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Losing the "exterior" sheathing argument

Joe Engel

Member
Joined
Jun 16, 2011
Messages
59
Location
MIssissippi, NW
Anybody seen PE's using drywall inside as structural sheathing?

Taking issue with structural sheathing exception for connecting studs to plates. New bank by local (NW Ms, seismic zone D) design firm and structural PE calls for truss roof with 12 foot, 2x6 walls and 1" non-structural foam to support 3" of closed cell foam. PE calls for 5/8 X drywall as structural sheathing on inside, all seams blocked, screws 8" and 12". I did get plywood corners by refusing to enter for inspection. Four Simpson strong walls on plan parallel to long dimension. I've asked for metal connections at stud to both top & bottom plates. PE says their not needed and it fill be fine once the drywall is installed (after black-in inspection). Load calc's over my head, asked for specific letter for file from PE siting code and materials used in design.

Is this a new trend?

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I see gypsum shear all the time. There are methods prescribed in the IRC chapter 6 for its use. I have not seen it as the sole method of lateral bracing but without looking it up I think it is in there. For a commercial building, I think chapter 23 covers the same. In any case, if the PE designs it based on those code sections and there are no blatant errors in his design......
 
Same value interior or exterior.

The effective length of the wall and the shear running through other walls , and electrical boxes are the issue.
 
I did get plywood corners by refusing to enter for inspection.
Assuming that's 4'x12' of brace. The shear value of that is quite large in comparison to drywall. What nail pattern did you specify?

Four Simpson strong walls on plan parallel to long dimension.
Depending on the size, they may be all that's needed and the drywall is icing on the cake.

I've asked for metal connections at stud to both top & bottom plates.
That and the plywood corners that you required have made you responsible for the design of the building. Not that I'm against that per se, but now that the bracing has been beefed up, you should analyze the anchor bolts.
 
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I'm curious how you can rationalize your own personal building requirements before an inspection?

With all due respect, if I'm meeting the design and code, I might say pound sand. If you are using the bracing before entering as a safety blackmail I would start to think we're starting to play games or something.

Brent.
 
Not saying PE can't make a mistake but like ICE said, you might own the design if you modify the design, and do you have the authority to modify the design? My position is to assume the PE has a better understanding of the particular design conditions on the project he has submitted the design for. When I encounter a peculiar design I make sure they have followed it exactly and unless something seems to be missed or is contrary to the code I simply follow the design. In those cases where I may have questions I address them as just that-questions, but I don't add to or modify the design. That would be designing without the license or expertise to do so.
 
Sifu said:
That would be designing without the license or expertise to do so.
As an experienced inspector, he may have the expertise....and "We don't need no stinking license"
 
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MASSDRIVER said:
I'm curious how you can rationalize your own personal building requirements before an inspection?
Theoretically the structure should stand without the bracing in place. But there have been a few that I wouldn't recommend removing the plumb and line braces before starting the shear. A big, naked box could qualify for that.
 
ICE said:
Theoretically the structure should stand without the bracing in place. But there have been a few that I wouldn't recommend removing the plumb and line braces before starting the shear. A big, naked box could qualify for that.
I would agree, but that's a self-licking ice cream cone. I won't pull the plumb braces until sheared or permanent bracing is installed, and I won't yank the line braces until trusses and the diaphragm are locked up.

Brent.
 
ICE said:
As an experienced inspector, he may have the expertise....and "We don't need no stinking license"
As much as I would like to think my decades in the construction business have given me the equivalent expertise as the structural design firm and the PE, I am not sure the courts or professional engineering boards would agree. After re-reading the OP I am unsure of the main concern. Is it the use of gypsum for shear or the fact that there may not be adequate shear until the gypsum is applied? Without full knowledge of the conditions, both concerns may be valid and asking for a clarification on those points are valid. Maybe I read more into it than was intended. I do tend to cringe a little when an inspector seems to be trying to over ride a PE's design, though honest skepticism is always healthy.
 
Sifu said:
I do tend to cringe a little when an inspector seems to be trying to over ride a PE's design, though honest skepticism is always healthy.
I agree. Build per approved plans and calcs.Trust but verify.....
 
There have been plenty of occasions that a building was built per the approved plans and it had a glaring flaw. When that happens I usually don't provide an alternative design. I inform them that the design as built didn't work and they need to provide a solution that will work. Sometimes it requires an engineer's approval but more often it's a less important mistake that I have seen many times.

Tossing in shear wall segments on a new building is not an option.....it's fair game on a remodel.
 
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Official credentials are key.

That does not guarantee the design is error free by any means, and even though I may know the solution, and at times even provide the solution, It would be foolish for an inspectigator to approve it without someone with the proper education and expertise to green light the thing. Not my place.

Brent.
 
MASSDRIVER said:
Official credentials are key. That does not guarantee the design is error free by any means, and even though I may know the solution, and at times even provide the solution, It would be foolish for an inspectigator to approve it without someone with the proper education and expertise to green light the thing. Not my place.

Brent.
It's a matter of degrees.

The degree one holds. The degree of importance of the perceived problem. I simply can't send people to an engineer with every concern. After getting the same fix for a situation a dozen times, I think that I am on safe ground to apply that fix without asking the next engineer. Lots of jobs don't have an engineer involved on their side.

Why should they pay an extra $500.00 for that MST-37?

If the frieze blocks are nailed to the V-rustic, I know what to do.

Stuff like that.

That being said, Brent is more right than wrong and I wouldn't recommend doing what I do where you do what you do.
 
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mark handler said:
Depends on what that strap is being used for and the loading; Blocking may not work
I usually add A-35s to the blocking and if the load is large it's a 60".

Now I'm just being difficult. Truthfully, I don't like straps on blocks. Plates yes, blocks only if there is no other way.

Anyway, the guy that started this thread wanted to hear about drywall as shear. I thought that went out with let-in braces but apparently not. So let's talk about value engineering.
 
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ICE said:
I usually add A-35s to the blocking and if the load is large it's a 60".Now I'm just being difficult. Truthfully, I don't like straps on blocks. Plates yes, blocks only if there is no other way.
A35's don't work for a drag or uplift or post holddowns
 
mark handler said:
A35's don't work for a drag or uplift or post holddowns
Well if you can trust an engineer, they tend to keep a block in one place. How about an LPT4 then.
 
Thanks Brent for the Contractors perspective, I've been on that side of the fence, too. I really appreciate all the input. It's the location of the "Sheathing" that raises hair on my neck. With foam on the outside and drywall an the inside, I have to trust that drywall was installed as prescribed in the plan. It most likely will be fine and the PE is the one that's liable, I just hate to sign off on something I can't verify.

I'm not a PE just 30 years OJT in Light Frame construction, why I'm recommending and not requiring. I try to assume the position of applying the code instead of enforcement. The OSB corners were suggested to me by the super & framer long before the trusses were even delivered; I just encouraged their use by letter to GC who was also in favor. The four Simpson SW24x12x6's may do the job well, I'm just "old school" and don't trust drywall hangers for critical seismic connections. Again, I'm concerned for potential of a trend in eliminating the exterior structural sheathing.

Color me Gray...
 
\ said:
Thanks Brent for the Contractors perspective, I've been on that side of the fence, too. I really appreciate all the input. It's the location of the "Sheathing" that raises hair on my neck. With foam on the outside and drywall an the inside, I have to trust that drywall was installed as prescribed in the plan. It most likely will be fine and the PE is the one that's liable, I just hate to sign off on something I can't verify.
Joe:

You are correct, walls have to breathe, permeable barriers don't work, if you put sheetrock on the inside foam on the outside will create the dreaded dual barrier, otherwise known as the mold sandwich. I never install plywood on the exterior and never install OSB period, if the engineer calls for it I get permission to install plywood on the interior behind the sheetrock, I am now moving to full red iron frames on my better homes. Another thing I would do is go back to installing diagonal 1x8 boards on the exterior, that's what I learned to do before plywood was available and it worked fine, the mills don't mill it anymore but my lumber yard says they will run 2x8s through their resaw bandsaw for me.

Interestingly I built a lot of apartment projects in the 60s and into the early 70s, many three stories + penthouse over a class A garage with the only bracing the sheetrock, in our earthquake zone there have been no problems to my knowledge., but I sure see pictures of failures after earthquakes, I guess I've just been lucky.
 
Personally I will not use drywall to resist lateral loads but this does not give the inspector the right to impose his personal beliefs. Rather than rely on the design engineer the building department should have the design reviewed by a licensed engineer as part of the plan review process. I would not be surprised if such a review would result in changes.

Any building department that does not have the ability to have a professional engineer plan check the structural design has problems. You have the authority to perform a thorough plan check so exercise that authority and have an engineer review the structural design. Enforce the building code, but the inspector should not impose his personal beliefs.

Building inspectors typically have deep knowledge regarding some portions of the code but this does not mean that they have total knowledge about all aspects of the building code.

Inspectors do pick up a lot of knowledge but this does not give them “…the equivalent expertise as the structural design firm and the PE…”. The reality is that the training and knowledge that a professional engineer has provides him with a different insight than can be obtained by performing inspections. Any inspector that believes otherwise is deluding himself.

At least in California it is clear that if a building official or inspector were to practice engineering they need to be licensed.
 
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