Tall Wall

[pdev67]

Happy New Year to All. Need help on check. Just curios to double check my load calculations. Practicing on a 38' long and 26' wide house with 2' roof overhang. It has a tall wall 20'(9' main floor+1'floor joist+10' upper floor). each floor has two window of size 132"x72". It is in Edmonton Alberta. I have taken Roof Dead load 15psf, snow load 37psf and wind load 17psf. So plf on exterior wall is, Dead load=15x(26/2+2)= 225plf, Snow load=37x(26/2+2)= 555plf.Total factored load = 1.25DL+1.5SL= 1.25x225+1.5x555=1113.75=1200plf(rounded) Total wall length is 18'. As the opening is 11' wide so the tributary width for load taken by king studs(built up common) = 5.5'+6"+6"=6.6' (half of opening+assumed with of 4ply column+half of stud spacing. Total factored load=1200plfx6.5=7800lb Is it correct?
What tributory width should I take for trimmer studs load calculations? if we see elevation of wall loads from the truss transferred to the top plates then through cripples to Lintel beam over the opening. Do I need to design trimmer studs for the 5.5' tributary with same load as for king studs or should I consider the load is transferred to king studs and check trimmers for bearing? Please advise

 

[dik]

You might want to check:

https://www.woodworks.org/wp-content/uploads/Tall-Walls-Workbook.pdf

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[jayrod12]

Is your wall 2 full storeys or does the second floor frame in?

 

[pdev67]

Thanks!
Jayrod12- it is continuous 20' high tall wall (2 full stories)

 

[jayrod12]

Does the second floor attach? Or is it in a great room type 2 storey open air area?

Provide a plan view and maybe a section through the wall so we can see what we're dealing with and you'll get more helpful responses.

 

[pdev67]

It is a great room rear wall open to above. I have attached the pdf

 

[jayrod12]

Certainly looks like you're on the right track for your load takedown then.

On a standard wall height I usually design the trimmers for all the gravity load, and the kings for all of the lateral, however on tall walls that isn't always economical. So in your case, I would be providing enough trimmer to suit bearing but don't look at trying to shrink that down if it's close to just over 1 1/2" or 3", go up a stud to a 2(or 3) ply trimmer so you know that you've got some capacity there. The fastening of the trimmers to the kings will also be of importance to ensure that the load does in fact get shared between plies.

I would be telling them that those 20ft tall walls would be significantly better off as 2x8 walls. Otherwise you're likely to end up with nothing but studs and no room for insulation. Just a shot in the dark guess here, but at 2x6 walls I'd bet you need a minimum of 2 trimmers and likely 4 kings. So you're at 9" of lumber on each side of each window. On the upper side you've got a floor beam framing in roughly what, a foot away, so you'll have another stud pack there and maybe end up with a couple inch gap between them. So in 24" of wall you'll have almost no insulation.

 

[Mike Mike]

I agree with Jayrod. One thing I would add is I've had contractors request to change from sawn lumber to engineered lumber studs for tall walls on several jobs. I believe the reason is sawn lumber studs are not straight enough because of warping. Can anyone confirm? On current jobs I save myself the potential CA questions and just give the contractor the option on my drawings from the start.

 

[jayrod12]

My experience is similar for going to engineered studs. Generally 1.3 or 1.5E LSL studs I give as an alternative directly on the drawings. They do typically appreciate the straightness of the engineered studs.

 

[pdev67]

I checked in forte software with above calculated loadings

For wall studs-20'
Current Solution: 1 piece(s) 1 3/4" x 5 1/2" 1.55E TimberStrand® LSL @ 12" OC PASSED

For Built up column-(4ply King Studs)
Option 1- Current Solution: 4 piece(s) 1 3/4" x 5 1/2" 1.55E TimberStrand® LSL FAILED- for deflection at mid span 1.57 where as allowed is 1.31
Option 2- Current Solution: 4 piece(s) 1 3/4" x 5 1/2" 2.0E Microllam® LVL PASSED

Based upon deflection ration can we add one ply to LSL and have 5 piece(s) 1 3/4" x 5 1/2" 1.55E TimberStrand® LSL ( as software does not work for 5 ply)
Now it is 7 ples (king+trimmer) For connections- can we use SDS screws 24" o.c from both sides??

 

[jayrod12]

Like I said, I'd really try pushing for 2x8 studs. They don't even need the full bearing, you can cantilever the studs over a support up to d/3 without an issue. You could maintain the inside face of stud dimension.

You'll end up with likely half the number of studs.

 

[racookpe1978]

2x8?
If 2x6 at slightly closer distances (if needed) were used, seems you'd be able to work more insulation in without insulation supports or sagging or needing some fillers between a 2x8 at 24 or 30 inches spacing.

 

[jayrod12]

2x8 at standard 16" spacing. So the insulation and blocking and all of those details stay the same. Look at his spec, LSL studs @ 12" o/c. They don't have pre-cut insulation for 12" stud spacing, so now you've got to cut every piece of insulation on that wall.

As soon as walls start getting near that tall, I just tell them outright that we're at 2x8 studs. No arguments no debate.

 

[racookpe1978]

Good point. Thanks.

 

[HouseBoy]

I thought LSL studs are 1 1/2" wide and LVL's are 1 3/4" wide.

Trying to sort out which loads you are asking about to be attributed to the trimmers (also called Jack studs?) and the King studs.

Seems like maybe you could say the Jack studs are carrying the gravity loads and King studs are carrying the wind loads.

I agree that 2x8 wall framing is appropriate for this condition. H/d is pretty dang high with 2x6 framing and it seems like that will affect the allowable ESPECIALLY in the combined load case.