You are proposing to delete and add lots of plumbing. What is your floor, concrete or timber with crawl space?

Good point, timber with crawl space in the current bath and bed 3, I believe concrete in the 70s extension ie current living/laundry etc areas

Stage B doesn’t seem improve orientation anymore that the current layout. Except for having the second living at the front of the house. Is that the only goal because there are cheaper ways of doing it?

Idea B gives us a master with ensuite keeping plumbing in same location, but would need a roofline change to add clerestory windows above the internal living/dining for light. In reality I think we’re looking at needing to change the roof either way. It may be cheaper/easier to KDRB the extension or whole lot so we’ll consider that too (this is all long term), but hoping to be a bit more sustainable in our approach and retain the the embodied energy and materials of the outer shell at least.

Anytime you’re looking at changing the roofline of an older property particularly one with an extension of will almost always be cheaper and easier to KDRB. I like your intentions of a sustainable approach but it will be difficult to get a builder that will take on the more difficult approach. I’d place a bet that it would be cheaper to move plumber than change the roofline to the extent you’re considering. After you’ve gotten some layout ideas from the plan people here on Houzz it would be worth paying a builder to give you a ballpark figure for your ideas before you go too far down the planning path.

Your porch between garage and lounge appears covered. I would change that and part of garagecroof to translucent panels and make the door into lounge a bigger glass entry to get in northern light Skylight where you can . The rear verandah roof along should be all translucent. Cost can be so variable.

What a lot of external buildings, what are they used for or could you demolish them from the garage back.. The current rear verandah roof replaced with a Vergola style roof so it can be opened and closed in sections

Raising the extension roof to let in light would need to be done at start so difficult to stage as you will need new windows and will want them in the right location. I think you need to consult directly with an architect who can come and look at your block, existing features and standard to get detailed advice. They can advise on local costs but be prepared for costs this won’t be cheap/

@oklouise thanks for your suggestions, I really like the mudroom/pantry configuration and think that could work well. We are really hoping to have a bath in the shorter term for kids, is there a way to fit that into your suggested ensuite? However term I do prefer a bath in the main bathroom.

@siriuskey a lot of covered area indeed!! The garage is covered all the way along to an undercover alfresco, but the main covered space at rear of the property of a double brick granny flat. Will remove the shed in middle of the garden and probably some of the covered alfresco too.

You mentioned having just replaced the flat roof so would work with that and changing the verandah across the back to a flat roof Vergola style which along with removing some of the buildings/roofs behind the garage will allow for a lot of light back into the house, Vergola can also be used on large skylights to manage cold and heat plus look good.

new ensuite with bathtub ...connecting door to master bed can be added and old hall door can be closed off as needed when you have the extra bathroom

and, as there are steps up to the old living areas from the side and rear verandahs i would be surprised if the whole extension has a full concrete slab and a crawl space under the old lounge would make new plumbing easier to install

And like OKL I found it hard to read all but a few dimensions, so a bit of guesswork but you will be able to see where I am goin hopefully. You mentioned that the original 4 front rooms from 1920's had timber floors and wriggle room underneath unlike the rooms at the rear.

The following would enable you to work within the existing spaces and still live in the house the new bathroom mudroom could be done first, then the family kitchen area keeping the plumbing as is then last stage New Master suite. Opening up the deck between the garage and family with glass stacker door will add more light and adding skylights will be a game changer. Access to the family bathroom via the deck when arriving home or alfresco living is also good for families.