Wall Bracing (and Other Bracing)

[MountainDon]

This information is from the following website:
http://mgacon0.tripod.com/plywood.htm
It's a California construction firm website. There are popups, so be aware.

I'm reproducing the important data below. The absolute values given on that website have been "eyeballed" by PEte who says they do look about right. This compares the traditional let in 1x4 wall bracing with plywood sheets.

The first image is the 1x4 let ins...  Their calculations indicate it would take a force of 245 lbs applied laterally to the top plate to deform the wall. Let it be noted that the illustration has an inaccuracy. The 1x4 should also be let into the bottom and top plates for maximum strength from this method. There are also metal straps available for this, and Simpson has some T profile metal straps.




The next illustrated method is to use 1/2" plywood panels at just the corners. In between non structural insulating sheathing is used by some builders. The corner sheets are placed vertically and nailed according to code, 6" spacing on edges and 12" spacing in the panel field. This method is over 5X as strong as the 1x4 let in bracing.




The third method illustrated is to use 7/16 or 1/2" 4x8 structural plywood or OSB sheets placed horizontally in an upper and a lower row. Again panels are nailed 6" on supported edges and 12" in the field. Note this example does not use any blocking at the horizontal seam between panels. A twenty foot long wall section like this will be  10X as strong as the wall with the 1x4 let ins, and almost double the strength of the wall with plywood panels at the corners only. Note that a problem with horizontal panels without blocking is that a force applied to the upper plate down the length of the wall can cause the upper panels to slide horizontally in relation to the lower panel.




The fourth illustrated method is similar to number three; the plywood or OSB sheets are installed vertically. This permits all the panel edges to be nailed on 6" centers with 12" in the panel field. Because all the edges are nailed, this gains some strength. This wall construction calculates out to being more than 13X as strong as the 1x4 let ins.



Note that if blocking is nailed in at the horizontal panel joint in illustration three, the horizontal panel placement will calculate out to be equal to the vertical panel placement.


With the above in mind some comparisons can be made of the relative strengths of a pier and beam foundation, fitted with diagonal bracing, and other foundations such as permanent wood foundations and block or concrete perimeter walls. Something to think about. An engineer would have to run numbers but I'm certain that similar strength ratios would be found.

[Alan Gage]

Thanks for posting that Don. I'd found that somewhere once after lots of looking and have never been able to find it again.

Alan

[MountainDon]

Wow, a hundred views since I posted this. There is some sarcasm there, BTW.

I just wanted to add, to impress that the absolute values stated in the examples have not been verified by tedious calculations, but the ratios or relative differences between the types of bracing is going to be close enough for government work.  

[Don_P]

Well, not really, I think I peeked 3 times  
That is a good graphic, I've built with let in braces and the simpson cut in T braces in the past  . Full sheathing is by far my preference. These numbers show it, also the pictures of flying debris damage being stopped by full sheathing.

[JRR]

Retrofitting "shear walls" into an existing building is covered in this month's (Nov, 2011) Fine Homebuilding.  Expected are the vertical sheets of 1/2" plywood, edge-nailed every 3" ... but nails should not be driven within 3/8" of plywood edge.  To this end, 4x4's are to be substituted for end-studs and at sheathing joints.  Could be difficult to do this stud replacement in a "retro".  And no mention of adding construction glue.  

However, very much worth "a read".  Many good ideas to include in a new construction.

[MountainDon]

And no mention of adding construction glue.  

That's right. I believe glue is used for things like floor to combat squeaks more than anything.  The presence of glue can place more stress on the nail when a lateral force is applied because the glue acts as a spacer, keeping the plywood from having intimate contact with the framing. The failure with glued panels can be more dramatic than the slight creep that may happen with properly nailed sheathing.

I think. If I'm wrong we'll correct that.

[Squirl]

I don't know if you are referring to the original article for the Fine home article, but the original article was written in California.  IIRC, construction glue was not to be used in high seismic zones because it takes away the flexibility of the wall to move in a quake, making it too rigid. 

I had asked my inspector about it, he said why bother.  I added I wanted something that would last longer to give a better air seal of edges.  I asked about the rigidity concerns.  He laughed and asked if I thought I was in California and not NY.  He told me to go back and check the seismic zones again.

[davidj]

Retrofitting "shear walls" into an existing building is covered in this month's (Nov, 2011) Fine Homebuilding.  Expected are the vertical sheets of 1/2" plywood, edge-nailed every 3" ... but nails should not be driven within 3/8" of plywood edge.  To this end, 4x4's are to be substituted for end-studs and at sheathing joints.  Could be difficult to do this stud replacement in a "retro".  And no mention of adding construction glue.  

However, very much worth "a read".  Many good ideas to include in a new construction.

Having had my Bay Area crawl space retrofitted 10 years ago, it's reassuring that the article describes pretty much exactly what they did to my place right down to the same exact hardware.

[JRR]

Wonder how the plywood would perform? ... without the glue.  

Just saying.

[PEG688]

FWIW , I'm pretty sure the manf. of OSB and Plywood  don't want their sheathing glued  of 7/16" / 1/2" material , they want it to be able to "move" some , if you glue it,  its prone to bulging between studs. 

I'm  not sure where I read that , but maybe a Goggle search could turn some thing up on that.