Why does the NDS group SPF#1 and SPF #2 together?

[Ben29]

I specify SPF #1/#2 for wall construction. They are listed together in NDS Table 4A, and therefore have the same design values. A contractor sent me an RFI today asking if he could use SPF #2, and he gave me the below sheet indicating lower design values for SPF#2.

 

[Celt83]

The table they sent you is for Spruce-Pine-Fir (South) not Spruce-Pine-Fir.

Not only does SPF(S) have lower reference stress values but it also has a lower specific gravity which would mess with your connection designs as well.

I'm making a thing:

http://www.thestructuraltoolbox.com

(It's no Kootware and it will probably break but it's alive!)

 

[ChorasDen]

NDS design values are based on the grading rules set by the various grading agencies. Really your question should be directed at the grading agency, and how their grading rules lead to the published design values found within the NDS supplement.

 

[Ben29]

Thank you so much for pointing that out. Do home builders use SPF(s) interchangeably with SPF? Does the IRC specify that SPF should be used over SPF(s)?

 

[phamENG]

Do home builders use SPF(s) interchangeably with SPF?

Ha. Around here, contractors just use wood. The more refined will use either white wood or yellow wood. Start talking about Spruce-Pine-Fir or Southern Pine and their eyes glaze over.

 

[JStructsteel]

I would imagine they lump it all together to span the range for the wood. I think individual suppliers might break it down.
Specify SPF with the min values if you want to be specific.

 

[XR250]

I doubt you can even source #1 SPF (at least around here).

 

[dhengr]

Ben29:
Various species of wood are grouped together based on their general grain structure, knot size and structure, suitability for construction, density, etc, in the grading process. They make up a sufficiently large group/combination to be a saleable group. Otherwise, we would have 9000 smaller groups which nobody could keep track of. Each species may have slightly different grading rules, species specific, but generally they have about the same construction strengths and characteristics under those rules. When they are grading, they are grading only one species of lumber at any one time, at a mill. Then, they are grouped together for sale.