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Are 3x Studs Req’d. @ Panel Edges of 24″ O.C. Exterior Sheathed walls?

Spencer Burnfield | Posted in Building Code Questions on

Hello,
The structural engineer I use just gave me a call. He was reading the NDS (National Design Standards) and found that 3x studs are required at 24″ O.C. framing that is sheathed w/ plywood/osb. I am assuming this is a requirement only at shear walls, but in the Northwest at least just about every exterior wall is used as a sheathed shear wall.

I was wondering if anyone else has run in to this or if engineers/plans examiners have just been ignoring it?

Another related note is that I was discussing 24″ o.c. walls with a builder the other day. He noted that he had just finished doing a house with 24″ o.c. walls and that due to the lack of extra studs for strength the O.S.B. had a tendency to pucker the wall (a curve from top to bottom). I asked him if he thought that it was a problem that you would only find with O.S.B. or would plywood do it too? He thought as I did that it would probably only be a problem with O.S.B….which is fine with me cuz I don’t really like it on my walls anyways.

I keep trying to get wood out of walls, but engineers and builders keep trying to add it back in. =)

Thoughts?

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Spencer,
    Engineers design walls based on a variety of factors, including wind loads and seismic loads. Here in Vermont, we don't use any 3-inch-thick studs when framing walls with 24"-on-center studs, but in areas with high winds or earthquakes, you generally have to do what the engineers tell you.

  2. Spencer Burnfield | | #2

    Right, I may check with another engineer I use to see what he thinks. I had never seen it here either. What he was referring to though was an NDS standard. I thought that should apply just about everywhere. I know that sometimes things get updated in standards like that and sometimes people don't realize that things changed. For example, code went back to 6" stem walls for two story applications. I think it took a year for me to realize this change and every builder I told had no idea it had changed. I am curious if this is true in this case.
    The same engineer also noted recently that Simpson Strong Tie has reduced a bunch of loads for their connectors as well. I am not sure if he gets bored and looks stuff up like this and the general population hasn't realized the issues yet, if he is just way off the mark, or these are issues that the general building world has seen and dealt with already.
    Thanks,
    Spencer

  3. TJ Elder | | #3

    Spencer,

    This engineer sounds like a novice. End studs at shear walls are not always 3x, they may be 2x when loads are light or sometimes 4x or 6x in multistory structures with larger loads. The calculation is straightforward and depends on the mass supported and the wall height and width. Making the wall stronger (increased shear capacity) usually means extra nails in the sheathing, and 3x lumber is required when nails are closer than 3" on center. See the APA charts here: http://www.apawood.org/pdfs/unmanaged/E30wallT25.pdf. Also to better understand seismic design see this: http://www.naffainc.com/x/cb2/Struct/Sheawall%20basics.pdf.

    Edit to say, if this is about studs behind panel joints (48" o.c., every other stud) and not just end studs, then it's understandable that you'd be annoyed at the extra lumber, inconsistent with the goals of OVE framing. There are some illustrations and photos in the second link above showing what happens when too many nails go into a 2x at a panel joint, and the stud splits.

  4. Spencer Burnfield | | #4

    He's been around for quite a while. He has worked from California all the way up the coast to Washington and is in his 60's. Great guy but sometimes he can be a bit conservative. I think what he is doing is reading the fine print on things that the majority of engineers in the area have either not noticed (if it was a new thing) or have chosen to ignore it in favor of "well we've been doing it this way for a while now and we like it". I can see the latter happening because just like politicians they don't really want to be the bearer of bad news to contractors since whoever the first one is to do so will bear the brunt of the frustration (more like won't get hired until more engineers jump on board as well). He happily engineered things without 3x studs until two days ago =). I think he is just trying to cover himself legally by towing the line. I just wanted to see if anyone else had run into this/if this was normal anywhere else.
    I did a little research and it looks like some of the guys from Cali on JLC were talking about this becoming common place down there.
    I definitely understand why they want 3x studs at the panel edges. I figured that out after the first time I nailed a Simpson strap in place at a corner =).
    Thanks,
    Spencer

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