal under the slab.  Repair for a leak under the furred floor would be a nightmare, especially because the water could travel a long way away from the cause of the leak before dripping down through the slab.  

I would run the horizontal plumbing above the drywall ceiling but below the slab.


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## fj80 (Jan 3, 2017)

I was successful in my argument for running the plumbing under the slab rather than in a furred floor. A furred floor also adds a ton of extra cost, and the waste line noise concern can be eliminated by using case iron pipes on the verticals (but still PVC on all the horizontals) according to my MEP engineer.

Thanks for everyone's help. This is a great forum.


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## ADAguy (Jan 4, 2017)

Made greater by questions such as yours and the willingness to share experiences and observations.


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