# Double 2 x 12 span



## Uncle Bob

Beam/Girder spans.  I have been talking to local framers in this new area and they seem to be of the opinion that if you sandwich 1/2 " osb between the 2 X 12s, you extend the span limit to 12 feet.  Without engineer's specifications I can't accept this.  Anyone heard of extending 2x12 lumber spans by using this method?

Thanks,


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## jar546

This method is not prescriptive.

If there is a joint in the span then the increase is negligible at best

PE's that I spoke with say it can add from 0 to maybe 4% depending on how and where, maybe more.

If they are under spanned prescriptively but point to this as an excuse, I give 2 options: 1) Meet the span tables or 2) Get a structural engineer to stamp it.


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## pyrguy

We did the sandwich thing not for spans but to get the double to match the wall thickness.


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## fatboy

I agree UB,don't buy it without a stamp.


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## Daddy-0-

People will also use foam blue board for the sandwich to get a little R value but the charts only recognize the framing members. Good catch.


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## kyhowey

Don't believe it for a minute.


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## codeworks

nope. gott a be an lvl beam or designed by engineer


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## jar546

This reminds me of another pet peeve.  Calling it a beam or girder prescriptively when there is a space between the members such as a deck that calls for a double 2x10 beam and they have one 2x10 on each side of a 2x6.


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## Pcinspector1

Agree with the others, LVL or engineer design.

In the old days they use to sandwich a piece of steel between the 2x's, don't hardly see that anymore?

pc1


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## Sifu

Right on Jar, split "girders" bothers me too.  Another thing to watch for is the practice of using thin strips of plywood at the top and bottom of a header, giving it the appearance of a solid piece.  I think an argument could be made that one could properly fasten a solid piece of pywood between two members and have them act as a single member however I think you can still only count on the values of the members.  And if they aren't fastened together properly you may be reducing the loads to less than the tables indicate.

The NC code acually has (or had as of 08) prescriptive flitch beam load tables for the steel sandwich.


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## Sifu

And, by the way, I used steel flitch plates all the time when I was building.


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## Kearney.200

I agree no Stamp no Go


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## jar546

Sifu said:
			
		

> And, by the way, I used steel flitch plates all the time when I was building.


We used them on garage headers all the time.


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## fatboy

And I'm sure they helped, last time I checked,  2 X 12's would not even make a 9' garage door span with a 24' bearing total roof span. But, even with the flitch plate, would still need engineering today. BTW, never seen a fliitch plate used around here, had just heard/read about them before.


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## elowpop

doing a review  without  information

How can any comments be made without any idea of the load. I see too many headers  where they are not bearing any load.


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## jar546

elowpop said:
			
		

> How can any comments be made without any idea of the load. I see too many headers  where they are not bearing any load.


Excellent point.  I guess we are assuming there is a load, otherwise, what's the point of the conversation.


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## north star

*# # #*

elowpop,



Welcome to The Building Codes Forum!  



*$ $ $*


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## Inspector Gift

Does anyone else use StrucCalc?   ...Uncle Bob?  ...Anyone???

2-2x12 DF #2 floor beam or roof beam spanning 12 feet with a 4 foot tributary load -- passes.


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## Uncle Bob

Inspector Gift said:
			
		

> Does anyone else use StrucCalc? ...Uncle Bob? ...Anyone???2-2x12 DF #2 floor beam or roof beam spanning 12 feet with a 4 foot tributary load -- passes.


Hey Terre,  

Nope, I don't do engineering; don't want to put those good people out of work. How do you know what the "tributary load" is? Why does the code table (2009 IRC, Table R502.5(1) restrict 2-2x12 douglas fur any # to not more than a span of 9' 9" where the building width is 20 feet; and only allows 7' 6" where the building width is 36 feet?

With your Struc-Calc; do we just tear the code tables out of our books and say a software program voids the code?

The code states that compliance with the code is required accept where spans exceed the limits of the code and then engineering is required. Terre, do you require code compliance or not?

Uncle Bob


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## mark handler

Inspector Gift said:
			
		

> Does anyone else use StrucCalc?  .


I do, span depends on loading....comp shingle? tile? point loading?


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## Inspector Gift

Great topic, and good questions, Uncle Bob...    As you know, the span tables in the IRC are not all inclusive.  Given a set of plans, we will check beam sizing with StucCalc if there is a concern.  And I will allow alternate methods and materials.  G


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## DRP

Which is according to accepted engineering practices, no differently than if I have the salesman check the same girder as an LVL or if I refer to the NHBA's flitchplate design tables; Flitch Plate and Steel I-Beams.

BTW in a flitchplate girder the steel is carrying the load, the wood prevents buckling. A flitchplate for a given load and span will I believe, always be heavier and thus more expensive than an I beam. When LVL's came out they largely replaced flitchplate beams.

In a <8' header you could add the section of the plies with grain oriented along the beam's axis to that of the solid sawn wood. If you're splitting that hair you're cutting it too fine. Once there are joints in the ply it's getting pretty deep.

As an aside and I'm curious. I worked with one seasoned old carpenter who would unroll flashing inside a girder between plies and have us nail it up tight. He claimed it made the girder stiffer. I think it was too thin not to ripple its way out of that problem but am not certain, the bottom strap would be reinforced.


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## Pcinspector1

DRP,

Thanks for the flitch plate info, put it on my favorites for reference.

Like I posted before, don't see the flitch set-ups. LVL's rule the day with engineering and install directions.

pc1


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## DRP

I just worked one typical example and picked up about 4.5" of increased span with 1/2" ply assuming that it is spliced at a point of low moment and well connected. I also assumed the ply was of a higher strength species and grade than the solid sawn lumber... when you make a composite like that the design values of the weakest member are used. In other words if the lumber was SYP and the osb was aspen it wouldn't make sense to try to increase the allowable span using aspen strength numbers, it would be better to ignore its' presence in there.

I was delighted to see lvl's, drilling a bunch of bolt holes in 1/2" steel plate and then getting it up and aligned to bore and bolt the wood was often the best part of a day, and scary with that guillotine at times. LVL's are lighter, lift em up and shoot, and then whine about how hard they are to shoot  

Another is to play with species and grade, for one the code tables are defaulting to the weakest species or group they call out in the heading. I'm playing with some beech at the moment


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## Architect1281

Ridiculous - When designing this with a 3/8 or 1/4" steel plat (Flitch Beam) You can not extend either beyond its limits

steel bending 22000 psi wood bending 1200 to 1400 psi so wood is 5-6% of steel in bending

the wood hols the steel vertical but I NEVER considered the combination as contributing to the capacity.

so OSB that is not linked or continuous or rated in bending??? adds dead load and detracts from the 2x12's capacity..............


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## Uncle Bob

I've enjoyed this thread.  I also looked into the past and found our "George's" take to be interesting as always.  I do miss him.  This was a thread in 2010 on flitch beams and ply-wood.  We are talking about osb; which I believe has no bending value.

I don't care if you put plywood between your built up beam....... [Archive] - The Building Code Forum

I've learned or relearned alot


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## fatboy

Wonder what happened to George.......


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