Choosing whether to decrease stud spacing or increase lumber grade for wooden stud walls

[SoleSteel]

First post

I have recently started designing wooden stud walls using Woodworks Sizer. For a basic interior 2x4 wall, I start out with 2x4 DFL Stud Grade @ 24" on center. Oftentimes, these parameters aren't sufficient due to one criterion or another and I have to either decrease the stud spacing or increase the lumber grade. How should I make the judgment whether to decrease the stud spacing or increase the grade of lumber? Is there a reason to prefer tweaking one parameter over the other with respect to cost, constructibility, and the different design values?

(Part of the issue is that I'm a chemical engineering grad converted to a structural Engineer-In-Training so I'm still learning the theoretical side of structural design. I do want to learn though!)

 

[Archie264]

16" is the most standard stud spacing I've seen so start with that.

 

[allgoodnamestaken]

Market availability, requirements for things in/through the wall (penetrations, utilities/services) that your tighter space might make difficult, deflection issues with wide spacing that may negatively impact servicability or the durability of surface finishes, etc etc

 

[dhengr]

SoleSteel:
16" o/c is mighty common stud and framing spacing for light wood framing. Many std. details and conditions work around and because of that spacing. Going from 2x4's to 2x6's at 24" or 16" o/c allows for wall load increases and accommodates vent stacks and other mech. equip. a bit better and also allows for improved insulation thickness. 24" spacing usually means that you want to start to stack the framing in continuous vert. lines or you will have trouble with top plate loading, etc. Changing lumber grade in the same location/area or on similar conditions and details might be asking for trouble, because there is a 50-50 chance that the builder will use all the good stuff in all the wrong places, unless you provide very explicit direction, management and inspection.

 

[jeffandmike]

Have to agree with Archie264. 24" on center stud spacing is generally not a good idea. You also begin to run into other issues such as potentially excessive (or even just undesirable) flexibility of the applied finishes when out-of-plane loads are applied. With a single 2x4 stud at 24" on center, have you checked perpendicular compression (crushing) of the plates (not to mention the ability of the top plate to span between the studs)? If you have a heavier girder reaction being supported, for example, crushing can be definitely be an issue.

After concluding that it's a good idea to start with 16" on center stud spacing, I would then look at a readily available, lower grade of material for the area in which the building will be constructed. It's not a good idea to rely on the contractor to notice that a higher-than-standard grade of material was specified... again, they'll either miss it altogether or put it in the wrong place. Any "savings" in material being specified will be eaten up by mistakes/additional labor, assuming someone actually notices a mistake was made. Keep it simple.

 

[mike20793]

I have had multiple contractors tell me that difference in price between stud grade and number 2 grade is less than 10% (for Southern Pine, Spruce-Pine-Fir, and Doug Fir). After that, the difference in grades is around 20-30%. That being said, I never go above number 2 grade. Studs at 24" spacing can be done and are done frequently in my area, but they require just a little extra attention because of the reasons listed above.

 

[XR250]

Do the calc by hand and the numbers will be more favorable :>

 

[dcarr82775]

Stud spacing is also driven by the floor joists. If using TJI's at 16" for the joists then stud spacing of 16" makes sense. If using wood trusses at 24" you can run into trouble with top plate bending, especially on multi-story buildings. That can drive you to the 24" stud spacing. I often go with 24" studs at interior walls and 16" at the exterior. Like everyone else said, you need to run the numbers and make sure things work.

I pretty much call for #2 HF or DF. The low crushing strength on HF can become problematic and often drives me to DF. SP isn't used in my area.

 

[medeek]

In my locale I always try to go for DF lumber. I typically call out 16" o/c and in extreme cases go to 12" o/c. However, before I do that I upgrade to DF No. 2 lumber. I usually never go beyond DF No. 2 for studs since cost will probably become prohibitive and availability may also be a problem. For tall stud walls I will also move to 2x8 studs before I go to a 12" o/c spacing.

A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com

 

[SoleSteel]

I had forgotten my password for a while, but huge thanks to everyone who replied. This was very insightful and helpful!