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I'm looking to run some electrical & CAT5 in my place as well as potentially some larger projects such as removing some partition walls. As a precursor to this I decided to model my house in Sketchup to get a better idea where things are and what's structural vs not.

I'm stuck on trying to figure out how the stairs are framed and what's supporting them at the split in my side-split. I've attached a few views of my plans so far. There are two sets from the ground floor to the 1st floor (red), and one from the 1st floor to the upstairs (purple).

I was hoping someone could help me figure out how the floor joists might be laid out on the 2nd floor. I've been able to determine the direction of them as indicated by the green and blue lines.

I've also put my best guess at what it might be at the bottom. Perhaps someone could comment on whether or not this is realistic.

Front View

Top View

Isometric

Photo

Proposed

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Wow, you even opened up some of the wall to help determine which way the floor joists are running. (Often this is done with a “stud finder”.)

I see nothing unreasonable about your joist layout: 1) joists follow what you discovered when you opened up the wall, 2) joists span the short distance across a rooms, 3) joists have “normal” span lengths, (nothing excessive)

However, I’d guess the joists were doubled where joists change direction.

To answer your question about how stairs are framed, I’d go to Architectural Graphic Standards. (You can Google it.) Typically, 2x12’s are notched for the proper “rise” and “run” called stringers. I’d guess there are 3 stringers: 1 on each side of each stairway and 1 in the center.

  • I actually opened the walls up to run electrical to the attic, but obviously didn't pick a great spot to do it in hindsight :) The one thing I'm really not sure about is the short wall on the right side of the central stairs. It seems like this is supporting the two horizontal joists that land on it, however there is nothing underneath for it to bear on, just the lower level's floor. Does that makes sense? I'll check out the Architectural Standards! – Otus Dec 12 '18 at 21:19
  • Yes, the wall could be a partial height wall and the floor joists could frame into a beam designed to carry the additional load. The joists would be connected to the beam with “joist hangers” similar to this: homedepot.com/b/… – Lee Sam Dec 12 '18 at 21:59

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