It's not a simple debate between what you want/need more or less....understand that this a regulatory thing.........if you are dealing with a building permit then it's pretty cut & dry - as the BCA reads, a separate trough is technically required to consitute a laundry....happy to be corrected in my interpretation in this regard but we have had to deal with this exact issue on a few occasions....... But if you are doing just an under the radar laundry reno/refit (no permit) then potentially you can get away with none, but you'll of course need to practically connect the washer into the drainage somehow, which still requires an isolated trap set-up, that technically will be illegal. No you can't just connect straight into a sewer waste as if the connection fails and their is no water trap it would be hazardous (not to mention unpleasant) to have exposed sewer gas. If it's in a kitchen an can connect a washer to a sink waste (similar) to the dishwasher) then arguably that could be passed. The easiest way is to fit a small trough next to the washer that even if you develop a cover for so you can use the area as bench space. It then keeps flexibility and everything above board/compliant for future resale.....

my suggestions would be to leave the toilet, bath and vanity in the existing locations, move the bathroom door and install the new shower in that corner...this means reducing the wardrobe to add a new bathroom door but an extra wardrobe would add more storage in the bedroom ..the new shower and door would have to smaller than ideal but still within standard sizes available and a hinged door could have a towel rail attached and is better for moisture control and it might be possible to recycle the existing door and architraves

To answer dreamers question as to why you might do this, I turn on my shower over my bath with the kids in there and put the plug in. The shower water fills the bath and when there is some depth, I turn the shower off and they sit down. I supervise the whole time, blowing bubbles and playing with them and they love it. I also keep a small stylish stool beside the bath so I don't have to sit on the ground. My children are 2 and 4. Obviously if your children are older this would not resonate :)

Hi oklouise The sad part is the existing bathroom is beautifully finished! This whole house was well finished and really well built. It was sad to have to demolish things that were so well done, but the design problems made changes necessary. The bathroom has porcelain wall tiles floor to ceiling on all walls and a white polished porcelain floor (slippery as all hell, and a mongrel to keep the grout lines clean!) is laid over a full 300mm+ of solid concrete, under which are all the drains. Outer walls are 200mm of reinforced solid concrete. Tiles on internal walls are over cypress timber frame with generally two layers of lining glued, screwed and nailed on - and there is way more timber in the frame than necessary. I think the builder (who built it for himself) thought the house would last forever and would never need to be changed in any way. Exact distance from external door to wall is 1.1m on both vanity and shower side. The door combination is 1200 wide and placed dead center. It's worth noting that 300m on the vanity side of the door is full-length frosted glass panel and it's possible to infringe a bit on that area if absolutely necessary, provided there's enough room for the door to swing safely (as it swings toward the vanity. I will take some photos now and share.