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On new construction, what is the proper way to install the exterior OSB wall sheathing?

Should I go for a perfectly level sheet install, and then level each corresponding sheet or is it better to just follow the edge of the sill plate and end up with potentially non-level panels due to the foundation not being floated perfectly?

I have also considered snapping a chalk line after measuring 47 and 3/4" from the sill plate on each end of the house, but that chalk line would be extremely long and would vary too much in that span.

I am trying to maintain:

  1. An even 1/8" gap between each sheet
  2. The same height of sheet as the next one to prevent unequal gaps on the 2nd row of sheeting, and
  3. Keep the sheathing flush with the bottom of the sill plate so it ties into the sill plate nicely with the edge nailing pattern. This has amounted to nothing but frustration and curse words.
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  • My answer assumes walls that have not yet been erected. After re-reading, I suspect this may not be your situation. Please edit to clarify.
    – isherwood
    Jul 18, 2017 at 14:26

3 Answers 3

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The code allows 3 basic configuration: 1) Configuration 1: long edge of panels installed horizontally across supports and each succeeding course staggered 1/2 panel LENGTH, 2) Category 2: long edge of panels installed horizontally and each succeeding course staggered 1/2 width of SHORT edge, and 3) Category 6 (I know, stupid numbering system, but Categories 3, 4 and 5 are just for loading from opposite direction.) Long edge of panels installed horizontally across supports and each succeeding course NOT staggered.

Most installations are Category 1, but the critical criteria in all categories is that the panels MUST fully meet (lap) the sill plate, both top plates and 1/2 of stud at ends. (Please stagger nailing into studs where the panels end, to avoid splitting of stud.)

This doesn't tell you HOW to do it, but I hope it tells you WHAT you need to do...and I think your question was asking HOW...

By the way, if you are using staples, the crown must be PARALLEL to the long dimension of the supports.

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  • Sheathing is installed vertically in 99% of homes here, which doesn't fall withing your 3 categories. I wonder if those are for hurricane zones.
    – isherwood
    Jul 18, 2017 at 14:36
  • @isherwood No, it's not just for wind or seismic, it's for any framing that you need to calculate the load (resistance). Actually, panels set vertically with each succeeding course aligned is Category 5. (Similar to Category 6, but with loading from opposite direction, well from direction 90 degrees to norm...
    – Lee Sam
    Jul 19, 2017 at 0:12
  • The category seems to be redundant besides the staggered joint on the second row. Sheathing is installed horizontal here. I don't see the gain in vertical installation unless you can achieve one sheet per 4' of wall. Where as 9' or 10' sheets here would be too short even if I paid extra for the longer sheets. Working alone, those are not very friendly either!
    – CCCBuilder
    Jul 19, 2017 at 12:48
  • @Nic It has to do with which way the long edge of the panels span over the supports. I don't think it's a matter of strength, it's a matter of convenience (preference). I doubt it contractors are calculating the difference loading.
    – Lee Sam
    Jul 19, 2017 at 14:53
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The key is squaring your wall very carefully before you begin. If you do that, you can align your sheathing to the wall however is most convenient. Here I assume that you've snapped lines on the deck to set the wall plate on after it's sheathed and erected.

  1. Straighten the wall. Position the wall precisely on the position line, both in-out and endwise.
  2. Secure the bottom plate. Use 8d or similar nails and, from the inside of the stud bays*, tack the bottom plate to the deck at intervals adequate to straighten and retain the plate position. Doing so inside the stud bays allows you to easily remove those nails after the wall is erected. Otherwise they're inaccessible and can hold the wall off the deck.
  3. Square the wall by taking diagonal measurements from bottom left to top right and vice-versa. Shift the top plate until the dimensions match. Tack the top plat in position from the top of the top plates so the nail can be removed before erecting the wall.
  4. Set the first sheet. Determine the top location for your sheathing. Often this is simply the center of the double top plate for vertical installation. Set your first sheet (at any sensible location) at that top position and aligned with the center of a stud layout.
  5. Set all remaining sheets at the top and gapped 1/8" at the sides.
  6. Erect the wall. A poorly-constructed foundation can leave gaps under the wall where low spots occur. Make repairs to level the floor, or shim these as needed under each stud.

This results in a wall that's not dependent on your floor's flatness or sheathing position accuracy for squareness and straightness. Obviously squareness directly affects plumb in adjacent walls, and straightness issues translate to fascias, second floors, etc.

If your walls are already erected, I'd install sheathing vertically and set to the top plates as above, or use spacers and simply stand them on your foundation with a gap. The walls are what they are and how you sheath them isn't critical to much else as long as the sheathing is fastened and blocked properly.

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  • What is the true gain of vertical over horizontal? The walls are erected and I have been going along and been able to go by the bottom of the sill plate. It's looking a lot better now and very clean. I have noticed some floor joists are longer making the rim board and floor sheathing 'bow' out at a few spots due to me measuring the joists exact per edge of the concrete which is not perfectly straight. This means my OSB has to curve from sill plate over the bulge in rim and floor back to the outside of the stud. It's not noticeable in the OSB but my siding is likely going to need something
    – CCCBuilder
    Jul 19, 2017 at 12:51
  • Vertical doesn't require blocking since there are no joints spanning voids in the framing. You should fix your bow issues behind the sheathing, ideally.
    – isherwood
    Jul 19, 2017 at 13:38
  • Oddly enough the blocking is not required here. Are you in a hurricane zone? Is there a lot of strength lost when you run horizontal and don't have blocking on the seams? I had a heck of a time removing one panel earlier with only half the nails in it at the time. They were 2-3/8" ring shank. What nails are you using when running vertical?
    – CCCBuilder
    Jul 19, 2017 at 15:04
  • Narrow-crown staples. The problems with not blocking is misaligned edges due to warping, spongy nailing near the edges, and reduced diagonal brace strength.
    – isherwood
    Jul 19, 2017 at 15:21
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Plywood has a strength axis which is horizontal. The application is stronger also because the span is 16 or 24" compared to the wall height ( assuming no blocking is used ) Inspector Jeff ICC/FL/SC licensed combination building inspector and building designer

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