A couple of questions regarding Flooring

[NorthWest1]

Hi,
I'm looking to remove uneven and creaky floorboards and lay down 22mm backer board to tile an upstairs room. I have two issues,

1. The room has an old solid fuel fire with a concrete hearth ( shown in pics ). I removed the top screed of concrete and what is underneath is hardcore, I haven't broken that up yet as I'm unsure what exactly I'll find under it, does anyone know how these old hearths were fitted in upstairs rooms ? Would I be better off trying to level the concrete with the top of the joist and fix the tile backer board to the concrete ?


2. My joists run from front to back of house and the floorboards run across them. The boards are one piece spanning the house and go under the the stud partition between the two upstairs rooms, I assume the stud wall is nailed into the board and the joist. If I cut all the floor boards at the stud wall and leave the wall sitting on the remains, I'll obviously need a support for the backer plate, where it runs alongside the joist. Is it just a matter of fixing a piece of 3x2 along the side of the joist ( to lay edge of backer board on ) or is there anything on the market that I can buy, some sort of bracket ?


Thanks

 

[noseall]

does anyone know how these old hearths were fitted in upstairs rooms

The will have formed a timber tray, to sit the concrete into.