Partywall Suability at Stairwell Openings (wood frame)

[Signious]

Hey everyone,

I'm wondering how you account for loading at tall, interior party walls for residential construction.

By Canadian code all party walls must be able to take 10psf without structural failure of the wall or any supporting members (ULS), this accounts for fire fighting equipment (ie. water) hitting the wall.

Now, do you consider deflection as a failure mode? I have been, but the more I think about this - the more I want to ignore deflection on these.

-If the wall works to support the roof without gypsum sheathing, and while it is deflected it has served the purpose(assuming once the wall deflects & water hits it the drywall is toast).
-As long as the wall deflects less than an inch it isn't going to hit the neighbouring wall, and if it does you get more rigidity.

The only arguments against this I can think of is after a fire they might have to rebuild the wall completely if the studs are damaged from excess defl'n, and of course saying code is code, and L/360 is your absolute under these conditions.

Thoughts?

edit: Common example of this would be a multi-family where a unit has a stairwell opening on an interior wall adjacent to another unit

 

[jayrod12]

I can comment on your common example,

I usually have negotiated OSB into the equation in all of my stair well walls behind the drywall. This provides significant increase in durability, strength and just overall confidence.

How tall of a wall are we talking that 10psf is causing excessive deflections? Unless you're neglecting any lateral support from the stairs/landing or floor systems.

Just because the stair openings are just shown as a hole in structural plans, the stair landings provide more than enough lateral load transfer.

 

[Signious]

Usually I will call for blocking & connection to the landings to help out, this is just a problem wall
-14' span
-10'1" floor heights the whole way up (main, upper, loft)
-16" deep parallel cord trusses

I like the idea of throwing some OSB between the wall & the drywall, hadn't thought of that.

That being said, when I went through my mentorship in wood construction It was hammered home to me by both of my gurus not to account for lateral bracing from stairwell platforms - they both acknowledged that they do provide some support but unless you quantify it, it is 'bad' engineering. Kind of on the 'it just works' idea train.

Do you put numbers to walls where bracing is depended on by the platform or only account on it when it is close?

edit: Not trying to rock the boat, I just like to fully understand!

 

[jayrod12]

I treat it like the ace up a sleeve, only pull it out if you need it. If they are in significant need of support then I find another way around it, horizontal wind beams at the floor plates and the like.

It's no different than blocking. Especially considering they are concrete filled steel pan stairs on all of the ones I've done. There is more than enough capacity in the landing framing to act as blocking between the walls.

I would make sure it needs to stand up for the 10psf (i.e. deflection doesn't matter) but make sure deflection works for 5psf (my average internal wind pressure).

 

[Signious]

Thanks jayrod