Plywood Sheathing Horizontal Splice

[jdgengineer]

I have a project where we are running the exterior wall plywood vertically. The building is two story with a relatively tall first plate height. The contractor is trying to run a continuous panel from mudsill (below 1st floor joists) to 1st floor top plates but will be about 2" short. He'd like to block right under the top plates and splice the plywood on the block. All edges will be fully blocked with edge nailing. The upper plywood panel would run all the way up to the 2nd floor top plates.

With this approach all of the horizontal splices of the plywood will align. I know it's general practice to want an offset in the splice locations, but I can't find any requirement in the NDS SPDWS or IBC. This is a fully blocked and nailed shear wall.

Is this a requirement or just general common practice? Does anyone know of a code reference that requires the offset in splice locations?

 

[CANPRO]

I don't see a lot of walls, if any, with plywood running vertically so I can't say what would be common practice for splice locations. It would seem like good practice to stagger the joint though - couldn't the contractor cut 2' of every other sheet and install it on the bottom? Not that much more work really.

Structural considerations aside, this sounds bad for insulation purposes. You're going to have a tiny little gap between the top plate and the blocking...or blocking tight to the underside of the top plate. Either way, not ideal.

 

[TehMightyEngineer]

I know of no requirement that the splice location be staggered. If I had to surmise, that's what the blocking is for.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL, HI)

 

[jdgengineer]

He could cut the panels and is reluctantly willing to, but it is more work and this lays out relatively well.

In looking through Breyers book, the SDPWS, and the code I didn't see even a conversation about it. The SPDWS commentary mentioned doing tests with different size infill panels of plywood when the sheet was continuous but I believe their testing showed that it didn't really matter.

With that said, most other drawings I've seen show the splice offset, but I don't really see a lot of great documentation for it. For a diaphragm, I don't think the SDPWS would give a higher capacity for a blocked diaphragm with either configuration of the splice (it would for the panel running horizontally instead of vertically)

 

[KootK]

If this is street legal, then what you're proposing must surely be street legal-er.

 

[molibden]

It is funny how different practice is in Europe. First of all we use OSB and place it on the inside of the wall. It acts also as a vapour barrier. All other layers towards outside are vapour permeable. All OSB is placed vertically - if possible full height in one piece (up to 3 meters). In such way all edges are nailed/stapled to timber frame. There is no OSB connecting walls between stories.
I believe there is reduced shear resistance of the wall with horizontal sheathing. Is that true or just unblocked ones?

 

[jayrod12]

Is that true or just unblocked ones?

I would argue that it's more due to the fact that the guys don't want to block the panel edges. So it's less stiff in that sense.

It is significantly easier to sheet long walls horizontally, or at least I think so when I'm framing (which unfortunately I don't get to do much anymore).

Usually for me, I start with an unblocked assumption anyways and hope to get it to calc out. There's people in our office that as soon as they consider a wood wall a shear wall it's automatically blocked. What a waste of blocking and effort.

 

[molibden]

Well in Eurocodes we don't even have unblocked shear walls so it makes more sense to have sheathing vertical and no blocking required.

 

[KootK]

Vertical wall sheathing has always appealed to me on a mechanical level. It feels good to have a direct connection between the thing that you don't want moving laterally (top plate) and the thing that you are ultimately relying on to accomplish that (bottom plate). The upper level sheathing will still get boundary nailed to the lower level top plate, right? I would assume so and, if that's the case I would have every expectation that the wall would actually perform better than a horizontally sheathed system with staggered joints.

There is no OSB connecting walls between stories.

Interesting. Do you know the rationale for that? I would actually prefer that myself but my rationale is probably a bit paranoid. I worry that the bits of sheathing that cantilever up or down from the walls generate a sort of backstay effect that might generate unexpectedly high shears in the fasteners at the ends of those cantilevers. Of, course, on the other hand, sheathing across the plenum is great for holding things together under high wind etc.

 

[jdgengineer]

Thanks guys. Yes KootK the upper sheathing will be nailed to the lower top plate.

Quote (molibden)
There is no OSB connecting walls between stories.

Interesting. Do you know the rationale for that? I would actually prefer that myself but my rationale is probably a bit paranoid. I worry that the bits of sheathing that cantilever up or down from the walls generate a sort of backstay effect that might generate unexpectedly high shears in the fasteners at the ends of those cantilevers. Of, course, on the other hand, sheathing across the plenum is great for holding things together under high wind etc.

I'm assuming that's because molibden stated the OSB is usually applied to the inside of the wall so it would be difficult to have the OSB run through the floor in this configuration.

 

[Ron247]

Is there a possibility of the uplift at the corners separating the horizontal plates since the sheathing does not secure one horizontal plate to the other? At that level, there may only be nail withdrawal. I am trying to picture your situation but I think you have 96" sheathing on a 97 1/8" wall wall. When you let it set slightly below the sill plate the difference gets to about 2". You would have the identical problem with 2 runs at 48" though.

Also, if you cannot get the lower sheet to the 1st floor top plate, how does the next level get to the 2nd floor top plate? Is the wall shorter on the 2nd floor?

 

[jdgengineer]

The top plates are 11' tall and the contractor is using 12' sheets of plywood. The first floor joists are 11 7/8 which I think means the plywood is roughly 3" shy of the top plate if the plywood is also nailed to the mudsill. He is going to use 4x blocking and both the lower sheet and upper sheet will be nailed to it. The upper sheet will be nailed to both top plates, the rim joists, and the sole plate of the upper wall. The 2nd floor plate height is 10' so the panel can reach all the way to the top plates.

 

[molibden]

I'm assuming that's because molibden stated the OSB is usually applied to the inside of the wall so it would be difficult to have the OSB run through the floor in this configuration.

Yes, that is the case. For shear and uplift forces we use screws, brackets, hold-downs.. so basically extra sheathing at floor level seems redundant

I would actually prefer that myself but my rationale is probably a bit paranoid. I worry that the bits of sheathing that cantilever up or down from the walls generate a sort of backstay effect that might generate unexpectedly high shears in the fasteners at the ends of those cantilevers.

Probably similar case when I want OSB sheathing to be 10mm shorter at the top and bottom. In case of horizontal load it can then freely rotate and not lean onto floor/ceiling, which would cause extra shears in the fasteners.