Spray foam insulation shear resistance 1

[L_Bey]

I have a project where they were supposed to install wood sheathing on a shear wall, and neglected to do so. The contractor is now trying to argue that the densglass sheathing and spray foam should provide some shear resistance, so they don't have to strip off the existing gyp and provide the wood panels. This likely isn't going to work anyway, but I haven't been able to find anything on their claim of the spray foam insulation contributing to the shear resistance of the wall. I did find a couple of foam manufacturers who claim the spray foam insulated walls "have a racking strength up to 300% greater" (

https://www.sprayfoam.com/content/spf-strengthens-buildings/35),

but nothing that's actually providing any kind of design information. Is there any ICC report or anything else that would actually allow any additional rigidity provided by spray foam to be taken into account? It's unlikely to matter on this project specifically, but I've heard the claim before and my response has always been that unless there's some kind of a code report providing design guidance it's pretty irrelevant from a design perspective. Has anyone else run across this?

 

[phamENG]

No, spray foam doesn't provide shear resistance. Densglass does, and you can find gypsum based sheathing values in the NDS, but they're weaker and more flexible than wood.

If the contractor screwed up, make them prove it. If they can't supply you with the industry recognized design standards based on sound, respected, and repeated research, hand him a sledge hammer.

 

[L_Bey]

Yeah, nothing is changing for this one - we can't even use the densglass, because the original building design was based on R=6.5 and incorporating densglass drops it to R=2.

I was mostly curious because this isn't the first time I've had a contractor try to claim that spray foam would make everything better. And sure, it's possible that it makes a building stiffer, but unless there's something that's actually documented it doesn't matter for design. 2 papers from the 90s isn't going to cut it. But if there actually are code reports that can be referenced I'd be interested to know.

 

[phamENG]

I could maybe see some high end spray foam stiffening a building exposed to wind loading, but not under cyclic seismic loading. If that's the stiffest thing you've got, it would crumble quickly.

 

[SteelPE]

I just love how it's your problem because they didn't do what you told them to do. I don't know who you are working for (owner, architect, GC), but I would just tell them kindly provide what we show on the drawings.

I am actually leaning away from doing residential and lt commercial building unless I know the players involved. I feel these guys are just using me to get their permit and then go do whatever they want... then it's a fight for me to get them to use the drawings. It's just not worth it.

I recently visited a 2 story wood framed office building I designed (3,000 square feet per floor... 6,000 square feet total). I found 16 errors with the framing from my walk through and I suck at finding these things. It was so bad I resorted to marking up the drawings with the errors. Luckily nobody what there and I could go about my business taking notes without someone following me around. On this project the owner is acting as the GC and constantly sides with the subs. I wrote my report and then forwarded it along with the framing markup to the architect to pass along to the owner.