Advise on Bathroom renovation

[MrA]

Going to be gutting a 100 year old bathroom approximately 3m x 2.5m. Walls are stud frame with lath and plaster. Room has one external facing wall with large window 2m vertical x 1m.

Planning making a walk in shower in the corner so there will be high moisture in that area. Also electric under floor heating with tiles on top. Rest of the room will be tiled midway then painted/wallpapered (bathroom suitable)If anyone has any tips on best way to do this it would be appreciated, my thoughts are bellow so feel free to shoot me down and correct...

Remove all lath and plaster from walls, leaving roof to later batten insulate and then put plaster board over.
Pull up old tongue and groove flooring (very poor state)
Do all plumbing and wiring for toilet sink shower lights etc.
Lay 18mm WBP plywood to floor joists. Joists approx 400mm spacing.
Wool insulate all internal stud walls and board over with a moisture resistant plasterboard.
On outer facing wall, leave air gap and insulate with kingspan or similar foam insulation panels between studs. Again Plasterboard over with moisture resistant plasterboard.
Tape and skim all joints, screw heads will be driven in and filled.

Fit wet room floor tray in corner and plumb in drain.
Lay 6mm underfloor heating insulation board to floor and fix using tile adhesive to plywood?
Using a paint on tanking kit apply to shower corner area sealing all joints, taping corners and gaps.
Lay underfloor heating.
Tile over underfloor heating
Tile shower area and walls.
Decorate rest of room as required install fixtures etc.

Questions...

Is moisture resistant plasterboard best way to go? Is this overkill for the whole room? Does normal plasterboard do the trick?

Any other options for insulating external stud wall avoiding condensation? External wall is solid stone.

There will be one single glass shower panel to keep most of the shower spray in the shower area but potential for water to hit floor in front hence the tanking required in surrounding area.

Does whole floor need tanking?

Does whole floor need to slightly slope to drain or will the wet room shower tray 1m x 1m be sufficient? How do you slope floor or tiles to drain if it isn't?

Hopefully some DIY expert or even a experienced person can give me some pointers before I learn the hard way

Thanks to any comments and sorry for the long winded post!

[BetterTogether]

For the most part I'm unaware of the technical stuff, I'm quite happy accepting my technical limitations and paying a good tradesman,but I have had a walk in shower fitted in a bathroom with glass panel and for the greater part I found that very little water ended up on the floor and by placing a floor mat just outside the panel dealt with the small amount that did escape. I also used tiles floor to ceiling thus avoiding the problems you get with painted walls or wallpaper .Good luck with your project and maybe put a good extractor unit in to deal with the extra moisture content in a bathroom, one thing I have noticed on many properties I've looked at up here is lack of extractor fans in bathrooms, an awful lot of them had mould in the bathroom.

[pat]

When fitting bathroom extractor why not fit a humidistat to it so fan runs until moisture level is whatever it is set then switches off and extractor shuts down.
Do not know about much else sorry - leave it to the folk who know.

[PantsMAN]

Consider using flooring vinyl on the walls at the shower. I recently did this. Totally waterproof, looks great, huge choice and no grout to bother with.

[smithp]

The shower tray will have it's own fall built in, so you lay it level.

Use ecotherm on all wall, it's far more efficient and on that size won't kill you on price, try and keep it from direct contact with wiring though.

Most people would only use the moisture resistant plasterboard in the area with direct contact to water.

[Angel]

Biggest problem with fan extractors is the venting...if you are venting outside you will get a constant draft in you bathroom so you will need a fan that closes up...also there is a noise factor to consider too...anybody who has had a louvered shutter grill fitted will know the louvers last approximately 1 minute in the wind....of those that last longer they will rattle forever...so use a fan that seals a mouse proof venting tube and fixed louvered grilled external vent...

Angel...

[Rheghead]

I've also ripped out the old plaster board and the floor boards to my 120 year old stone house. Same thing as you MrA. I will be putting a damp proof course and underfloor heating to the ground floor. Tanking up to about a metre. Stud wall insulation to all exterior walls with about 30mm air gap. I don't think water proof plasterboard is all that crucial. I'll probably put in a shower unit so I do not have to think of tiles and grout. Good luck.