floor heights: Screed and fibre cement sheeting ? both?

i'm very new to all of renovations and this forum, so please go easy on me. i've been trying to understand the various options & costs - in terms of trying to level my floors so we can tile and lay carpet on them.

The unit has a concrete base and i've been told i can either screed or put FC sheeting.
I've been told the screed must be at least 35mm high, however reading other posts as i may only be using 300x300 or 400x400 tiles - the screed could possibly be lower? Can any experts out there verify?

For the kitchen (& living)
- Do i necessarily need to screed this area or is fibre cement sheeting enough? Which is more cost effective? (Strata rules require to install an acoustic underlay for hallway - i dont want to raise the base floor height unless abosolutely necessary)
- Additionally, as this room, it flows into the living area + bedrooms so i will need to raise the floor to somewhat match the kitchen. I've read on an earlier post an option may be lay down ply wood. I understand there is thicker carpet underlay but that would potentially add to +$10/m2.
- I've even read it may be possible to even glue them directly onto the concrete base? Is this recommended?

For the bathroom:
- I have been told i would need to lay compressed fibre cement sheeting down, however reading posts here it talks about screeding to allow tilers to create the 'fall' of water to the drains. Do you need to put both? Or isn't creating the screed enough? What would be the purpose of the fibre cement sheeting if you had the screed?
- What could be the potential minimum height of the bathroom floor if we wanted to keep it down?
- 20mm for screed <-- is this possible or even lower?
- 2mm for waterproof
- 10mm for tiles & adhesive
ie. min of 32mm.
At the end of the day, i am hoping where the carpet meets the tile, there wouldn't be a noticable 'step'.
Other Posts Here Here there could be a step of 57mm!!!

thanks
Jim

If you are on concrete there is no need to lay any sheet flooring at all. The tiles woould be laid straight on a bed on the concrete. The bathroom floor would need to be water-proofed and a screed would be needed to allow water to run into the waste hole

Hello,

I was reading your email regarding screed and fibro:

I am presently about to tile a WC (toilet) floor and we have had to place fibro over the original timber floor as it had many many years of old cement and multi layers of tiles built up on it. Subsequently it is about 3mm out slopping to one original corner which must have had an old drain which was no longer there when the floor was pulled up.

Will I need to screed over the fibro to level this minute level or can I just tile and build up the tile glue a little more in that corner?
If I screed then it will be very thin on the level upper corner/side and I am thinking it does not need to be, but seeking advic eon this.

Cheers!

Lynette