Extending existing exterior wall

[strucitright]

Got one I have never done or seen before and would like a check of my work if possible.

The job is for an addition and to increase the story height. They want to keep part of the 4' pony wall as a lower roof section is connecting to it, and would prefer not to build inward as there are space constraints. Shear is taken by the addition.

So existing 4' 2x4 wall proposed to raise to 9' with 5' of new 2x6 walls.
14.6 psf wind @ 1.33' = 19.86 plf
Moment at 4' = 198.62 ft-lbs
Tension at each face = 198.62 ft-lbs * (3.5"/12)/2 = 1362 lbs

The inside face would have a steel strap. (detail attached)
The outside face tension would be taken by either a notched 2x6 (detail attached) lapped and nailed over the existing 2x4. An alternate could be twist straps but thought this was less likely to hinge.

My concerns:
-Dumb, expensive, and there is an easier solution
-Reentrant corner at the notch
-Missing something

Similar thread on 2x6 to 2x6 but much taller.

https://www.eng-tips.com/viewthread.cfm?qid=374884

 

[jayrod12]

I strongly dislike this. This has been discussed ad-nauseum on this forum, but there's lots of nail slip in those straps. Just put full height 9 foot 2x6s. You don't necessarily need to remove the old studs, you could just sister full height ones adjacent the existing. In fact, if I gave the local frames the option of 5 foot additional studs with straps, versus just new full height studs, they're picking the full height studs everytime.

 

[strucitright]

Thanks for your reply. I thought I did a good enough search.

That is the way I was leaning but this is a difficult client.

 

[jayrod12]

Is there a contractor on board already? If so, have them provide the comments. That's usually how I sell it to difficult clients. If there's not a contractor yet, plead with the owner and/or architect to call a contractor that owes them a favour and have them provide comment on the two plans. Notching the 2x6 is just added labour and wasted material. May as well just keep them un-notched and sister them to the existing 2x4. I don't understand why that isn't an option.

 

[Aesur]

Why not just lap the 2x6 studs full length to the 2x4 studs? Seems less complicated and if you are proposing notching the stud as shown in your detail why not just sister and lap them full depth, is 2" loss of space for the lower 2.5' going to make or break the structure, doubtful.

 

[strucitright]

I agree is it dumb and pointless. We are going to sister full heights as there is a better chance of "saving" more wall that way.

Part of me also wanted to solve the problem just to solve it.

One more question. There is a 8' dormer bathroom at the corner that was recently done. I have seen detail in the past for raising a wall 1' that showed full height studs at 8' on center and then a 6x12ish beam spanning horizontally the 8'. Not sure if I am buying it...

 

[jayrod12]

I could get behind something like that I guess, but I doubt that one stud every 8 feet could take the entire wind load from the entire wall. I assume the studs that aren't sistered can't just hang there in space.

 

[phamENG]

If you really want to convince them not to do it, just tell them it violates the building code. There are limits on on notching and boring studs. This detail violates them. Done.

Sounds like you may have already moved on to a more sensible detail, though, so just tuck it away for the next obstinate, penny wise-dollar stupid client you have.

 

[strucitright]

phamENG, Thank you for making it easy. IBC 2018 2308.5.9 and 2308.5.10.

jayrod12, 2 studs every 8' is what my calcs come up with (detail attached). The existing top plate would get toenailed into the new beam. This would as least let them work around their existing plumbing.

 

[strucitright]

phamENG, Sorry if that sounded sarcastic. I did not mean it that way. Thank you.

 

[phamENG]

Unless I'm in a really bad mood, I tend to take responses as positive. It has two benefits:

1) Prevents unnecessary "fights" with anonymous internet people who's opinions really don't matter to me all that much (there are a few exceptions on here, but for the most part they are not anonymous), and
2) If they are being rude, I get to 'kill them with kindness' as my dad used to tell me in middle school. (Didn't work for me then as I still go beat up, but I get a sick satisfaction out of it today.)

So you're welcome. I hope it really was helpful. And I apologize if my response came off short - I get really impatient when contractors try to push engineers to do stupid details that probably won't work past the warranty period (while we still have a solid 5-10 years left on the statute of limitations depending on jurisdiction) and violate the building code anyway.