Construction Plans: How to Improve Clarity of Framing Lumber Specifications

[FrankWoeste]

A simple specification such as No.2 KD-19 XYZ-species may no longer clearly communicate to other parties what products and design values were assumed and used by the RDP in their design work and thus required for the project. For example, see 2024 NDS Supplement, new Table 4G, starting on p. 63 for lumber made in the U.S. and around the World at the AWC website:

https://awc.org/pdf-viewer/?idp=1413&idf=4

The authors suggest a more robust specification as published in the Structure Magazine:

https://www.structuremag.org/?p=23897

Your comments are valuable and greatly appreciated.

 

[phamENG]

That's a bit concerning....Southern Pine with a G = 0.35??? I can barely count on a contractor to buy Southern Pine rather than SPF, and now that southern pine might be shipped in from over seas with a G even lower than SPF? Most in wood construction have no idea what any of these values mean (including some engineers), so I'm very worried that "Southern Pine with Specific Gravity of 0.5 or higher" isn't going to help much.

How can it be grade marked as Southern Pine if it has a G value so low as to cut connection capacities almost in half? I must be missing something here.

 

[FrankWoeste]

I understand your concern. We covered these issues in our VT May short course and suggested a way to make a more robust lumber specification in your plans. Assuming you used and want to specify 2x4 wall lumber listed in the NDS Supp. Table 4A, instead of using the typical spec such as this:
"All wall framing lumber shall be 2x4 KD19 No.2 SPF or Btr."
consider this spec:
"All wall framing shall be 2x4 KD19 No.2 SPF (Fb/875, Ft/450, Fv/135, Fc-perp/425, Fc/1,150, E/1.4, and G/0.42) or Btr."

Assuming you used and want to specify 2x4 No.2 KD19 Southern Pine wall lumber listed in NDS Supp. Table 4B, consider the same format:
"All wall framing shall be minimum 2x4 KD19 No. 2 Southern Pine, with minimum reference design values of: Fb/1100, Ft/675, Fv/175, Fc-perp/565, Fc/1,450, E/1,4000,000 and G/0.55."

Do you feel the longer format including the NDS Supplement tabulated allowable design values strengthens the specification for all parties involved in the construction process?

 

[Aesur]

Here is an idea... stop allowing the importation of horrible lumber by codifying the lower properties. The codes are supposed to create an industry standard and by constantly updating and/or allowing inferior products all they are doing is putting the increased workload on the EOR, almost always without an increase in fee to offset the additional time (little things here and there add up fast on projects). I plan on just making a typical detail that has all the properties for the lumber I design and putting this on my drawings as a standard, however this is just another detail needed because of a code update. I'm not sure how it will be verified as I have yet to see a wood spec sheet shop drawing and if I start requiring that it will piss off contractors or most likely just be ignored. And we all know how there are many engineers still using much older codes based on knowledge and ignoring much of the newer code provisions.

Not only can this now be an issue, what do you do when there are no uplift connectors rated/tested for lower SG's. As soon as we start specifying the stronger lumber, which we have all been using per the code for a very long time, we will be the ones dealing with the complaints from the contractors and owners because their structure is more expensive because of this.

How will this be addressed in currently adopted, older codes; or even for projects that are already in construction using older codes but potentially using this inferior imported lumber.

This is IMO another example of code writers being out of touch with the industry and allowing for or pushing for changes to codes that have real world impacts without consideration for all the possibilities of their code change/amendments. Semi-joking - who was paid off for this code update allowing inferior lumber to be imported and used .

 

[FrankWoeste]

As a point of information, the lumber listed in Table 4G from around the world is graded and manufactured to the same PS 20 American Softwood Lumber Standard that is referenced in our U.S. building codes (IRC and IBC).

 

[ChorasDen]

I really don't understand why this was posted in multiple forums. With that said, I don't fully understand the argument that is being made here. If additional clarity is needed regarding the material used for framing and/or during specification, then the visual grading agency must make that clear on the product stamp. Indicating xxx Fb, xxx Fv, xxx SG means absolutely little to the field, particularly because the framer and GC does not understand it, and the lumber seller very likely would not understand either, so the addition of this requirement does not seem to me to fully hit the intent of the author's article. I would prefer clarifying the grade stamp.

 

[phamENG]

Aesur - ChorasDen or Dr. Woeste (assuming this is the Dr. Frank Woeste of VT) can probably speak to this better than I can, but the NDS supplements are less "code" and more a retroactive representation of what's out there.

Dr. Woeste: no, I don't feel the longer form is very helpful. I do use that for composite lumber to make sure I have adequate LVLs, but a material spec sheet is easy to get for those. I've never received a sawn lumber material data sheet. And as ChorasDen said, it means nothing to anyone in the field. If you're working on a big 5 story wood job with a seasoned contractor, maybe. But most wood builds are far less sophisticated.

The additional specifications are going to end up as more of a CYA note than anything else, I'm afraid.

 

[ChorasDen]

Thanks pham, to Aesur's point, this is a bit outside my area of expertise, having never sat in on an AWC committee meeting about this topic, but I might argue that I don't believe the code writers are necessarily out of touch with the specification community, but instead, and I am guessing here, there is likely a realization that this product is coming into the U.S. market one way or another, and it is best to qualify this product the best we can with the available information, even if that means publishing lower design values, rather than having a dearth of unqualified and uncodified wood in use for framing.

 

[FrankWoeste]

Well stated, ChorasDen.

As mentioned earlier, another design issue is published fastener and connector adjustments factors for G less than 0.42. While preparing for VT short courses, I reached out to two of the leading fastener and connector manufacturers and they kindly sent the information needed to adjust their tabulated values for the cases of G less than 0.42. You can view the SST adjustment information here:

https://ssttoolbox.widen.net/view/pdf/pqvsvpxr5l/C-F-2023TECHSUP-p023.pdf?t.download=true

and for Connectors here:

https://ssttoolbox.widen.net/view/pdf/yf0tka1rqn/L-ALTSPECIES23.pdf?t.download=true&u=cjmyin

 

[Celt83]

I'm not entirely clear on what the issue is, using a grade/species combination outside of what is called for in the drawings constitutes a substitution that typically would require review and approval.

"...instead of using the typical spec such as this:
"All wall framing lumber shall be 2x4 KD19 No.2 SPF or Btr."
In my experience that isn't the typical spec at all, typically wood is handled in the general structural notes with one note covering the moisture content at installation and a table or list of species/grades by application. "or Better" is almost never utilized as it gives too much freedom to the contractor/supplier and instead "or an approved alternate" is noted.

Perhaps I'm not understanding Table 4G as well, is this table stating that imported lumber can be stamped and sold as if it was the lumber from table 4A through 4E? If that is what is being allowed then I'd say the grading needs to be revised such that the imported lumbers meets or exceeds the North American Species values, lumber with lower properties should never be allowed to ship under the same stamp.

 

[gte447f]

Agree with Celt83.

Personally, I will not entertain allowing this lumber in my designs or on my projects. I will not change my specifications to include design values. To do so just adds more work for me, and as others have said it doesn't accomplish anything because lumber stamps don't list design values, so there is no way to verify. I will change my specifications to explicitly exclude multi-species combination stamps and any non-North American species stamps.

Interesting that the Structure magazine article sites the last 20 years that this non-North American lumber has been arriving in the U.S. construction market. I first saw these stamps in the wild about 4 years ago, right after... you guessed it... Covid 19. That's when this really became a problem, when the North American lumber mills fell behind due to Covid, and the construction industry turned to overseas imports as a cheap, emergency substitute. Now no one can put the genie back in the bottle.