Exterior Wood Wall - can diagonal member be used in lieu of sheathing

[ajk1]

In a cottage, the architectural drawings show no wood sheathing on the exterior face and 1/2" gypsum wallboard on the interior face. The contractor has provided a diagonal wood member.

The architectural drawings call for:

Exterior cladding (contractor used vinyl cladding)
1.4" rigid insulation
Metal corner bracing
2x6 studs @ 16
R23 bib insulation
6 mil vapour barrier
1/2" gypsum wallboard

Since there is no wood sheathing, presumably the diagonal member must take all the wind load down to the foundations.
Is that normally done?
Is it ok?

What is meant by "metal corner bracing"?

 

[precast78]

There's got to be exterior sheathings. How do they mount the vinyl sidings?

 

[JAE]

The IBC and the IRC recognize gypsum board sheathing as an acceptable shear wall mechanism.
Don't know what code you are under.



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[EngineeringEric]

Let in bracing? or are you talking about temporary diagonals?

 

[CANPRO]

Ajk1, see link below for a general description on how these types of walls are braced. From what I have seen, the metal strap brace is common. Obviously you'll need to take a look at how they installed it to make sure it is adequate. Based on the picture you posted in your other thread about the masonry piers, it looks like at least 3 of the "metal corner bracing" would be interrupted by openings in the wall.

http://www.finehomebuilding.com/des...ns-for-shear-bracing-foam-sheathed-walls.aspx

 

[msquared48]

The diagonal bracing is temporary to hold the wall square during erection. The GSB wallboard is shear rated too as JAE said, as long as it is shear nailed.
Are there any holddowns?

Mike McCann, PE, SE (WA)

 

[manstrom]

Diagonal bracing is considered under IRC.

It's crap, though. You can't make the loads work in statics. Gyp sheathing would make more sense. Of course, there is some requirement (I believe) for some kind of exterior covering to keep stuff from flying through the wall during a high wind event.

 

[jayrod12]

And gypsum is limited as the the proportion of the total shear force resisted by the building. For a 1 storey building it can be up to 80% in the canadian design codes. However I've always been leery about using gypsum unless necessary.

 

[msquared48]

Page 267 of my 1958 Douglas Fir Use Book shows a relative rigidity of 1.6 for a horizontally sheathed (1X8) with 2X4 let in bracing, and 4.3 minimum for a 1X8 diagonally sheathed wall with no bracing.


It is not as good as sheetrock or GSB. The GSB is stiffer, so use that value for the shear. The let-in bracing is just extra.

.

Mike McCann, PE, SE (WA)

 

[ajk1]

I have not seen the cottage so I do not know what they did. But the drawings call for what I listed in my original post. I imagine that they fastened the vinyl siding to the wood studs.

Where a permanent let-in diagonal wood brace has been used, or a metal corner brace as called for on the drawings, does that make sheathing on the exterior face of the studs unnecessary?

Can the 1/2" gypsum wallboard on the interior side of the wall studs serve to take the place of the exterior sheathing, as far as the structural aspect is concerned to resist wind forces?

The Code is the Ontario Building Code, Part 9. It is very similar to the National Building Code of Canada.

 

[msquared48]

In answer to your third paragraph, yes, if it is nailed properly and blocked if required.

Mike McCann, PE, SE (WA)

 

[ajk1]

msquared48 - ok, thanks.

 

[ajk1]

Do you know where in the National Building Code of Canada that gypsum board is allowed for use as structural sheathing, and what the nailing and blocking requirments are when it is used structurally like that?

 

[msquared48]

I don't. But BAretired should...

Mike McCann, PE, SE (WA)

 

[jayrod12]

It is in the wood design manual Section 8 - Shearwalls and Diaphragms. Gypsum values are specifically discussed on page 443. The drywall must be type 'X' (I assume type 'C' would work as well). If it is for seismic resistance your Rd = 2. They must be used in conjunction with wood based lateral resisting (i.e. you cannot count on gypsum for 100% of your lateral capacity).

CSA O86 clause 9.5.4. and tables 9.5.1B and 9.5.4

NBCC 9.23.13.1.2.(a).(ii)

 

[ajk1]

Thanks Jayrod12, when I get into the office I will look at those references. I assume that you are referring to the 2010 edition of the Wood Design Manual and NBC. I do not have those editions here at home.

 

[jayrod12]

I think the 2005 version had the same provisions

 

[Canuck67]

This is one of the standard construction assemblies permitted under the Ontario Building Code, has been for several years. Some builders like, some don't. With this requirement is a rigid insulation board on the exterior of the studs, through which strapping is attached and then the siding.