Guidance on diaphragm front wall with very large windows

[Bammer25]

I have not looked too deeply into this before for residential construction. A client is using very large windows (see attachment) in series on top of each other. I am doing a simple deck design for them and they asked me to look into this.

I know the basics that the wall sheathing is my lateral load resisting member, and those windows just reduced my capacity a good bit. They used double 2x6 or 2x8 headers n between the windows. Does this need to turn into a full blown lateral stability analysis or

is there a rule of thumb?

 

[TORCHMAN]

I believe the rule of thumb in the Canadian code is that the wall cannot be more than 3.5 times its length to be used as a shear wall. In which case the walls adjacent to this window, assuming there is no floor at the midspan, cannot be used as a shear wall so lateral support would have to come from elsewhere.

 

[Bammer25]

There is a floor halfway up. That window is just in the stairwell. See attachment. I would think when you get to a certain size opening you just lose stiffness and could possibly make up some of that stiffness by adding framing around the opening?

 

[ChorasDen]

...possibly make up some of that stiffness by adding framing around the opening

How do you come to the conclusion that the end post will provide sufficient stiffness? Shear wall boundary framing does contribution somewhat to the stiffness of the monolithic design, but it's not the only part. Height/width ratio plays a much more significant part. Check the National Design Specification (NDS) Special Design Provisions for Wind & Seismic (SDPWS) equation 4.3-1 for more info. SDPWS also requires reduction in shear wall capacity based on height to width ratios that exceed 2, see section 4.3.4.2.

What is the LFRS for this structure? unblocked diaphragms and wood framed shear walls? If so, what's the distribution of forces to these shear walls, what the required capacity, can you achieve that with the narrow sections of shear walls and the reduction in strength associated with these walls? Would you be better served by considering a Simpson Strong Wall product or similar? These shear walls come as narrow as 12" wide, but you'll need to make sure you can resolve the overturning force at the foundation and check for pullout.

What is your role on this project? Are you acting as EOR? It sound like you may not be completely comfortable with lateral design, maybe best to turn this job over to someone with more experience?

 

[dhengr]

Bammer25:
And, on the back side that exterior wall is a three story high wall? Then it looks like almost every vert. stack of windows is also in a different wall plane, so you have no larger wall plane, a long run of wall, despite the small widths of vert. solid framing (sheathed framing) which might start to act like shear walls or frames. RE: the vert. window group you showed first; if that is in a stair well, how do you transfer loads at the 2nd fl. level, and is that a tall wall? Also, if those bot. two windows are in a stair well, they may have to be tempered glass, for fall protection.

 

[lexpatrie]

Traditionally this would be resolved with the International Residential Code and the braced wall provisions. It doesn't eyeball like that's going to work as there doesn't seem to be enough continuous wall (4' or so as a minimum). Particularly the middle piece if that sticks out more than 4' or 8' from the main building line on that elevation.