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Designing workshop to meet code with locally milled 'visually graded' 2x8's

Started by chainsaw_louie, March 16, 2013, 02:08:28 PM

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chainsaw_louie

Hi Fella's,

I am designing a workshop and trying to use my own lumber AND meet building code specifications for allowable spans.
My mill (Lucas 825) can easily cut 2x8's and with effort can cut 2x10's or larger.
As I already have 2x8's cut and dried, I would like to frame the workshop with 2x8" x 12' max, joists & rafters.

So I consulted three documents to see if 2x8's can be used:

a) for specs on poplar and northern red oak (my wood) I found  "Design Values for Visually Graded Dimension Lumber" http://www.cecalc.com/WoodDesign/Graphics/Wood_Reference_Design_Values.pdf

b) for allowances for spans of 2x8's  "American Wood Council SPAN TABLES FOR JOISTS AND RAFTERS" http://www.awc.org/pdf/STJR_2005.pdf

c)  and finally, a tutorial to understand how to use the above documents to figure the allowable spans: "AWC Understanding Loads and Using Span Tables"
http://www.awc.org/technical/spantables/tutorial.html

The thing is that the tables rate different values for the lumber's bending design value according to which grade it is:

  • Select Structural
  • No.1
  • No.2
  • No.3
I would like to use the 'select structural' or 'No. 1' values for wood strength as these are the higest, but I am not sure if I can, maybe nobody cares for a 'accessory structure' .

Am I on the right track , using the above documents to design my building ?

Thanks a lot .

(ps, if you dont want my stick framing post in the Post & Beam, forum, feel free to toss me out ! to the correct place for this topic :)  )

jueston

those all seem like great resources but it has been my building experience that only one thing matters, what your local inspector will approve... if you live in a area that has codes and inspections then all that matter is what he will sign off, if he is a good one, then you can call him up and talk these things through and find out what will pass...

if you live in an area without codes and inspectors, then its a whole different game, and you need only design for strength and rigidity, and your own satisfaction.

chainsaw_louie

We do have codes, inspections and an inspector here .  I was wondering though if it would be a good to even mention using homemade lumber and just submit  the plan.  The thing I worry about is that they wont know what to make of non-commercial lumber and if I ask, then he will have to investigate , but wont any point of reference and will deny it cause its easier and less risky etc .  Otherwise , if  I don't ask,  he may just look at the framing, see that it matches the dimensions on the plan and approve it.  But yeah its probably best to mention it in advance.....if there is an issue best get it out in advance.




jueston

You mentioned plans, did an architect draw these? if the architect notes rough sawn visually graded lumber then the inspector can't do anything but admire it.....

Ianab

Quote from: jueston on March 16, 2013, 06:44:32 PM
You mentioned plans, did an architect draw these? if the architect notes rough sawn visually graded lumber then the inspector can't do anything but admire it.....

Depends on YOUR local regulations, but getting an Engineer or Architect to sign of on using "ungraded" wood is one possible way around the regulations.

Chances are your home sawn wood is superior to store bought stuff, but it's a matter of PROVING that it's up to standard. A common approach is to just upgrade the building plans, use a larger size, or closer spacing, and then specify "ungraded" wood.

But getting an official stamp on your plans might be the way to go.

First step is to talk to the inspector though. He's the one with the final say.

Ian
Weekend warrior, Peterson JP test pilot, Dolmar 7900 and Stihl MS310 saws and  the usual collection of power tools :)

jwilly3879

One of the other hats I wear to support my logging habit is Building Inspector. Rough sawn lumber is allowed in most jurisdictions in NYS but you will need a letter from the sawyer that the lumber meets the grade of #2 or better. I would definitely talk to your code official and go over your plans with him. If this is a residential accessory structure under 1500sf you do not need plans stamped by an engineer or architect but you still need plans. The code official will review them and point you in the right direction if need be. He cannot tell you what to build it with (liability issues) but he can tell you what doesn't work.

Jim_Rogers

Quote from: jwilly3879 on March 16, 2013, 07:51:16 PM
One of the other hats I wear to support my logging habit is Building Inspector. Rough sawn lumber is allowed in most jurisdictions in NYS but you will need a letter from the sawyer that the lumber meets the grade of #2 or better. I would definitely talk to your code official and go over your plans with him. If this is a residential accessory structure under 1500sf you do not need plans stamped by an engineer or architect but you still need plans. The code official will review them and point you in the right direction if need be. He cannot tell you what to build it with (liability issues) but he can tell you what doesn't work.

Thanks for posting this.

I knew there was some rule in NY about the sawyer statement of quality but I wasn't completely sure how it works.

Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

jdtuttle

Like Jwilly I too am a building inspector to help support my sawmill habit. Here is the code on using rough cut lumber in residential construction for NY. I also included a link to NY res. Bldg. codes. NY now uses a perscriptive code & there are span tables there. The Building inspector also has to allow rough cut, some do, some don't. I do though  :D   http://publicecodes.cyberregs.com/st/ny/st/b400v10/index.htm

R502.1 Identification. Load-bearing dimension lumber for joists, beams and girders shall be identified by a grade mark of a lumber grading or inspection agency that has been approved by an accreditation body that complies with DOC PS 20. In lieu of a grade mark, a certificate of inspection issued by a lumber grading or inspection agency meeting the requirements of this section shall be accepted.

Exception: Dimension lumber which is neither identified by a grade mark nor issued a certificate of inspection by a lumber grading or inspection agency may be used for load bearing purposes under the following conditions when authorized by the authority having jurisdiction:

1. The producing mill shall sell or provide the lumber directly to the ultimate consumer or the consumer's contract builder for use in an approved structure.
2. The producing mill shall certify in writing to the consumer or contract builder on a form to be provided by the authority having jurisdiction that the quality and safe working stresses of such lumber are equal to or exceed No. 2 grade of the species in accordance with the conditions set forth in American Softwood Lumber Standard (PS 20-99) published by the United States Department of Commerce. Such certification shall be filed as part of the building permit application.
Have a great day

beenthere

And it will take some nerve for the producing mill to make that certification if they look at the liability. But hope they still will go ahead and take that chance.
south central Wisconsin
It may be that my sole purpose in life is simply to serve as a warning to others

Jim_Rogers

To the original poster:
If you have studied the actual grade rules, and your lumber meets Structural select grade rules then you as the sawyer could/maybe able to fill out the paperwork and submit it to your building inspector.

However, you may have to prove to him that they truly do. Structural select has some very strict grade rules and I hope your lumber meets them.

We normally try for Grade #2 or better. And design for those values from the beginning.

Adjust your spacing or distances to make grade #2 pass the load checks.

Good luck with your project.

Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

chainsaw_louie

Thanks for all the useful feedback.  I see that I have to design this thing in reverse, starting with the code requirements.
Using the deflection allowances for joists ,  I can see that the L360 is the deflection required for a 2nd floor that isnt an attic:



 

Next, the loading definitions for a room that isnt a bedroom is going to be 40 psf and for the 'dead load'  a minimum of 10 psf:


 

Using the table from the AWC, to get the 'Bending design requirements Fb'  , I looked at this table and see that the bending values are the same regardless of what size of joists are used 2x6 , 2x8, 2x10 etc. Not what I thought but more importantly is the Fb numbers:
---> 718 for joists 12" oc
---> 790 for joists 16" oc



 

My Yellow Poplar will barley meet those requirements and only if I space them 12" oc:


 

On the other hand, if I use the red oak , then I have joists that have higher 'Bending Fb' numbers,  800-975 for the conservatively graded No.2, depending on whether its 'mixed oak' or 'Northern Red'  (who can tell after its cut and dried?)


 

So this is now going somewhere....the table below tells me that if my red oak joist has a Fb value of 900 then I should be allowed to use 2x8's with a clear span of 10'7" and 16" oc,  I can live with that


 

Those floor joists look to be the most stringent deflection requirement.  Next would be the 2nd floor ceiling at L240 and finally the roof rafters (with greater than 3/12 pitch)  of L180.  For these , the yellow poplar may work for these.  Got to check.



S.Hyland

Swampfox, I feel for Eustace Conway. Everything I want to do seems to be illegal too!  Hoo boy I'm suppress the coming rant right now.  smiley_furious3
"It may be that when we no longer know which way to go that we have come to our real journey. The mind that is not baffled is not employed. The impeded stream is the one that sings."
― Wendell Berry

chainsaw_louie

I just found this calculator on the AWC site that seems to provide all the span and flex data for a given species and dimension of wood.
But the values it puts out dont seem to match the tables, I must be missing something because their calculator says No.2 Yellow Poplar has a bending strength of 966 psi but their table says it only has a Fb rating of  716 psi:

calculator==> http://www.awc.org/calculators/span/calc/timbercalcstyle.asp



 

hmmm, somethings up because that value does not match the published AWC value in here (page s36) http://www.awc.org/pdf/2005-NDS-Supplement.pdf
...and the difference between what the caluculator reports and the listing in the table for No.2 Yellow Poplar is quite large. Eventually I will have to go to an engineer but I'd like to make sense of it on my own , first .


 

Jim_Rogers

Have you read this post?

https://forestryforum.com/board/index.php/topic,50714.0.html

In here I explain the way an engineer will look at a frame and do the math to prove the timber are ok.

Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

chainsaw_louie

Thanks Jim, I read that posting, with complete and accurate  calculations of the dead load, live load and wood species and sizing, I dont think an engineer will find many surprises in my design. Its definitely a good path to follow . 

I sent an email to the AWC re the joist calculator discrepancy with the values in the tables and they told me about the two 'adjustment' multipliers:
   - add 15% for repetitive framing members
   - add 20% for 2x8's due to their depth

"Thanks for the inquiry. Bending design values are permitted to be increased by several adjustment factors as outlined in the Span
Calculator "Help" screen. One of those adjustments is the repetitive member factor, Cr, which is a 15% increase. There is also a size adjustment factor, CF, for 2x8s which is a 20% increase."


So, good news , my yellow poplar with a Fb of 700 just got increased to Fb=966  and can span 11'3" at 16" oc

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