Hi,
I've gotten to removing the last part of the existing floor, the section from front door to under the stairs ( the bit thats under the first couple of steps, boxed in with lath and plaster ). This is difficult to access, though, I have cut out a section of the closed understair in the living room. The stringer thats opposite the wall doesn't come and rest on the concrete floor, which surprised me, instead it looks nailed to the vertical stud that forms the vestibule and runs ( I presume ) to the first floor and the loft to form the studding for the plastered walls. This stud ( 3x2) bears on an block of wood and looks to take the weight of the stairs.The wall side stringer comes right to the floor and bears on a block of wood.
Would it be a problem if I treated this area independantly, its about 20 bags of 20kg concrete ( 1.5, x 1.5 m ), I would give it its own piece of insulation and DPM. It would make it easier to work on and get the stairs supported before the main pour for the rest of the house. I wasn't sure if trying to tie a small area of concrete into the main slab would be an issue ?