variation in lumber dimensions

[Lion06]

I'm working on an existing building that has number 3 lumber. The depths are all over the place - 2x12's range in depth from 10.5" to 11.25" Is this a function of the poor grade of lumber or is there something else?

 

[MikeHalloran]

I'm guessing it was built from mixed inventory, during the period when lumber went from x5/8 X y5/8 to x1/2 X y1/2.



Mike Halloran
Pembroke Pines, FL, USA

 

[ToadJones]

Weird.
In twenty years I have never seen a 2x12 less than 11.25"...give or take a few 1/16ths.
I have worked on some old buildings that had hardwood lumber 2x12's that were actually 2" x 12".

 

[msquared48]

Actually, in talking to a long time framer friend of mine a few years ago, he much preferred TJI's to the solid sticks for his floor joists as the depth varied as much as 3/4" between joists, raising H*&6 with his wall plates and floor level.

This is nothing new SEIT.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[Lion06]

Mike-
Aside from the getting them to be level, this amounts to a 23% difference in I, and a 15% difference in S. That seems significant to me! Doesn't the AF&PA (or whoever is in charge of this) have dimensional tolerances that need to be met? Is this true for any grade of lumber - that it can really vary that much?

 

[ToadJones]

In framing houses for 10+ years (1990's early 2000's), and even my own hosue a few years ago, I never used #3 lumber. Not once.
I can say for #2 SPF and SYP, I never saw variations on that level.
Mike-If you are talking about I-joists, yes, I much preferred them as well. They saved a lot of time. Often times they were made to span front to back on the house eliminating the lapping of conventional lumber. They had electrical knock-outs, the top flange was much wider than 1.5" making sheathing a breeze, nailing them to the sill plates was a breeze...etc, etc. etc. But, When the price OSB shot threw the roof a few years ago, they disappeared, and so did I from framing.
Not behind desk rotting

 

[ToadJones]

Also, in my own house, I didnt notice that one SYP joist had a more severe crown than the joists to either side....the crowned joist landed directly along a grout line in a tiled area. It almost looks like an optical illusion. To this day it drives me nuts. The floor is crowned 1/4" in 4'. I am somewhat lucky that it landed on the grout line, allowing the tiles to slope up to the raised portion on either side. Having it land in the middle of a tile would be a real pain.

 

[msquared48]

SEIT:

It got to the point, and he was using HF#1 or DF#2 material, that he had to rip the joists to the least common size, so your strength and deflection concerns are very valid. You can tolerate 1/4", but not 3/4.

Time to generate new span-load tables!

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[DTGT2002]

Do you have a set of plans indicating 2x12's?

Have you confirmed grade stamps on the lumber?

I am assuming you are talking SYP. Flipping quickly through the grading guide gives no such latitude to have a #3 2x12 be anything less than the 11.25" minimum.

Maybe you have a fat run of 2x10's?

 

[Lion06]

Yes, there are existing drawings (very scant) that call for 2x12's. No grade is called out, but Hem-Fir No. 3 was used - we did find the stamp on a large number of joists.

 

[Ron]

SEIT....the grading rules do not allow for much variation in dimension, just in the wood defects per grade. Do you know which grading rules were to be followed? Lumber grading for construction goes back to about 1920 or so.

Check to see if some of these were ripped for clearance of something.

I agree...that's a lot of variation. Even in older buildings, that would be a bit unusual. As TJ noted, lumber is not usually undersized.

 

[woodman88]

When lumber is cut green than drys you have shrinkage. Per the Timber Construction Manual 4ed, Hem-Fir will shrink Radial (3.5-4.5%), Tangential (7.0-9.2%) and Volumetric (9.8-13.0%). With #3 lumber the tree rings can vary height wise from radial to tangential. Which means the shrinkage values can vary from 3.5% to 13.0%.

It sounds like you may have a mix of dry cut lumber and green cut. With the green cut giving a 11.5"(1-.035)= 11.1" to 11.5"(1-.13)= 10" dry heights.

Garth Dreger PE
AZ Phoenix area

 

[woodman88]

Sorry didn't check my input numbers should be "to 11.5"(1-.09) = 10.5" dry heights

Garth Dreger PE
AZ Phoenix area

 

[BAretired]

I haven't run into this situation very often, but I do remember one residence where the lumber must have been very wet when it was shipped to the site. The 2x10 joists all shrunk approximately 3/4".

BA

 

[archeng59]

SEIT, how long ago was this building constructed? I've worked on buildings constructed in the early 1900's that have dimensional variations similar to what you describe, but those buildings were constructed long before grade stamps were used.

 

[Lion06]

It's about 40 years old.

 

[msquared48]

At 40 years ago, 2X12's were 11.5" deep, if cut from dry lumber.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[Lion06]

I looked closer at the stamps, and it says "S-GRN", so the moisture content was high. I believe that this really is just from shrinkage. I also found information that shows that the decreased MC, while reducing the section properties, has a net effect of increasing teh capacity because of the increased structural properties associated with the lower MC. This is true, down to about 10% MC.

 

[msquared48]

There you go...

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask