I have a header question. I am moving a load bearing wall and need to span 7’4″. The span supports a second floor living space, 26′ wide, but not the roof (the roof is clear spanned to the masonry sides of the building above the second floor). The 2012 Code tables, as I read them, (R502.5(2) specifically) call for a 3x 2×10 header with 2 jacks.
My question is a 3 ply 2×10 beam will not fully bear on 2 jacks. Can I substitute 2x 2×12’s instead of 3x 2×10’s? Should I switch to an LVL? If so, what size?
Thanks!
Replies
This is a structural engineering question that won't cost you very much to engage said engineer
Use a couple of 12"LVLs.
Disregard the guy saying you should spend money on an engineer. The LVLs will cost $100 and you will be done in 2 hours.
Using nominal dimensions the Moment of Inertia (also known as the Second Moment of Area) is 576 inches to the 4th for the 2x(2x12), and 500 inches to the 4th for the 3x(2x10). Therefore the 2x(2x12's) will be stiffer.
If shear is a concern, which I don't think it is, but I'm not a structural engineer, then the 3x 2x10s will have a 25% higher shear strength (again using nominal dimensions).
Sorry I didn't make clear that real lumber yards, not box stores, have access to engineering services. Most professional builders/contractors are aware of that.
I'm not sure I understand your comment about needing long 2x12's. He is only spanning a 7'-4" opening.
My comment was with respect to the code, in it's generality, not the specific span. I have no experience with the code. Are 2x12s a generally stocked item at lumber yards? I have no idea, but doubt they are, given my experience with P.T. lumber when buitding steps to the deck. The maximum length was exactly what I needed, 7 feet and I remember thinking that it is a good thing the deck isn't higher off the ground. My only reason for commenting originally was to freely provide the engineering info needed to use regular 2x12 lumber in the application.
If I understand your question, two 2x10s would be adequate. Based on a 40#/sf L & D load, you are only supporting +/-3800 lbs.
You must be looking at the span tables wrong. But don't believe me.
Go to your local "real lumber yard". They should be able to advise you.
Just wanted to add that I am a mechanical engineer, just not a structural engineer. You can rely on my calculations. It's simple first or second year strength of materials. No charge for the consultation. The code might have stipulated 2x10s because long 2x12s are not readily available. I know that I was pretty limited when I built the stairs for my deck. With respect to 2x12 LVL beams (and other man-made beams, like glulam), I don't know how the stiffness or strength compare to "real wood" of various species without reviewing tech notes or data sheets from the manufacturer. That info is readily available though and I'll leave that for you. Contrary to oops' suggestion, I wouldn't trust any information that I receive at any lumberyard.
I have to disagree about not trusting information from the lumberyard. Most yards that sell engineered lumber have access to that supplier's engineers. They'll spec beams using their material, usually at no charge.
I apprecitiate the clarification that you brought to my comment. IF the lumberyard contacts the supplier's engineers, and that needed to be clarified, then the lumberyard is essentially acting as a middle man for the info.--which is good.
Go to the lumber yard or big box store is fine as well. They will talk to engineered lumber supplier directly to determine size of beam with the suppliers in house engineers. I’ve sat in multiple calls with my sales rep talking directly to Weyerhaeuser (the company that produces a lot of our engineered lumber). You provide them the specs of the beam you need over the phone or email and they’ll tell you what you need. If it’s a complicated situation they may request a blue print to decide. I’ve also gone directly to Weyerhaeuser multiple times. There are 3 locations w/in a one hour drive from where I work. Weyerhaeuser is a huge company, I’m sure there is one right around the corner from you.