If you "change" anything that involves a building approval then the floor area on the plans relevant will count towards the overall amount. If it amounts to beyond 50% of the existing conditions then the whole building becomes applicable to energy calculations and so you enter into up spec'ing existing areas. And yes it can often be a good thing to be doing anyway, but of course it costs money. If the total area being changes is below 50% then only the areas of new work are applicable. I'm honestly not a specialist in this area, but I have to deal with the issues naturally in the course of the design and resolution of project solutions I provide, and hence I use an energy consultant regularly and we have a way/system of working through together how best to achieve the requirements for permit. As far as I understand it's a case by case/project specific exercise and also there's various ways of negotiating/achieving the necessary performance requirements - e.g. you can play around with different levels of insulation together with a particular glazing/window spec, and depending upon circumstances you can save money one way or another. Sometimes I'll squeeze windows overall down to get it under a certain amount to not trigger requirement for expensive glass...also timber windows rate better, but if you are in a bushfire area you'll be caught out or require very expensive timber windows...it's a real juggling act in particular contexts...which is why you really need to be working collaboratively with an energy consultant/specialist to work out the best solution in this regard, as well as the other aspects of design, structure and bushfire etc. It's a true team effort ;) If you're really up for some technical reading you there is some further energy info here NCC Volume One Energy Efficiency Provisions 2016 - Australian ... but it may get confusing........Coming back to the core of it, my advice: 1. define your budget 2. list and prioritise your requirements 3. seek some preliminary advice/assistance from a seasoned designer doing this type of work to test whether or not the general concept of what your endeavouring to achieve is viable, and this depends upon the relevant context/existing conditions etc (and bushfire rating is yet another layer on top of all this), and then refine the concept from there. If you are just doing a bathroom or kitchen isolated then you can arguably do it yourself, but if you're re-jigging the whole house like it appears you are heading towards, and on a very tight budget then I'd highly recommend (to save yourself headaches and frustration going around in never-ending circles) to invest some of your available budget into front-end design, to get to a solution that works to your nominated priorities so you achieve a viable and professionally advised outcome. Trust me it will be money well spent. Have a great Christmas, and best of luck with continuing to work through it all :)

Thanks everyone - your comments and diagrams have given me plenty of ideas I hadn't considered. Perhaps shifting the wall is a little drastic! I'm now thinking of going a long U shape like this. I'll add a few upper cabinets on the left side too for the most frequently used stuff from the pantry (as the pantry is still a distance from the stove/oven). The fridge as you can see is now right amongst the action. We also have a chest freezer hiding out in the laundry which I can move into the old fridge space...alternatively I might convert it to a computer workstation as suggested. I'm leaning towards a peninsula rather than an island, just because I feel like it will give me a slightly more efficient/seamless work space, and we don't expect seating at at the island/peninsula will get used much given how close the dining table is. Any thoughts on this revised layout?

You are most welcome, I have always said that I haven't been put on this earth to "Hug" toilets, so I'am wondering who is going to clean all of these Bathrooms. Our two kids a boy and a girl had the upstairs "apartment" which they and all their friends loved. I have added a timber stair case for fun, there's plenty of space but you will need to decide what you want to do in the attic and place the stairs to open up into a tall space. I have also turned one of the ensuites into a powder room. Your Jacaranda's only drop once a year!, you used to be able to trim them by 25% each year, you would need to check with your council, we were on the lower North Shore, I think you should consider the patio side of the house and make better use of that, is the front deck something you plan on adding because of aspect, and plant some tall growing hedge ready for the apartments. Our kids Attic desk/study space over looked our pool in the rear garden. With respect to using the formal rooms for bedrooms, you will find that once you have your large family/alfresco and the kids have their upstairs space if you still feel you need it, it would make a great office. You spend most of the time there only using only using the front room in the evening for watching movies etc. I have had another play with my floor plan, I think if your wife sees this you may be in trouble, it's a Master Suite, the free standing bath in the window alcove with white timber shutters for sun and privacy control..... Iam' adding a couple of photos of our old Federation which wasn't protected, when we sold it the new owners removed all of the Fret work & posts replacing them with simple timber posts. The front rooms which we didn't use very much once we opened up the rear rooms into a family area. The room with the Bay window had a Baby grand sitting there, we sold the piano before we took the photo. Cheers

Not sure I'd be in a hurry to create a home where you open the front door onto a dining table and chairs. I'd say it's very likely that that little partitiion wall is holding up the roofspan and it may be costly to remove. If you look at the floorplan you can see the walls run vertical right through the centre of the house. I wonder what is not working about this layout? Even with the wall removed you will still have to turn left or right when you enter the house anyway. Just removing storage won't change that. I would be more inclined to remove the ugly storage and replace it with something more attractive that works for you in the space. Like a cloak and shoes closet or similar. Turn that entry into an attractive mudroom. Then it is no longer just wasted space with annoying blank walls near the door. But a proper entry with a useful purpose. Then the irritation of it will go away. People are always quick to decide they need to remove walls in a home when in fact that may not be the real problem at all.