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My engineer has designed a 6'6" beam to carry my load and this would consist of 3 LVL glued and screwed together. 7 1/2" LVL. Like most LVL, a single ply is 1 3/4" deep. So, as he has it specified 3 of those will be put together and that'll be 5 1/4" deep. However he has specified this will go inside / span the bearing wall, which is a 2x4 wall. In this case, he has also specified that each end of the beam will bear on only one 2x4. I don't doubt his design necessarily but would like more explanation on how/why it is legitimate to bear the 5 1/4" beam on a 2x4 ( 3 1/2" actual depth). I've attached a sketch below for clarity looking at the side of the 2x4

enter image description here

link to engineer doc https://drive.google.com/file/d/1vlIXbt2FQ_YYJN9PjOkHpAx7pcumKWch/view?usp=sharing

  • Agreed. About half of the outer plys would bear onto the 2x4, but about half would not. I imagine it might be legit in a case like mine where the load isn't huge and maybe not in other cases. A 2x6 would ensure full bearing but then that would sit proud from my 2x4 bearing wall. I'm just looking for the rationale. – Brian G Feb 7 at 14:03
  • FWIW those deckmate screws are supposed to have some ridiculous shear strengths, but it still has me scratching my head a bit. I'm entertaining the idea that he made a mistake, though I don't think that is the case. – Brian G Feb 7 at 14:05
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    Bearing isn't a concern. With half the outer members on the lumber it'll carry fine. My concern would be the single stud. Typically beam posts are at least doubled studs, if not tripled. Are you sure just one is spec'd? There may be notes about adding a second one. I suggest that you post part of the actual drawings so we can help interpret. You may have misunderstood something. – isherwood Feb 7 at 14:08
  • @isherwood I will see if I can upload though the drawings are in fact pretty minimal. I did a bit of research because this was also concerning to me. It sounds like doubled studs are more necessary on shorter spans AND longer spans due to the dynamic versus static load components, but honestly I didn't understand all of what I read. I'll see if I can post the engineer's docs. – Brian G Feb 7 at 14:11
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    Realized I misunderstood the beam width. Need more coffee. – UnhandledExcepSean Feb 7 at 14:16
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None of us can really answer this with confidence, not having all necessary information (or, in my case, an engineering degree). I will offer a few assumptions and suggestions based on the engineer's drawing:

  • A tripled, relatively squat beam is probably being used to maximize head clearance. More typically this would be a doubled 9-7/8" beam, which rests more comfortably on a single trimmer stud and fits within a 2x4 wall. You might consider whether that's a more desirable option than having a beam that exceeds the width of the current wall.
  • A single trimmer stud is apparently adequate for the load on the beam (though it wouldn't hurt to ask the engineer rather than us), and the attached full-height (king) stud provides the stiffness that I was concerned about in my comment above.
  • On second thought, this looks like a "flush beam" situation, whereby the beam is at and above ceiling line. Concerns about beam width in relation to wall width are probably moot, and the beam will rest on doubled studs per spec.
  • Otherwise, you could always double the trimmer studs to alleviate concern. This is a low-cost solution that may bring peace of mind.
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  • I know that the first bullet is a fact. We discussed this, since we want to "tuck" the beam into the ceiling and have the drywall be flush. – Brian G Feb 7 at 14:45
  • I just figured that out and updated. Thanks. – isherwood Feb 7 at 14:46
  • As to the second bullet, 1 stud under the beam (the jack stud), and the king stud you're referencing is a stud running from the bottom plate to the top plate/ tie plate of the existing bearing wall, but is flush up against the beam's jack stud. Is that correct? As to the third bullet, I agree. – Brian G Feb 7 at 14:49
  • As to the fourth bullet, are you referring to the jack studs that are actually bearing under the beam? I have cut the LVL to 7 feet for the 6'6" opening so that I could possibly add an additional jack stud, since I had the same concern. I may not have to space for it on one side, due to the beam running up against the stairwell, but I can try to make it fit. – Brian G Feb 7 at 14:49
  • I am trying to keep up with the edits. Can you clarify "the beam will rest on doubled studs per spec." I may have misinterpreted the engineer doc. – Brian G Feb 7 at 14:50
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Trimmers are designed to support the total load without crushing the fibers in the wood beam where it rests on the trimmer or from crushing the trimmer.

The engineer notes in the letter that the new beam is to support the second floor (one floor). There are no dimensions given, but using 2x8 floor joists at 16” on center, They can span about 12’-9” maximum, depending on the species and grade.

So the floor load on the new beam is about:

50 psf (Live Load of 40 psf plus a Dead Load of 10 psf) x 12’-9” = 637.5 plf

So the load at each end is:

637.5 plf x 6’-6” / 2 = 2,072 lbs.

One 2x4 trimmer has an area of:

1.5 x 3.5 = 5.25 sq. Inches

Therefore the stress on the trimmer and the new beam at each end is:

2,072 lbs. / 5.25 sq. In. = 394 per sq. in.

Wood in compression parallel to grain (the trimmer) can support about 1,100 lbs. per square inch, which is significantly under stressed. However, wood in compression perpendicular to grain (the new beam) can only support about 500 lbs. per square inch, which is slightly greater than the actual 394 lbs. per square inch.

So, one trimmer is acceptable, provided: 1) the hose is not more than 25’ wide, 2) there is no roof load on the existing wall, 3) the LVL’s are Douglas Fir No. 1 or better.

The most important thing is to verify that the engineer accounted for all the loads on the new beam, INCLUDING any roof loads. I’d look in the attic and see if any ceiling joists or roof joists bear on this wall and ultimately the new beam. If so, I’d notify the engineer immediately. (As he says in his letter, he wants to know if any of the conditions are different than what he has shown.)

Btw, I’m surprised he did not stamp the drawings. It’s required in every state. (I think you’ll find out he’s a civil engineer, not a structural engineer.)

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If you're in direct contact with the engineer, I'd go back to him with

Hey, Mr. Engineer, this is pretty cool! Let me ask you something, though. From my uneducated non-engineer's perspective, this doesn't quite make sense, would you explain this to me?

i.e. acknowledge that he's the engineer, you're just Joe Citizen and ask him to talk it through with you explaining why it's OK. He may realize that he's made a mistake (if he has), or he'll explain why it's OK as is and put your mind at ease.

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