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I would really appreciate some help with determining the size of beam needed for a new project and would prefer to keep a lumber yard out of it for now as they'll almost always price you up.

I can't seem to dial in these load beam calculators and don't want to assume that I have it right. I currently have 2 2x8 pine ready for the project as this is what was referred by a contractor friend. Might anyone be able to help me determine the size of the beam(s) needed for this space?

  • The beam would need to span 11' 3"
  • This is an interior wall that divided two rooms, opened up to make one big room
  • Lead bearing wall with joists spliced above where the beam would be placed
  • Center bearing roof with no trusses
  • This is on the second level, attic with storage, roof and 20-25psf snow load
  • Will 2 2x8 pine suffice, or 3 ply 2x8, or an even larger dimension?

Thank you in advance!

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  • 5
    I’m voting to close this question because this needs a structural engineer to assess the situation and sign off on the design. No strangers on the internet, no matter how knowledgable or well intentioned can safely assess this.
    – FreeMan
    Commented Nov 6, 2020 at 20:05
  • 1
    You won't be able to get a permit without proper design documents anyway.
    – jwh20
    Commented Nov 6, 2020 at 20:14
  • You either know what you are doing, learn what you are doing, or forge ahead and find out what breaks. diy.stackexchange.com/a/200474/18078 but figuring out what the lead-bearing wall above loads onto the beam are is on you...
    – Ecnerwal
    Commented Nov 6, 2020 at 20:31
  • 3
    Why close the question? The op gave all the required information: size of proposed beam, span, species of wood, loading. Just because you don’t have a structural background doesn’t mean someone can’t help the op. (I don’t have an electrical background, so maybe I should vote to close all electrical questions.)
    – Lee Sam
    Commented Nov 6, 2020 at 20:35
  • I agree with @Lee Sam. I've seen information on load beam calculators on this site before, some instructions on how to use them and then a few answers with the disclaimers, of course.
    – JACK
    Commented Nov 6, 2020 at 21:47

1 Answer 1

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You’ve given most of the required information in order to size the beam. I’ll assume some dimensions and you tell me if I’m wrong.

This beam is on the second floor and only supports the roof. The roof load is comprised of Live Loads (snow load and attic storage load) plus Dead Loads (joists plus ceiling finish, plus insulation plus light fixtures, etc.)

You have indicated the snow load is about 20-25 lbs. per square foot (psf). I’ll use 25 psf. You didn’t give the span of the roof joists that rest on this wall, but I’ll estimate 12’ each side. Therefore, if half the span rests on the outside walls, then the remainder rests on the wall. So, 6’ on one side + 6’ on other side of beam = 12’. Then multiply by 25 psf snow load = 300 lbs. per linear foot (plf) snow load on beam.

The required Live Load is 10 psf in attic. So, 10psf x 12’ = 120 plf live load on beam.

You also indicated that the roof structure rests on this wall and it’s not a truss. The Dead Load of roof framing AND ceiling framing is about 20 psf. Therefore, 20 psf x 12’ = 240 plf on the beam.

So, the Total load is 300 plf + 120 plf + 240 plf = 660 plf on beam (assuming the roof joists and ceiling joists span about 12’ each side on the beam).

So, in order to span about 11’-3”, you’ll need 6-2x8’s or 3-2x10’s or 2-2x12’s. All are pine (per your direction) with a grade of No.1 or better.

If you use Doug. Fir, then you can reduce it to 5-2x8’s with a grade of No.2 and better.

Use two trimmers at each end and make sure there’s a support (something that equals 2 trimmers) under each end all the way down to the footing.

Sizing the footing is another issue. You’ll need to make that a separate question.

If the wall does not have plywood on it to connect the beam to the trimmers, I’d use a metal post cap connector like Simpson ACE series and a metal post base connector.

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  • This is a question out of a Statics course and has been answered. I'm not sure what all the fuss is about.+1
    – JACK
    Commented Nov 7, 2020 at 12:23
  • Does this meet the permit standards?
    – Solar Mike
    Commented Nov 7, 2020 at 13:15
  • This is, I'm sure, a correct answer, but it doesn't constitute a Structural Engineer's stamp/signature that the OP probably needs to get permits approved and, worst case scenario, an insurance claim paid. I have no doubt about your good intentions or the accuracy of your work, I'm only concerned that people may skirt the rules because humans, being human, will often try to do that.
    – FreeMan
    Commented Nov 7, 2020 at 15:40
  • These are fairly straightforward calculations. Nothing complicated, no complex joints. I think the local jurisdiction would approve something like this provided the homeowner put together a sketch and showed his load calculations. This is really not much different than a deck, which gets permitted and built without a structural engineer's analysis, a least in most cases.
    – SteveSh
    Commented Nov 7, 2020 at 16:02
  • Thank you all for contributing to this thread.
    – jcarpenter
    Commented Nov 8, 2020 at 15:08

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