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Most cost-effective fire wall?

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DwightB

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2006 IBC, existing 80' x 250' typical steel-framed building, with wood framed offices and mezzanine above. City had originally thought IIB construction until they learned of the wood construction that had been added inside. Now the owner wants to add another 80' x 150' and is way over square footage limits for VB construction and the city wants a fire wall. The owner wants to install 2 layers of sheetrock to the existing skin, then add a stud wall and 2 more layers of sheetrock on the new side of the studs, thus creating a 2 hour wall. Screws from the inside of the flanges could attach the sheetrock to the studs from the "inside" of the new stud wall and then the sheetrock would no longer be dependent upon support by the existing skin (ave ht 19'). The joints could be overlapped as required and taped, but the tape and finish would be on the inside face of the sheetrock. Is this "close enough" to UL to be acceptable, or is there a better option? Gotta be cheap.
 
twister2002: All of the installation instructions talk about fastening the gyp to the studs, even in one case, putting some gyp on one side, then installing on the other side, then returning to the first side to complete the attachment. Client wants to screw both layers to the sheet metal skin of the building (I calculate about 6,600 pounds), then building a stud wall adjacent to it and screwing at an angle into the flange from the outside and then into the 2 layers of gyp, thus "securing" it to the studs, but without a screw head to hold it to the stud. Taping the surface of the top layer is impossible because that layer is the one against the metal skin.

How about this option? Build the stud wall first, leaving a 4" gap between skin and studs. Then erect the new building with the structure having another 4" gap on the new side. Get the building weather-tight, then slip the 2 layers of gyp into the 4" gap on the new side to complete the 2 layers on that side. Then move to the old side, remove the skin from the inside (disassemble girts, cut screws as needed to dislodge the skin), and slip the 2 layers of gyp into the old side of the stud wall to complete the fire wall.

Is all of this trouble less expensive than an simple 6" block wall?
 
Does it have to have Structural independence????

Do not have the book

Or at least a tested assembly??

And what to do with penetrations?
 
Personally.....I think there is no "intent" to a lsted assembly...it is or is not.....I have seen equivalecies approved before...just not by me.....
 
The end wall in question is 16' at the eaves, 22' at the peak, 80' long. Is that too much to build using shaft wall techniques?
 
I don't see how a shafwall could have structural independence from either side if the other burns down.
 
The cmu wall most likely would need a footing below the slab at 19ft.

But I have a question why is'nt there a design professional making the options available?

pc1
 
Check my profile. I am the design professional, looking for the best option. I thought this forum was open to architects, not just building inspectors. Sorry if I intruded.
 
one problem is we are talking on words, with out some type of plan sometimes hard to make a call.

I would be looking first to a UL or other approved wall design, than try to fit it to the building.

do you have tested assemblies with some of the proposals you are trying to use?????
 
Sorry, Dwight no intrusion at all, you are correct this is not only for inspectors. Good luck with this project.
 
Dwight I guess where are you getting the design for the rated wall is it UL, some other approved lab, or chapter 721 IBC????

if you reference that,, the ones with more knowledge than me can give you a better answer
 
Gold Bond says their H-Stud Area Separation Wall can go up to 66' high. http://www.nationalgypsum.com/products/Product.aspx?ProductID=2390

Steel H-Stud framing members are attached on each side to adjacent framing with breakaway, heat softenable aluminum ASW Clips for lateral stability. I'm not sure if they can be screwed to the existing metal skin before the wall is built (the most common application is between stud walls of adjoining residences). Most gypsum board manufacturers offer similar assemblies.
 
U425 is the owner's choice. But one side is an existing building. With weather and security issues, the owner is asking that I specify the two layers of gyp on the existing side be attached originally to the skin of his building, then erect the stud wall, then somehow put in the required screws to the studs. It seems to me that the primary support for the gyp would be the skin and if a fire was on that side, the skin and gyp would fall, leaving the studs of my fire wall exposed. Another way would be to leave enough space between the red iron to allow a 4" or more gap between red iron and fire wall studs. Then, after the building is weatherproof, remove the existing skin and add gyp in the proper sequence working through the original steel structure (girts and columns of the end wall), adding the 2 layers of gyp and taping the outer layer.
 
I'll throw this out for consideration...have you thought about Type IIIB? Only the exterior bearing walls would have to be rated, so if there are no exterior bearing walls, then nothing would have to be rated. It would increase your allowable square footage so that perhaps this whole issue with the rated wall would go away.
 
Paul, U347 shows fire from one side, so the Gold Bond detail shows framing on both sides, essentially giving the rating for each side correctly but using only 2 layers of gyp. In the UL book and the Gold Bond book, both are called "area separation" walls. The code requires my installation to be a "fire wall".
 
CodeGeek, great suggestion. I think the city official was wrong when she said the existing is VB. I believe it and the new will qualify as IIIB and meets the area limits.
 
DwightB said:
I don't see how a shafwall could have structural independence from either side if the other burns down.
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Wrong.... a firewall only has to allow the construction on one side to fail without affect the other side....... A 2 hour shaft wall with aluminum clips tied into both support end walls would qualify as a firewall in the terms of the IBC -----

The strucutral independence went out the window with the old standard code unless the stae or your muunicipality amended the IBC.

FIRE WALL. A fire-resistance-rated wall having protected openings, which restricts the spread of fire and extends continuously from the foundation to or through the roof, with sufficient structural stability under fire conditions to allow collapse of construction on either side without collapse of the wall.
 
syarn said:
the exterior walls still need to be rated unless the building is more than 30 feet away on all sides from an other structures right???table 602
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You are correct. If the wall is greater than ten feet but less than thirty feet to the property line than the exterior walls must be at least one hour.
 
DwightB said:
2006 IBC, existing 80' x 250' typical steel-framed building, with wood framed offices and mezzanine above. City had originally thought IIB construction until they learned of the wood construction that had been added inside. Now the owner wants to add another 80' x 150' and is way over square footage limits for VB construction and the city wants a fire wall. The owner wants to install 2 layers of sheetrock to the existing skin, then add a stud wall and 2 more layers of sheetrock on the new side of the studs, thus creating a 2 hour wall. Screws from the inside of the flanges could attach the sheetrock to the studs from the "inside" of the new stud wall and then the sheetrock would no longer be dependent upon support by the existing skin (ave ht 19'). The joints could be overlapped as required and taped, but the tape and finish would be on the inside face of the sheetrock. Is this "close enough" to UL to be acceptable, or is there a better option? Gotta be cheap.
Click to expand...
What makes it VB rather than IIIB?
 
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