What are the requirements for a header for an open passageway through two rooms?
The answer to that question is project specific. Some general advice below, but the project specific requirements depend on local regulations as well as the structural requirements of the design itself.
Obligatory: hire an engineering firm to investigate and "be sure" (in quotes because engineers can be wrong, and really what we hire an engineer for is in large part to take on liability for problems caused by proceeding with the work).
That said: yes, you should be able to delete the intermediate headers ("drop headers") on interior partition walls in single family, wood framed, residential construction in the USA without impacting the structural integrity of your home in both your first and second cases. Generally speaking, you'll want to selectively demolish layer by layer and make sure you reconfigure any structural "Load Bearing" elements appropriately. What I mean is, if you pull the gyp board off and find that the wall is sheathed with a tight nailing pattern and is clearly "built up" (more than just 2x4s and gyp board) beneath the gyp board, then you should assume you have a shear wall. Otherwise, as far as single family typical residential construction in the USA goes, any structural elements in a wall with an opening (like the doorway) should be directly beneath the Load (in this case, at the top of the wall (note: where no cracking or other defects are visible which might imply that the opening was cut into a structural wall as a renovation and compromised the integrity of the "work" the wall is performing). In your case, I don't know of any reason why a structural header would be built above a doorway with a pony wall above it supporting the actual load.
To address your first scenario in specific terms, the picture shown above: If the information above applies and is accurate, and we determine it is reasonable to proceed assuming this is not a shear wall, you have two options in the event this is carrying a joist running perpendicular to a Structural Header at the ceiling plane above the doorway header:
- Demolish the wall up to the header at the top of the wall.
- Learn some framing tricks, strap the load to an adequate (including appropriate safety factor) beam riding above the joist thereby transfering the load, and delete the wall all the way to the ceiling plane.
To address your second scenario in specific terms (the T intersection):
- Same as above, if you go into your attic, and you don't see any bracing from the roof to the ceiling joists riding on the plate above the openings, and if everything else above has been followed and you determine to proceed accordingly, the only problem impact you might find is cracking from settling.
- As a general rule, leave the upper most header. That is, if you remove the finishes and find that framing is riding on an intermediate header, and if you are worried about leaving the top plate unsupported by demolishing that header and if it is not feasible to transfer the potential load from below to above the element itself, then you would install temporary posts on each side of the work and to be extra safe you would put temp posts directly below at each level of your home down to the foundation (which may take selective demolish of the ceiling finishes to brace to the underside of the subfloor above), and then you would delete the existing wall and reuse or replace a header of the same design directly beneath the top plate with new bearing elements of the same design as previously removed.
To address the framing element requirements (header, king, jack): there are three scenarios:
- If the wall is structural; this depends on the load, and you have not provided the information I would need to offer a layman's safety factor answer.
- If the wall is an interior partition not serving any structural function, you only need the minimum sufficient material to fasten and support your finishes.
- If you are doing this work under a permit and subject to inspection and local code, or if at any time you are concerned about liability for deficiencies of the work, you will want to revise your post with the exact details of your jurisdiction, type of building, type of occupancy, building elements affected by the work, and any other technical details that come into play. First, you would consult with your jurisdiction's building department to see if they have any technical memos on the subject, then you should engage a designer as needed.
The important point I'm trying to get across is that you should only proceed if you know what you are doing and you are willing to take the risk even if you know what you are doing. Also, if you're not the owner, check with your landlord first.
Good luck @dabi!