Fire Wall Vertical Continuity Question

[Trillers]

We are working on a project which requires retrofitting to bring the building up to code.

This is a reinforced concrete and CMU building constructed by the U.S. Navy and consists of reinforced concrete footings, floor slab, columns, beams and roof. The walls are reinforced 8" CMU.
One of the issues for the retrofit is that we need to separate the 15,000 SF building into two "fire building" one consisting of 10,000 SF and the other 5,000 SF to qualify under the 12,000 SF max floor space allowed before sprinklers are required.
So here's the issue: The architect insists that the fire wall should penetrate both the 8" floor slab and the roof slab. Our position is that with the exceptions for continuity provided in IBC 706.5 and 706.6 the fire wall (6" CMU) can be placed directly on the floor slab and flush up against the roof slab.
Our opinion is that the exceptions apply in this case - the architect disagrees. The Fire Marshall says he is with me as long as I am willing to certify that it is a fire wall and not a fire-resistant wall.

Any one out there run across this issue before?

Thanks.

 

[dik]

Often used the firewall to the U/S of slab and building on top, If you need to transfer the load through the slab, it is necessary to drypack the last inch or so. Does the wall require grouting to achieve a ??? FRRf? Often need 4 hours. Can you core through the slab @ 2' or so to install through dowels to the wall above? and does the fire wall have to extend a couple of feet or so above the roof? Use 25M (#8) dowels due to their stiffness.

If not grouted and dowelled through, then it becomes an interesting problem of providing lateral support from both sides while a fire burns down the 'other side'.

Can use firestopping between the top of the wall and u/s of slab, but, I haven't used that approach for maybe a 4 hour wall...

Dik

 

[Trillers]

Hi dik/

I think I need to clarify - the configuration is the wall will sit on the 8" slab on grade and terminate at the roof slab above. This is a one-story building so structurally adjoining to adjacent floors is not applicable.

The floor slab is only 8" thick - the fire wall will be structurally stable even in case of fire since it will be attached along a main column grid which, if collapsed will take down the entire building.

My particular concern is if the wall connecting to the slab on grade by dowels will conform to the exceptions without breaking through the slab to create an integrated fire wall. I believe it does but hoping for some insight and additional thoughts if you have run into this issue before.

Thanks.

 

[dik]

8" thick conc slab will likely give you a 4 hour rating and there should be no requirement for improvement, and I've never heard of a slab on grade requiring any FRR. The masonry wall can be constructed on it, with or without nominal dowels, but, if a firewall, then it may not have the required performance... depends on the CMU, but, it may not provide 4 hours; I don't know what you require... The biggest issues will be the roof penetration and the projection beyond the front and rear walls to give you a proper separation... What is the roof construction? and what is the FRR required for the firewall... how high above the roof does it have to project, if at all, and how far does the firewall have to extend beyond the existing building envelop? Can you provide a floor plan and a building section?

You can even construct the wall using shaft wall construction for an extended FRR. Check with UL assemblies to determine the wall construction.

Dik