oklouise thanks for the ideas. We have actually really thought about the zoning. We want the two bedrooms on the southern side with a bathroom between for privacy. We also want the eastern lounge room to pop out as a dining room in that spot will waste a gorgeous view. We had a straight alfresco and thought it was all a bit hohum. I will attach the first and second drafts to see where we have come from. The first draft we had drawn was too boring for us ... Garry hated draft 2 as he thought it was too wide for solar access and didn't give cross ventilation (north to south or vv). It's only positive was the flow of west/east cross ventilation. Also the bathroom was too tucked away for guest use when we are using that nice alfresco area. We quickly scrapped all those ideas... LOL As I said, we like skillion roof lines and are planning on clerestory windows to maximise northern sun. Some raked ceilings will probably happen too (and definitely 9 foot ceilings in living areas). the mudroom/laundry will probably be incorporated into the hallway. Unlike some on this forum previously I don't object to entering through the laundry. It kind of gives a landing spot for groceries from the car on those cold days you don't want to leave the whole house open. The garage may actually be a carport to ensure we can have ventilation come through that way and to help us with budget.

Sorry my phone played up and posted before I was ready. I'm looking to style the new addition so it is noticeable as a new build with square set ceilings, polished concrete (easier with all the sand) and different external material but have aspects that relate back to the older building. Such as paint colour the same, window furnishing etc. The girls will most likely share a bedroom - I was thinking of using the one that was located linking to the winter deck as it was closer to us and away from the front of the house. It's not a big deal though as it is very quiet where we live (mainly holiday homes) and any bedroom will be fine. Thanks again for all your help and interest. I really appreciate it.

answering your questions: change the sliding door to a bench height sliding window and use the salvaged sliding door in the western end of the dining room where the best entry position is for the deck, you MUST have a proper legal drains do not consider anything else...the drain pipe for the garage laundry can be on top of the concrete floor, behind the washing machine and through the sink cabinet and/or under built in storage and only needs a few cms not a whole floor and no stepped up area that you would see or trip over.. the laundry can't be in a separate room as there's not enough space for a separate laundry without compromising the size of the garage...a laundry cupboard 80 cm deep is enough for the washing machine (allowing for the drainage pipe) you could use the old line cupboard to store anything you want but it's not cost effective to change, the entry foyer is already as big as in many modern homes and there's generous flatpac biw space in the small study.... the family bathroom is 2380 x 2370 (ie the old study minus 1m for hall way and wall thickness and, arranged exactly as shown to allow for the wide window there should be space for a bath up to 1800 x 750, vanity about 1200 x 500 and shower space 1200 x 800 and leftover space makes the small linen cupboard with the door deliberately opening towards the shower to use the back of the door for hanging racks for towels and clothes....btw i understood your priority was maximizing separate sleeping rooms and minimising costs...my last plan has five separate sleeping rooms plus the lounge with sofa bed totalling sleeping places for at least 10 people plus the potential for bunks in the garage so you need to decide what is most important and where you're prepared to compromise

also in NSW we were given permission to build a habitable room over sewer pipes as long as the the sewer pipes were encased in concrete according to Council specs and we couldn't use a concrete slab floor and had to build the room on piers with an accessible crawl space underneath the floor..we took all our info to the local building inspector and they suggested an ideal work around (by moving our building sideways) ..but i'm shocked that your building designer allowed the planning to progress this far without identifying the potential problem ..could you move the studio closer to the house with a courtyard space between dining and studio or build a proper non habitable room ie out of different materials eg a sound insulated steel shed build on piers..there must be an answer and your building designer needs to do the research as they should have already known..best of luck