Nail base screws 1

[DoubleStud]

So I have a project where we frame the wall with conventional 2x6 framing and plywood/osb sheathing. The architect wants to add 3" nail base. Basically 3/4" ply that is glued to eps foam. The spec does not mention anything on how to attach it to the wall framing. The spec just says fasteners per engineer. How do I figure out how to attach it? I am not sure of the capacity of any screws when there is roughly 3" of foam in between. Here is a manual from one manufacturer.

https://www.thermapan.com/wp-content/uploads/2019/09/ThermapanInstallationManual-Nailbase.pdf

 

[SWComposites]

Google found this:

https://www.trufastwalls.com/sip-screw

 

[phamENG]

Say NO! At least, say no if you have any sort of demand in your shear walls or if you're using your sheathing for uplift.

ZipR sheathing from Huber has a third party test report that gives values in a table that matches the SDPWS shear wall capacity tables and one that gives IRC braced wall equivalencies. At three inches, it's going to hurt. I've looked at 1 and 1.5" insulated ZipR shear walls - the strength was okay but the flexibility was atrocious. It's because your failure mode is almost entirely nail bending. Screws wouldn't be a great fit for its. And SIPs aren't a good stand in - they typically have plywood on both sides of the foam, so the connection behaves very differently.

 

[DoubleStud]

it wont be used for shear wall. We have 2x6 framed wall+plywood behind it as well.

 

[phamENG]

Oh. Well that's different. All you really need is a screw capable of resisting wind suction loads or seismic loads (though I can't imagine that would be...anything).

 

[DoubleStud]

Pham, the problem is that any capacities listed for any screws do not consider having foam in between it. So I am not sure what capacity to follow.

 

[KootK]

I discussed this recently with a friend who was facing the same problem:

a) He never did find anything definitive in the literature etc.

b) The issue was really the gravity load.

c) He decided to use some diagonal screws to to set up a strut and tie mechanism with the foam as the struts. I don't remember if this was for all of the fasteners or just intermittent ones.

d) I really have no idea how one manages to hit the studs accurately when coming through the insulation.

 

[gte447f]

Can't these panels be self-supporting for gravity load (like brick veneer), and then you just need nails or screws for wind suction, like phamENG said?

 

[jayrod12]

Timbr-Lok (I believe it was them) had some research into the truss analogy KootK alludes to. In their opinion, it doesn't take much vertical movement for the screw to see tension instead of shear. I'll see if I can dig it up.

Edit: It was Headlok. Search for ESR-1078. Download link

 

[phamENG]

This might be of some use: Link

 

[DoubleStud]

pham, thanks for that link. I am not sure I understand the last table (second from last). What are those numbers?

 

[jayrod12]

I'm betting that is the screw spacing for each finish type and strapping spacing. It appears to be based on the maximum 10 lbs per fastener limitation.

 

[phamENG]

Looks like spacing of fasteners in inches. For columns of fasteners at 16"o/c and spaced 18 (inches), you'd end up with 2sf. For 5psf cladding, that's 10lbs on the fastener - the value identified by the description above as the limit for gravity load on any given fastener for 4" of foam.

 

[DoubleStud]

You guys rock, I can sleep well tonight.