Wall stud spacing

[I-beam]

I have a 2-story wood framed building (Condo)with 30' roof trusses
and floor joists spanning 15'. Can the roof trusses be spaced
at 24"oc and the floor joists and 2x6 wall studs spaced @ 16"

By the numbers, with 42psf roof snow load, I need 3-2x6 top plates (SPF #2), but most contractors
insist the triple plate isn't required. I can see the argument if the
plywood sheathing is considered as working with the top plates to carry
the truss spaced between the studs.

Any thoughts on this ………

Thank you

 

[NorthCivil]

The numbers might not crunch but you'll likely be fine. I would guess this is often overlooked by a lot of engineers.

I spent a few years doing strictly alterations in an old part of town. I still can't believe some of the things I've seen wood do, and do for decades (or even centuries).

42psf isnt all that high of snow load. like you say, the exterior sheeting, the interior drywall will help.

If the plate does begin to bow, load always follows the stiffest path, once the plates start to deflect, the load will shift away to other trusses, some of which will land on studs.

 

[msquared48]

OP: You posted the same question twice in this forum on the same day. Please eliminate one of them.

Mike McCann, PE, SE (WA, HI)

 

[DaveAtkins]

I struggled with this same issue when I was designing wood framed buildings.

I think you are on the right track. The exterior plywood or OSB will certainly help. Also, the nailing (and friction) between the two top plates will make them something more than two independent plates--probably not fully composite, but you get the idea.

So, the typical trusses should be OK when they bear midway between studs. However, be sure to put built up studs under girder trusses and the like.

DaveAtkins

 

[phamENG]

I'd stick with the math. Are wood allowable stresses incredibly conservative? Yes, unless you get a bad batch of lumber. Will the sheathing contribute to your plate stiffness? Yes, so long as it isn't VE'd during construction or some gimcrack alternative material is substituted. If it's not called out as structural on the plans, then it's fair game. I've had contractors take the position that, even though it was called out on the structural plans, it wasn't a shear wall so it didn't matter.

Will the building "work" with a double top plate. Probably. It's also unlikely that it'll ever see a true design event, but we design to that anyway - don't we? If you decide "it'll be fine" and then it for some reason it isn't, when calculations can clearly show the allowable stresses under design conditions exceed allowables....your a$$ is grass, my friend.

Can those contractors/owner show you that the loads for the buildings they're talking about are equal to or greater than the current building being considered? Can they show you calculations that you can't find fault with that show the allowable stress in the top plate isn't violated? If the answer is no, I'd not be in a hurry to put my neck on the line for them.

Maybe I'm being over conservative here, but given some of the poor quality I've seen in wood construction I think it's a reasonable stance to take.

 

[dhengr]

I-beam:
Use a better grade of 2x6 for the double top pls. Order them in long lengths to minimize splices and so as to distinguish from misc. blocking mat’l., to be cut up for the fun of it. And, isn’t there actually a stress increase allowed for 2x lumber, in bending, when used on the flat. As long as you detail it properly, the plywd. sheathing can assist the top pls. in bending and in getting the roof loads down into the studs, and for hold down too. I believe 4x9 plywd./OSB sheathing is fairly readily available. Also, it seems to me we’ve done those kinds of roof spans and snow loads with double 2x4 top pls. on the bearing walls in the past. I do remember running these calcs. a few times, rationalizing these details, to match a grade of lumber we were now using. And, that could be appropriate for you too, with the reductions in allowable stresses in new grades of lumber.

 

[BridgeSmith]

This is probably a dumb question, but can you put the wall studs @ 24" oc?

Rod Smith, P.E., The artist formerly known as HotRod10

 

[EZBuilding]

As soon as you put the wall studs at 24" off center the contractor will find a reasons to space the roof members 12 inches off of that.

 

[Celt83]

are you checking the top plates as a single span beam between studs or a continuous beam over several studs?

My Personal Open Source Structural Applications:

https://github.com/buddyd16/Structural-Engineering

Open Source Structural GitHub Group:

https://github.com/open-struct-engineer

 

[BridgeSmith]

Yeah, you're right EZBuilding; shoulda known that...as I expected - dumb question.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[KootK]

This is probably a dumb question, but can you put the wall studs @ 24" oc?

You can and that's basically the whole "Advanced Framing Business": Link. Of course, for it to work, everybody has to be on board and can't be allowed to change their minds part way through.

 

[Agent666]

In this part of the world if you're more than 150mm off a stud you need to provide another mini lintel between studs to support a truss. Suggest you simply provide a detail showing something similar with limitations on when it's required and when they can bear directly on the typical continuous top plate as a means of ensuring you don't end up with a 12" offset.

 

[XR250]

I have never seen this as an actual field issue in my 29 years of inspections. Personally, I would not worry about it - guarantee your competition down the street ain't.
Got to pick your battles in wood construction.

 

[AaronMcD]

Are you using hurricane ties to hold down the trusses? How to attach those if there isn't a stud? Is the top plate to stud connection sufficient for uplift?

http://www.hellodwell.design