Anchoring to GWB over Metal Studs

[steris]

Hi All -

My company manufactures equipment needs to go between two rooms while maintaining an airtight seal between them. Typically we accomplished this using drop in anchors in block or cast wall or lag screws in wooden stud walls to compress. These screws/anchors would be used to compress a rubber gasket against the wall tightly to achieve a secure seal. We have been running into issues as our customers are using metal stud walls more and more. Dry wall screws and sheet metal screws do not provide the clamping force we need to compress the rubber gasket. On our normal configurations we typically use 3/8"-16 screws every 6" on center and tighten down to ~50ft/lbs. Is there any good way to achieve this level of torque/fastener size on metal studs? I've looked into toggle bolts but haven't found anything decent. Any help would be greatly appreciated! Sorry if this isn't completely relevant to this forum.

Thanks for the help!

Best,
Steris

 

[dhengr]

Steris:
You don’t say if you are screwing your equip. flange and rubber gasket to the flange or the web of the cold formed stl. stud. So, the exact detail will vary slightly depending on which it is. I think you have to be able open up the wall on one side or the other so you can get at the jamb studs and the header framing. On the flange or the web, install a piece of .125 x 1.5" bar stock, or some such, into which you torque your self tapping screws. You may have to clamp things together or buck this at each screw location during the screwing operation. If part of the problem is that the stud flange or web are too flexible btwn. each screw to achieve a tight seal, reduce the spacing to 4" o/c. Or put another stiffening element, light gage member on the stud, and then the bar stock inside that, to stiffen the stud surface locally. For example, if you used a 1.25x1.25x.125" angle for the stiffener you would accomplish both stiffening functions.

 

[steris]

Thanks for the response. We would be screwing to the flange of the stud. Your idea is good one but I failed to mention that opening up the walls is not an option for a variety of reasons. I did find toggle bolts that could work -

http://www.toggler.com/products/snaptoggle/overview.php

but I'm not sure if they are appropriate for our need.

I don't have much experience in construction or architecture - how are solid connections made to metal studs? What are the other options in lieu of customizing the wall? Any help would be greatly appreciated!

Best,
Steris

 

[dhengr]

Steris:
Maybe you need a softer, more easily compressible gasket, and a slightly closer screw spacing to accomplish your air tight seal. Toggle bolts are a possible solution, but they are a pain in the butt to install. There are some blind rivet and bolting systems out there. Maybe you have to pre-compress the system a bit at each bolting point, apply the bolt/rivet/screw, then release the pre-compression force, and go to the next hole. You probably just have to do some experimenting, in your own shop, with each gasket and bolting system you select. Easy and clean installation should win the day in your final selection of gasket and bolt/rivet/screw system. A larger dia. screw might accomplish what you want. It will give you a larger max. tensile force per screw in the same steel gage of stud. The gage of the studs can vary, bldg. to bldg., so go to a Big Box Store and buy the lightest gage studs to test. They will give you the lowest tensile strength connection and least stiffness btwn. connections. Now start increasing screw dia. and/or reducing screw spacing until you get the gasket compression you want. It’s the tension in the screw which does this, although the easiest way for you to finally measure this at installation is with a torque setting on your screw gun.

 

[rb1957]

do you need an airtight seal ? or a seal against pressure (is there a vaccuum in the rooms) ?

you say opening up the walls is not an option. does that mean you can't place a retainer strip on the far side of the wall and bolt through to it ? could you bolt a reinforcing plate to the near side of the wall, picking up on several studs at several places (distributing the seal load across more of the wall with "cheap-ass" toggle bolts) and seal against the plate ? how about using blind "pop" rivets (see Cheery, Huck) instead of toggle bolts?