Insulation board between studs and sheathing in shearwall 1

[MAeng]

Hi folks -

I've just encountered the really odd circumstance of a building in which the siding (T-111 in this case)is applied exterior to 1" rigid insulation board, which is nailed to the studs. Obviously not the ideal situation for any type of braced wall. Has anyone seen any literature about how/if sheathing can be nailed thru the insulation board and have any shear value? I've never seen this situation before. Hoping there might be a way to save the owner the cost of fully re-sheathing the house. I'm not optimistic.

So - to review: studs @ 16" O/C, then 1" rigid insulation, and finally T-111 at exterior.

Thanks in advance.

 

[jayrod12]

How did that get by everyone to begin with? I don't know of any specific guidance off hand. Any proposed fixes on my end may be harder/worse than removing and re-sheathing the exterior.

 

[MAeng]

We were wondering the same thing. Sigh.

Thanks.

 

[Deker]

Would it be cheaper to sheath the interior side of the wall with plywood?

 

[MAeng]

Hi Deker - Definitely considering that.

 

[jayrod12]

That was going to be my recommendation. Likely the most effective and easiest option. Doesn't make it any cheaper. And may mess up the rated assemblies for the architect if there are any.

 

[kipfoot]

Huber zip system makes an insulated sheathing that has some capacity, tabulated in ESR 482. If the load's not too high, maybe there's a way to justify it by analogy.

 

[XR250]

I agree with Kipfoot - although T1-11 is not OSB and was not tested so you would being a bit of a Cowboy. Like others have said, sheathing the interior may be the best option.
On a related note, i was at Lowes last night. 7/16" OSB is $45 per sheet! I remember back in 2007ish when it was $4.99. I paid $18 in november when my house was being framed - now that seems like a bargain!

 

[kissymoose]

Huber zip system makes an insulated sheathing that has some capacity, tabulated in ESR 482. If the load's not too high, maybe there's a way to justify it by analogy.

Not just trying to be a debbie downer, but this is probably a dead end. Huber's ZIP-R has the sheathing stuck to the foam, some shear is being transferred there. No idea how to quantify that, but they did enough testing to get an ESR report. Any semblance to the system that's not ZIP-R isn't qualified under the testing with no good way to get quantified strength.

 

[MAeng]

I agree Kissymoose. I'd need something I feel it quantified by empirical testing or at least some certified capacity. Thanks everyone!

 

[skeletron]

I'm seeing that ZIP sheathing all over the place with framers in Pacific Northwest (seismic) zones mainly because it simplifies the wall sheathing/cladding process and because it has a really decent energy rating. This stuff has to have a capacity that those engineers are using?!

 

[HouseBoy]

To answer the question - APA E30 and E300 indicate that (some) T1-11 can be rated sheathing.

The most recent IRC requires increased R values for walls and roofs. One way to achieve that (the latest dance craze around here) is to provide a continuous layer insulation at the OUTSIDE. (LEED folks also are really big on sealing up EVERY air leak)
Huber came up with the Zip-R-wall product (as was mentioned) that you can get in different thicknesses. I've seen others try to make their own by using rated sheathing over rigid foam boards.
This case is "cowboy" on both counts (separate insulation board and the sheathing)

Considering this idea (sheathing OVER insulation) is coming on..... what are local plan examiners requiring for calculations of this assembly?

 

[MAeng]

I'm just looking for some entity that has tested values for sheathing with insulation between the sheathing and the studs. My view on it is that such an arrangement would actually cause a nail to be subject to shear AND a moment. I do not believe I could reliably calculate a value for this. Zip is providing this as a board (Allow v in the neighborhood of 240#/ft. if I recall) but again it isn't a separate entity.

 

[HouseBoy]

APA put out this report from testing (attached)

 

[MAeng]

Thank you Houseboy. Much appreciated.

 

[Aesur]

I'm going to make an assumption that the house was designed using the IRC and braced walls, if so, have you considered taking the engineering approach and figuring out if you really need the whole house re-sheathed or just a few walls here and there, maybe it's as simple as taking a 10' section of each wall and apply sheathing and post installed holdowns if needed.

 

[MAeng]

Hi Aesur - That is an approach I'd advocate but as it turns out the window changes and the now planned siding replacement has made that idea moot. Thank you!