Vertical or Horizontal Sheathing? Which is right?
That is a question I get a couple of times a week. In some parts of the US or Canada wall sheathing is either installed vertically or horizontally and often it comes down to just a regional preference. In this short post I’d like to pass on some information that should shed some light on this topic.
First of all, install it the way that the engineer or designer requires it. You may be able to talk to them or the Authority Having Jurisdiction (AHJ) and change it to what works better for your crew. Now to get into the nuts and bolts, or should I say nails and sheathing (I’m sorry, bad humor), I’d like to point to two references (which will end up being quite a few more than two), the 2015 Special Design Provisions for Wind and Seismic 2015 (SDPWS) and APA Engineered Wood Construction Guide Excerpt: Wall Construction E30-Walls .
The SDPWS is a little dense so to simplify it, here is what we need to know. All panel edges must be blocked in a shear wall or “braced wall”. The “braced wall” is a label for prescriptive wall bracing in the International Residential Code. Regardless of whether wall sheathing is installed horizontally or vertically, the edges must all be supported (SDPWS 4.3.6.1). Panel edge nailing is the important point here.
According to the APA reference (E30-Walls) page 3 Table 22 footnote a, “Panel strength axis parallel or perpendicular to supports”. Now here is the salient reference to me, E30-Walls page 6 Table 23 footnote C “All panel edges backed with 2-inch nominal or wider framing. Install panels either horizontally or vertically.” (bold mine)
What is the point? For the shear wall or braced wall to meet the design loads it must have proper edge nailing as called out by the designer. The tables in the code or other reference call out spacing on the edge nailing. Running sheathing horizontally without blocking the panel edges limits the edge nailing along the long edge of the panel to a nail every 16” (typically).
What does the "strength axis” stamp mean then? Here is a very clear explanation from Norbord. Notice the explanation of the grade stamp on the APA rated sheathing, “11. The strength Axis indicates the direction of the board that has the most strength. When installing subfloor and roofing, the panels must be installed with the strength axis perpendicular to the supports. When installing walls, the strength axis can run either vertically or horizontally to supports.”
We can reason on this too. Most 4x8 OSB panels have nailing lines running both directions on the panel, and 4x9 and larger only have them running parallel with the long edge. Again check locally because certain conditions, e.g. high winds, can require sheathing be run horizontally to help stiffen the wall assembly. Stud spacing can also be reduced to meet those loads as well. On balloon framed walls our engineer will often call out stud spacing 12” o.c. or doubled studs 16” o.c. In those cases I ask for a design to include LVL or LSL studs instead.
What about staggering the seams? Thor Matteson in his book Wood-Framed Shear Wall Construction on page 110 section 3.7.7 says that “shear walls with staggered panel joints will deform about 25% less than walls with all the joints lined up.” Then he follows up by saying “Personally, I feel that the framer’s time is better spent in taking extra care while nailing than staggering rows of blocks”
Here is my take as a non engineer (so it is worth very little). As Thor states in his book, if your designer requires staggering, then “stagger away”. In most cases by fully sheathing the wall, we already have a wall that is far stronger than it needs to be. So be careful about using the argument that because it is stronger that is the way it should be done.
Is it as strong as it needs to be? If yes, then move on. A simple example would be that if a 4x10 header is properly sized for the opening we don’t size up to a 7” x 18” glulam.
Conclusion. Go buy Thor’s book, subscribe to The Journal of Light Construction and read the manufacturer’s information. It makes us better framers and teachers. We all win.
