This is a commercial job. Building is being divided because new tenant doesn’t want to rent the whole thing.
So a 100′ firewall is required between the two spaces. For about sixty of those feet stands an existing wall. It has 1/2″ drywall hung on the horizontal. Engineer says this must be covered with another layer of 1/2″ drywall hung on the vertical.
Well, I played around with this a bit. What a pain. The studs are covered and so hard to locate. And just for the fun of it, they are not spaced quite right. So I end up with board that has an edge that is not over a stud.
So it occurs to me that if I glue the second layer to the first, then it won’t matter if I’m “missing” a stud or two….
What kind of glue does one use here? And does it comprimise the fire rating??
And it also occurs to me….I am under the impression that well hung drywall does not sit on the floor, but is 1/4″ or 1/2″ or so above the floor. Doesn’t this compromise the firewall??
I’d ask the engineer, but he isn’t very definitive with his answers (not what I thought I would be getting…).
Thanks.
BTW…Originally the city was going to insist on a three hour wall with the existing wall torn down and the entire thing built with steel studs, etc. The owner didn’t want to go to that expense and stressed how the other side was vacant. The city compromised with the existing wall upgraded to a one hour rating and the forty feet of new wall built to a three hour rating. That is with the understanding that if a future tenant occupies the other side of the building, then the one hour wall will have to come down and a three hour built.
The owner likes the compromise because he is hoping that the new tenant will exercise his option to buy in six months and the problem will be his.
Someday (after I finish the roll of film and get it developed) I’ll post some pics of the trusses in this place, especially the one with the sag!!!
Rich Beckman
Another day, another tool.
Replies
I went through a similar routine over a year ago. Man, you start thinking you know building codes, go dig into commercial work. Yeah, now I think it was foolhardy, but at the time it seemed like a good idea. What I gleaned, for whatever it may be worth . . .
On the adhesive, you better ask. It seems silly, but I think most of us would assume drywall adhesive would be fine. You never know. The fire code to me seemed to be fairly convoluted and difficult to interpret. Barring that, screw it and hit your studs. Even if you leave edges running wild with the adhesive, you need something to hold them until it sets, whether that's drywall adhesive or durabond.
Yes, the gap at the floor seems foolish; here you can't do it. EVERY gap has to be filled. Around pipes and HVAC, intumescent fire stop caulking. Where the DW hits the girders, if you're going above the grid ceiling, it has to be taped and mudded. I prefer to make the ceiling one unit and run all the partitions up to it. Solves multitudes of problems with the various services running overhead. The down side is you could end up with uneven tiles in the rooms. Oh well.
Get your variance in writing, stamped, signed, part of the plan package. I'd get told one thing by one inspector and the fire inspector would sing a different tune.
Naw, commercial work - there's lots of guys more savvy in that. I think that job convinced me that branching out wasn't necessarily a good thing for someone with the residential mentality. But theres certainly money in it.
"The child is grown / The dream is gone / And I have become / Comfortably numb " lyrics by Roger Waters
There are rock to rock SR screws, Hyper course and very deep threads.
Suppose DW glue would work or rip the sheet to fit...
Who ever invented work didn't know how to fish....
I'm sure you can leave the end of the boards off the studs, but better ask the inspector first. On these firewalls, the code calls for the end to stay on the stud. If the inspector allows you to leave it off the stud, do this:
- Get a can of spray adhesive and spray the first board and the 2nd board end real good about 6 inches at the end. Get cement board screws in 1 5/8", these screws are grey looking and available at HD and Lowes. These screws are the only ones that indent into the drywall. Once the spray adhesive dries it's solid. Make sure the screws are 1 5/8" and not 1 1/4" as the longer is needed for 2 layers of 5/8".
If you need to hang on studs get a stud finder at HD or Lowes and mark them before you hang the 2nd board.
Edited 2/15/2004 6:40:27 AM ET by Zano
That is with the understanding that if a future tenant occupies the other side of the building, then the one hour wall will have to come down and a three hour built.
So your client is essentially a moron, then. He's going to pay you to bring the existing wall up to a one-hour rating while the space is empty, and then pay someone else later to rip that all down and build the proper wall while someone's occupying the space....
Well, anyway- the only way to CYA on that fire wall is to ask the engineer to provide you with the UL assembly # that he wants you to follow. Get a copy of the diagram and spec for that wall, and follow it to the letter. It'll specify how to breal the drywall joints, what type and length of screws to use, and what sealants are required at the floor and ceiling.
I'm suprised the inspector's letting you use 1/2" rock- most commercial work is all 5/8", and one layer on each side gives you the one-hour rating you're looking for. I'm also suprised taht there's a 3-hour rating required between tenants- are these retail stores, office tenants, or explosives manufacturers??
Bob
A fire rate 1/2" dw is available in my area, special order.
Dave
"So your client is essentially a moron, then. He's going to pay you to bring the existing wall up to a one-hour rating while the space is empty, and then pay someone else later to rip that all down and build the proper wall while someone's occupying the space..."
No. He's a gambler. He is gambling that the tenant moving in will exercise his option to buy the building, and that no tenant's will show up for the other half before then. That way, someone else will pay to tear that wall down. The real waste here is that the exiting wall we are saving is only 9 feet tall. We will be building a wall on top of it to get to the roof (another 9 feet or so) that will need to be torn down if and when the day comes.
At least I see that my instincts on this were correct. I guess I'll cut the sheets to fit the studs.
Thanks.
Rich Beckman
Another day, another tool.
rich .. couple things .. at the risk of repeating..
get a stud finder and a crayon... find 'em and test em with a nail.... mark all your studs
get the ul assembly the engineer wants to conform to the city requirements.. put that in your permanent file..
if it calls for 1/2 gypsum.. fine... if it calls for 1/2' firecode... use it..
if it calls for 5/8' firecode use that.. every assembly has a materials and methods spec. or it will not qualify for the one hour rating..
you may be able to use glue.. maybe not... i'd use PL 200... but liquid nails is good .. and so are many others.. they will say " for gypsum panels"..
you will need longer screws..
if the assembly doesn't require you to land on studs .. then don't..but make sure you know where the studs are..
if you get to use the glue.. you can cut back on your screw schedule.. as long as you comply with the UL or FM spec the engineer should give you
Mike Smith Rhode Island : Design / Build / Repair / Restore
There's lots of misunderstanding of how the details of fire walls are worked out. They're not just thrown together in a hunch. Fire walls are designed by building actual walls and subjecting them to fires under specified laboratory conditions. If a wall performs to a certain standard for a certain period of time, it earns a rating.
Since walls are tested and rated as an assembly, altering any detail of the assembly voids the rating. That's not to say that an alteration can't be effective, but without testing you can't say that it will or won't. That's why firewalls are always constructed to a specific set of construction details.
Lots of details in the code are there because they were learned tragically. They were not made up by some code jehu to annoy contractors and owners.
I suspect that adhesive would not be allowed, unless you can find an example of an assembly that used adhesive that held up to a real fire in a test.
I lived in towns with old fashioned dowtown storefronts. When a fire started in one, the whole block burned. Several times. Firewalls really do save money, livelihoods, and lives.
Rich, don't know if you started this, but I was under the assumption that you would have to stagger the seams from those in the original board hanging. Are you sure you have to change direction?
Remodeling Contractor just outside the Glass City.
Quittin' Time
"Are you sure you have to change direction?"
I'm sure that's what he told me. He did mention that the seams need to be staggered as well (by two feet), but determining where the existing seams are isn't exactly doable (well hung drywall!). I started one foot off the corner so that I'd have a better than even chance of staggering the joints by one foot.
Rich Beckman
Another day, another tool.
Rich,
the engineer is wrong about reversing direction of the boards. as long as all of the seams are staggered and the first layer is firetaped, the direction is meaningless. you can try G screws to attach the layers together, but they don't work their best with a 1/2" base. they tend to strip before countersinking.
a phone call to the engineer could save you a lot of trouble.
carpenter in transition
It is acceptable in many areas to stagger seams. What I always did was to just rip a board in half and start with it. It is better to do that on the first layer so that your seams are easier to finish on the second.
Rich,
I would get everything required of me on a blueprint and in writting in order to not be the one who is ultimately liable. If they don't specifically specify certain things, then I would use regular drywall adhesive. You can also use drywall mud. There are certain tools to help spread it. Also, they make a screw specifically for drywall to drywall aplications. We always called them laminators. They are very course threaded drywall screws. They were larger than the others. To put them in the drywall you usually have to take off the tip of the drywall screw gun and run them in at an angle. But they held.
Hope this helps.
A one hour fire wall here requires two layers of 5/8. The inspector has told me he doesnt care if its one layer on each side or both layers on one side. He also said that all 5/8 rock is now fire rated as opposed to the type x that was called for in the past. Im guessing you have to put up the second layer because the 1/2 is already installed. Direction shouldnt matter. We cant leave a gap or it has to be fire caulked, but inspectors here dont really nit pick me too much on things like that. I would talk to your inspector. Have all your questions ready and do a ten minute meeting with him, that seems to help me on jobs like that. He sees you want to do it right and is less likely to ride you about little things, unless he is a jerk to begin with, and I cant help you on that one.
It is my understanding that the proper technique for a double layer fire wall (according to fire codes) is that the second layer should be should be glued and screwed to the first
BUT ONLY with the Laminating screws tha some else here mentioned.
AND the screws should NOT be put into framing members.
The screws are to be backed out before taping
This prevented the heat of a fire on one side from igniting the paper on the other side Via the increased heat transfer of the screws.
I know it may sound like Hoooey, but like was said earlier these rules are based on lessons learned the hard way and from laboratory testing.
The rules may vary with wood vs. steel studs so check with your local authority.Mr T
Do not try this at home!
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We do this type work all the time. Got to Grabber or any good drywall supplier and ask for laminator screws. With them you screw board to board with no worrys about stud spacing.
I asked the engineer about the gap at the bottom and he said there should be a gap and that it should not be filled. His reasoning was that if there was water on the floor, you don't want it being wicked up into the drywall and compromising the fire rating.
He also said that the drywall to drywall screws would be fine as long as there were just a couple of spots.
BUT SINCE THEN:
Today comes word that the city building inspector is no longer requiring a firewall of any kind. Any wall that we want to put up is acceptable!!
Story: Building owner was on the line for $10,000 of renovations. Anything over $10,000 was to be the responsiblilty of the tenant. Well, once it became clear that the 10 grand would pretty much cover everything EXCEPT the firewall and that the fire wall was going to cost a LOT (100 feet, 18 feet high, 6 large trusses to wrap, large numbers of other stuff in the way ), the tenant went to the city buillding inspector and talked her out of the firewall.
The tenant told me that he simply explained that he might very well be expanding into the other space and that the other side was vacant.
I figured he simply said something along the lines of "Do you want me to open my store in your town or not??"
I heard that he told someone else that "Building inspector exist to discourage businesses from openning"
Rich Beckman
Another day, another tool.
Edited 2/18/2004 10:27:30 PM ET by Rich Beckman