Metal Stud Bracing - Brick cavity wall

[RWW0002]

For a brick/metal stud cavity wall (veneer brick - 1" airspace - 2" rigid insulation - (exterior sheathing?) - metal stud - interior gyp.) curtain wall style construction.

Is it common practice anywhere to allow the architect to omit the exterior sheathing layer at the exterior face of stud and attach the rigid insulation directly to metal studs (provided brick ties are attached directly to metal studs)?

In the past I have required the exterior sheathing layer (densglass or similar) and attached brick ties either to or through that layer to metal studs beyond. I consider the studs to be braced continuously for this case and all wind loads transfer to the studs. I am currently working for a new client who wants to attach the rigid insulation directly to the face of stud. They have justified the waterproofing on their end.

What are the general thoughts about relying on the brick ties (acting through 2" insulation and airspace)/brick or rigid insulation itself to brace the exterior face of metal stud?

It also seems odd to me to not have a span-rated component other than the brick as part of the wall envelope. If the brick ties do not hold up and some brick fails (which I have seen happen from time to time) we have weather blowing directly into the building. On the other hand I guess this is not much different than many metal panel systems that attach directly to framing. This is just not standard construction for me and I am a little hesitant. Any literature available on the topic?

 

[jayrod12]

Brick ties as lateral braces? There is no way I would let that fly.

At a minimum, strap braces and bridging.

 

[RWW0002]

Bridging will be provided @ 4'-0" O.C. @ punchouts and attached to metal studs with clips, however I am still concerned about bracing the compression flange of the studs.

 

[rdubs]

Are you suggesting that the brick veneer can take the place of structural sheathing to restrain lateral forces on the building? I would be very nervous about doing that.

 

[XR250]

I have run into this. IMHO, it is a stupid system pushed by Dow on to Architects. You have to count on your bridging and interior sheetrock to brace the studs.
I feel that the interior and exterior sheathing provide the majority of bracing for metal stud wall and counting on the bridging is sketchy at best but I guess it is something we have to trust. Using a block and strap detail and then adding diagonal straps to that is a better, yet costlier system.

Between this new Dow system, the new anchoring limitations, crappy BIM drawings and inattentive and unreasonable EOR's I think I am going to quit the metal stud business.

 

[dik]

Don't do it... bad idea. There's no way you can justify this with calculations.

Dik

 

[RWW0002]

I agree. The system makes me nervous. After looking into it a little more there has been some testing of similar systems including thick rigid insulation (w/siding-not brick) and no sheathing, but what I have found is mostly concerning transfer of wind load through the insulation layer and concerns about fasteners carrying dead weight of finishes. Lateral bracing of flanges does not seem to be addressed.

I guess you could justify the use AISI C3.1.3 (Beams Having One Flange Through-Fastened to Deck or Sheathing) provisions and reduce the moment capacity accordingly, but that is relying on the interior gyp alot more than I am comfortable with - and you end up with a 50-65% reduction in moment strength. - I assume something like this is what you are referring to XR250

 

[XR250]

I have never seen that publication, but will check it out.
I think the solution is to require that they add the layer of gyp sheathing on the exterior below the foam.
This is why I dislike these jobs. By the time they hit my desk, I have no say in the matter and the owners are always trying to cut costs so convincing them to add a layer of gyp is futile.

 

[RWW0002]

Thanks XR. That is the direction I have tried to lead them. We may end up using a combination of light gage strap bracing, bridging, and interior gyp., but I am expecting pushback on $$.

 

[sandman21]

If you have proper bridging your wall will have full capacity. AISI S100-07 D3. Simpson makes a product for this application LSUBH Bridging Connectors

 

[jayrod12]

So then when they push back due to cost, you tell them that installed exterior sheathing would be significantly cheaper. Problem solved.

 

[RWW0002]

Thanks Sandman. I will definitely have to look into those. The information provided by Simpson looks to be very useful.

 

[sticksandtriangles]

Clark Dietrich also provides a clip similar to the one Sandman linked. FB drop in clip.

They state that it only acts to brace the stud when it less than I believe 8" inches in depth. I have always counted on this to brace my stud in my design and not required sheathing on the exterior face; no complaints yet from contractors on the price.

 

[EngineeringEric]

I do like that the cost it will take me to analyze, specify something different, bigger studs, have the contractor install it wrong, have the contractor fix it, beefier brick ties... all of this has to offset the cost of dens deck that will provide a better building in the end.

Also you can bring up the current energy code being based on assemblies that may require dens, you have Air barrier requirements for buildings, you have NFPA 270/258 (? the bad one, whatever that number is) that only has testing on assemblies...

 

[RWW0002]

Thanks for the input. I like having the exterior sheathing as well. If I can get the bridging & clips to work for my stud depths at least it gives me a fallback plan.