spiral staircase for loft

Now if I was gonna build it I would cantilever out to your length and sister it all the way back to the top plate. Then at the floating end I would go from the rafters all the way to to the floor joist. The upper section of the new studs can serve as uprights for your railing.

NOW IM NOT SAYING THIS WILL PASS CODE, just saying that's how I'd do it...

Being that it looks like that room is on the second story of your house the floor joist SHOULD be 2x6 so they are pretty strong.