LD1
Epic Contributor
As you have found out, it is pretty difficult to just find a generic chart that shows Fb, and E values of common graded lumber. But those are just one piece of the information.
It would be nice to know the anticipated wind and snow loads the engineer is designing for.....was well as the spans and spacing. Cause then you can simply plug those numbers into the calculator.....and choose the size, grade, and species of lumber you are thinking and see if its acceptable.
For example....when I built by barn....which was a common 2x6 stud wall on top of a block foundation....I also opted to add a little loft for storage. 8' loft. The "joists" for the loft needed to span 8' minus the triple 2x12 beam they were hanging on. So a ~7'7-1/2" span for the joist. So I was faced with a decision on how to do the joists to get to my design target of 100psf loading.
On 12" centers, a #1 SYP with 100# live and 5# dead load was rated to span 7'11"
#2 SYP was only good for 7'7"
#1 and #2 SPF were both only good for 7'7" as well.
IF I went to a 2x8,
#1 and #2 SPF would span 7'11" on 19.2" centers
#2 SYP Would only do 7'5" on 19'2" centers, so would need to drop to 16" centers to get 8'2" span
And #1 SYP would span 7'9" on 24" centers.
So armed with this info I could have used:
#1 SYP 2x6's on 12" centers
#2 SYP 2x8's on 16" centers
#1 OR #2 SPF 2x8's on 19.2" centers
#1 SYP 2x8's on 24" centers.
So there are many ways to skin the same cat and be okay. Higher grade lumber....different spacing, or upsizing from 2x6 to 2x8 or from 2x8 to 2x10, etc all has an impact on the final strength of the structure.
At the end of the day, I decided to go with the #1 SYP 2x6's on 12" centers. At the time they were actually cheaper than the standard #2 SPF 2x6's at menards, even though they were special order. Going with the 2x8's would have been more per board but needed fewer boards. SO it was a wash.....pennies difference. So I decided on the 12" centers so I could sheath the floor with cheap (at the time) 7/16 OSB rather than go to thicker OSB suflooring like 3/4" thick stuff.
I use that AWC wood calculator alot. I dont focus too much on the FB or E or any other designations for lumber "strength". Because those only tell part of the story. I input a set of parameters, select a board, and see its rated span. Choose a different board and look at its rated span. Because the rated span takes into account ALL the variables of the lumber. And if a board is rated to span farther, it can safely be assumed it is gonna be stronger than one rated to span less. Just like I have mentioned in your scenerio.....with 12' spans....enter some parameters. Then play around with 2x8 SYP #1 and #2, and SPF #1 and #2 and without changing the loading or any other parameter other than grade and species....and see which one is rated to span farther. For example....L/360, 40/5 psf live/dead, 24" centers.....2x8's.....
#1 syp = 11'2"
#1 and #2 SPF the same at 10'9"
#2 syp weakest at 10'2"
Thats what I meant by "play around with" that calculator.
Based on your spans, and a close estimation of loading....#1 syp is gonna be the strongest. SPF (either 1 or 2, no difference) is gonna come in second. And #2 SYP is the weakest. So if your engineer simply specs #2 OR BETTER SYP......well I'd classify both #1 and #2 SPF in the "OR BETTER" category since it is stronger/capable of farther spans
