Need opinions about new balcony framing

[shacked]

I posted something yesterday related to this topic, but I had not yet fully thought through all the issues.

Here is what is going on
Existing conditions:
2 story wood framed house with 2x12 fj that cantilever out 3ft and support the wall/roof load from above.

Proposed condition:
New balcony in front of the wall above. Loading from above is also changing(increasing) due to changes in the bearing walls above.

Question.
How would you support this new balcony?
Initially I had thought about adding a steel beam under the wall above. The steel bm would be supported at each end by new steel beams cantilevering out, then sistering 2x dj to the existing fj. The new dj would have an 8ft backspan and cantilever off the new steel beam as the new balcony. Im using steel because the 18'-6" span and a wood bm would be too deep.

Just would like to get a few other opinions on this. I think there may be a better way to support the new balcony, and I do believe that by cantilevering new DJ out may create a waterproofing problem.
Thanks

 

[lexpatrie]

Can we get a Captain Crunch decoder ring for half these acronyms? What's a 2x dj?

This conceptual detail does not look like it will calculate out, unless I'm missing something.

Does this framing scheme work as-is for the original loads or the changed loads?

 

[DoubleStud]

I personally would put a steel beam under that very end existing wall. Then I would put 2 beams or more of steel beams cantilevering out (2:1 min. back span). This way the main structural supports will not rot. Then you frame the balcony joist north south hanging from steel beam to steel beam. I think you want to avoid sistering 2x deck member to existing joists because it will be very hard to replace when it rots.

 

[shacked]

Sorry lexpatrie, I love acronyms. 2x deck joist....Dj, Floor joist Fj..

Dblstud, this is one of the other methods that I had thought about as well. Good point about sistering deck joists and "when they rot" is correct, because they most likely will.

Another question has come up about cantilevering a wood beam(psl), or steel. The beam would be supported at the garage wall and the steel beam running vertical on the drawing. Since these supports are closely spaced there will be uplift at the garage wall support. Would it be a good idea to design the beam assuming only a single support on the steel beam and neglect the support at the garage wall?

Thanks guys

 

[lexpatrie]

Ok, I kind of see it now, you're intending to sister a double joist to the face of the existing 2x12 (full sawn?), with an 8' overlap and a 4' cantilever. That sounds potentially viable.

I'd want to model the work as closely as you can to the actual condition, rather than trying to "simplify" the design load and perhaps miss something, there should be a vertical reaction at the 8' end, if you're going to address that as a "point support"? the load may potentially come out as more distributed into the fasteners, but that simplification feels justifiably conservative, but that upward load would be 5' from the wall, based on the drawing, so determine the reaction and attach as needed to the wall for the gravity uplift.

 

[JoshPlumSE]

I personally would put a steel beam under that very end existing wall.

I believe that's what the OP is proposing.

I worked on a project that was reasonably similar. No wall above and we were merely converting a very modest deck into a much longer, extended deck. IIRC, we uncovered the floor joists in the back span and sister-ed new joists to support the longer deck. I tend to think that the same thing would work here.... you'd be sister-ing the joists before adding any new load (meaning you'd have shoring to support them). Additionally, you'd add the steel beam underneath with whatever new posts support it. Not sure what the contractor would want to do first.