Gypsum Shear Walls

[BSVBD]

I believe, in older IBC guidelines, it was necessary to use (2) layers of gypsum wallboard for shear walls - (1) layer e3ach side of wood stud wall.

In the 2008 edition of ANSI / AF&PA SDPWS-2008 Wind & Seismic - Special Design Provisions For Wind And Seismic, after reading through the necessary sections of 4.3.6 Construction Requirements, I don't see a requirement for the number of gypsum wallboard layers.

Conservatively, I will use (1) layer each side of wood stud wall.

Does anyone know where I can find the requirement for number of gypsum wallboard layers? Did I miss it?

Thank you!

 

[msquared48]

Structurally, using only one side is ok, although most walls have gyp on both sides for finish or fire.

Mike McCann, PE, SE (WA)

 

[mike20793]

You can use a 2-ply on each side. It's buried within the shear wall values for gyp board; they have a section for 2-ply 5/8" gyp board. As far as I know, that is the only assembly for multiple plies that has been tested. I use it frequently for fire separation walls that act as shear walls.

 

[BadgerPE]

Mike,

When using (2) layers for fire separation, what is your diaphragm attachment like? I have run into this issue on multi-level construction where the gyp needs to go to the roof deck, but there are floors that need to frame into the shearwall. Just curious how others handle this.


OP sorry for the hijack...if you want to flag for removal, I understand.

 

[mike20793]

I've only had one project that was multistory and had fire separation walls. They were party walls, so the architect placed the two layers of gyp board (each wall) between them. This way the floor framing didn't interrupt the gyp board. I've heard nightmares of 2 hour rated single walls that support the floor framing and how to deal with it. The result was either fire retardant treated lumber mixed in with the gyp board or some funky balloon framing.

 

[jayrod12]

Mike,

How did the framers drywall the gap between party walls? Anytime I've seen that detail it's been people laughing about how you can't sheath the faces of party walls at the gap.

I just don't see how you get the fastening correct, or tape the joints (as is required by fire code I thought).

 

[mike20793]

I'm not sure how they did it for the fire rating. We sheathed the inside of the unit when they were shear walls to avoid that specific issue.

 

[msquared48]

Well, if I have to go to two layers of gyp for shear, I go to one layer of plywood with gyp over if required. If a party wall, the plywood can be placed on the inside of the wall unless the 2x4 studs are staggered on a 2x6 plate.

Mike McCann, PE, SE (WA)