Re: replacing header mechanics
Well, an open-ended question.
Is this an exterior wall?
Analyze what loads are there. If there is a floor load above, you can support that with a temporary stud wall below in the room, a workable distance back, like 30" maybe. Then the roof load can be supported by bolting a 2x12 into the studs above on the outside, to tie all the studs together. With a few extra bearing blocks under the 2x12 into the not-to-be-disturbed studs at the ends, also secured with bolts (large Spax or Headlock screws are great for these fastening tasks) You would have the freedom to enlarge the opening.
If you have a stick-framed one story (not roof trusses) you can support the ceiling joists with a light 2x4 wall, and have the needed working space inside, and after removing the soffit you could get an idea how to work in the temporary 2x12 to support the rafters using some of the above ideas, just don't screw into the old header. But you can probably screw into the plates, and catch some undisturbed studs.
If the header is supporting trusses, it would be a bit stickier, because there's probably not as much room for the 2x12 on the outside, but w/o a second floor, the loading is much less, just a ceiling and some roof load. The temporary wall will be all you can get, and it would have to be right against the outside wall, (trusses lack enough strength to support themselves, generally, anywhere but at the plate line) and without the freedom of access, you would need to work entirely from the outside, taking out a lot more siding.
If it's an interior wall, and the joists run through, put the temp. wall on the side of greater load, or temp wall both sides of the opening.
So, that's the way I see it. Don't take any risks you're not comfortable with.
Last edited by Sombreuil_mongrel; 07-31-2011 at 10:41 AM.
Reason: add'l text
Remove not the ancient landmark, which your fathers have set.