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drywall as structural diaphragm

drywall as structural diaphragm

drywall as structural diaphragm

(OP)
Is there any reference or publication that would permit the use of drywall on the inside face of exterior walls to be used to resist lateral wind forces (parallel to the length of the wall) where wood sheathing is not used on the exterior face of the wall?

RE: drywall as structural diaphragm

The IBC has tables for gypsum board sheathing on wood studs for shear walls (also on steel studs).

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RE: drywall as structural diaphragm

(OP)
JAE - thanks very much. Do I have to buy the whole IBC code to get those tables?

RE: drywall as structural diaphragm

You can look at IBC online for free here: Link

Public codes is a free service from ICC I think, for online viewing only - printing and free downloading is not permitted.

Go to section 25 re gypsum, which will refer you to sections 2306.3 for wood-framed gypsum-sheathed shear walls or section 2211.6 for steel-framed gypsum-sheathed shear walls.

RE: drywall as structural diaphragm

(OP)
To Ingenuity - thanks very much. I did not know about that. It should be very useful indeed. Much appreciated.

RE: drywall as structural diaphragm

Don't know where you are, but I would not recommend gypsum wallboard in a high seismic area, even though it is allowed. If seismic forces control, you have to reduce the table allowable by 50%, and will still have to retail and patch the wall after an event as small as a 6.0.

Mike McCann, PE, SE (WA)


RE: drywall as structural diaphragm

(OP)
Table 2306.3(3)is set up in terms of staple fasteners. Is there any similar Table for nail fasteners?

RE: drywall as structural diaphragm

ajk1, check out IBC 2009, table 2306.7 here: Link

RE: drywall as structural diaphragm

The Gypsum Association has a variety of publications on structural and non-structural use of drywall, including some cautions on using it in certain structural applications. Many are free downloads.

RE: drywall as structural diaphragm

Also, the Forest Products Laboratory has some structural application papers for drywall.

RE: drywall as structural diaphragm

(OP)
To msquared48 - this is a cottage that is not located in a high seismic area, but thanks for the caution.

To Ingenuity - thanks very much. On further thought, the drywall would normally be screwed rather than nailed, but this table seems to cover screws as well.

To wannabeSE - ok thanks. I suppose I would have to buy this publication if I wanted to see the relevant tables, which may be worth doing. Thanks. Perhaps I should check with the Canadian Wood Council first.

RE: drywall as structural diaphragm

(OP)
The cottage which was built last year has vinyl siding on the outside face of the exterior wood stud walls, but no sheathing on that side. It has drywall on the inside face. The wall reportedly does have a diagonal wood member, but I doubt that is very effective because there would have been no "engineered design" of the nailed connection of the ends of the diagonal, and also there are openings in the wall so the diagonal extends only over part of the all. No construction photos been found to-date of this.

My first thought was perhaps that I can check if the drywall sheathing on the inside face can take the in-plane wind loads. I thought that I had found a solution when you people drew my attention to the load capacity Tables. However, I wonder if there is still an issue, namely that the drywall on the inside face of the wood studs would not overlap the wood perimeter rim boards and therefore has no way of transferring the in-plane wind forces down to the foundations. What do you think?

RE: drywall as structural diaphragm

If there is sufficient nailing to the top plate, sill plate, and end studs, along with sufficient anchor bolts, this should not be a problem.

Mike McCann, PE, SE (WA)


RE: drywall as structural diaphragm

(OP)
msquared48 - ok, good thought. Thanks.

RE: drywall as structural diaphragm

Does anyone get called by the drywall trade before the mud is installed? We have tried using drywall before for the diaphragm, but that trade never looks at our drawings so by the time we get to site everything is mudded.

RE: drywall as structural diaphragm

I've never received that call. I'm a bit leary of using drywall as a diaphragm in an existing, un-engineered application. Generic drywall fastening doesn't always suit diaphragm action.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: drywall as structural diaphragm

Generic drywall fastening meets the biggest fastener spacing the the wood design manual (in general). In fact, most drywallers I've seen use more than the 6" edge and 12" field rule. But I never consider the blocked condition (because rarely are wood walls blocked in residential).

I would likely be willing to accept the drywall in this application, it can't be requiring some crazy capacity or anything if it's wind-governed.

RE: drywall as structural diaphragm

@Jayrod, you've convinced me.

@ajk1: the CWC handbook tabulates the capacities that you're looking for in the Shearwall Selection Tables.. I'd reference a table number but they don's seem to have any. With 16" o/c studs, you'll get a minimum of 0.84 kN/m.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: drywall as structural diaphragm

We've used a drywall ceiling diaphragms before and didn't have any contractors cursing our name any more than usual. ;)

Maine Professional and Structural Engineer. www.fepc.us
(Just passed the 16-hour SE exam, woohoo!)

RE: drywall as structural diaphragm

ajk1,
The American Wood Council has a read-only pdf of the SDPWP that can be downloaded for free: http://www.awc.org/pdf/AWC_SDPWS-2015_web-viewonly... . If this link doesn't work, look below the "buy" icons for the link to the free pdf.

RE: drywall as structural diaphragm

jayrod:

All Plywood shear walls better be blocked. GWB and GSB, correct for the most part.

Mike McCann, PE, SE (WA)


RE: drywall as structural diaphragm

Mike,

The CWC publishes shearwall values for un-blocked wood diaphragms. I generally try to stay within the ranges of the unblocked capacities because I've had nothing but fights from contractors when specified.

They'd rather put twice as many nails into an unblocked shearwall then have to cut and install blocking at 4' or even 8' centres. It is anywhere from a 20-40% reduction in capacities depending on the specified nailing pattern.

RE: drywall as structural diaphragm

I would never do that here...

Mike McCann, PE, SE (WA)


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