Alison, OK there's a fair bit there to work through and digest. You've clearly got a plan in mind, however how that stacks up practically against the numbers is the question. The thing is $700K seems like a lot/healthy amount for a renovation. It may or may not be depending upon the solution and how far it needs to be distributed over existing house and developed/extended areas. Right out of the gate I'd suggest that if you're spending that much then arguably the garage is smack bang in the wrong position, and needs to be moved, which adds something else/more cost into the equation. You don't want to be working a design around a poorly positioned garage unless that's the only option for it. When you go up a level yes it costs more but the question here would be exactly would be best positioned upstairs. Would it be kids zone or Master Zone? When it comes to staging projects then bear in mind you pay a premium for this and it never is the cheaper way to go. Think an additional 30% give or take for breaking it up into smaller scope projects and increasing costs over time. You may find that your 700K project in one bite equates to a $1M project in two stages over 5 years. Its ALWAYS better to do as much as possible as soon as possible for a long term investment scenario. It also is one thing to stage a clean rear extension without changing much of existing vs an upper level extension that is invasive in nature and requires essentially comprehensive lower level renovation at the same time to achieve. Then there is the cleaner 2 story rear extension that may avoid going over existing, but might look a little unbalanced and be less ideal in regards to overshadowing to your outdoor areas. Lots and lots to consider and weigh up here.

There are really no easy quick answers here. To get closer to the answers you seek, practically you require the services of a design professional who is particularly experienced in renovation/extension scenarios to assist you who can provide not only options but also has the capacity to apply associated and accurate cost projections on these options. Without costings, any "option" is pretty useless as an isolated idea. Yes it's a possibility, but it's only half of the picture. This is exactly what we do as a first step of service, what we call a "Feasibility Stage" to help people work through these types of situations, so the client can properly understand the both the design and relative cost consequences simultaneously across some alternative/various options (say single level vs two level, single stage vs 2 stage, "ideal/dream" scenario vs more "conservative/scope reduced scenario). You require the accurate information to be able to move forward with the type of decision-making. Any design ideas without any form of associated cost information, are arguably random/arbitrary and I'd suggest little use if not potentially misleading. In order to be appropriately rationalised, you need costings coupled with a specific design solution, considered in context, with understanding of any relevant existing planning or contextual constraints or features. There is always then the possibility of prioritising of say size over quality, in that if you can possibly keep a lid on finishes for the sake of getting more space, then the budget can be theoretically stretched to cover more space. It's always a balancing act between various elements.

There will be numerous ways to achieve this, but what the best option for you will come down to your personal priorities, which of course will be influenced by your financial options and capacity.

It also depends on how you'd be going about the project, whether you'd be doing a DIY aspect or whether it was fully contracted to builder and required financing etc......all things that will influence what is and isn't possible.

I know I haven't given you any clear answers, but my best advice would be invest in some professional service form a local architect or experienced building designer.

Best of luck PD :)

www.pauldistefanodesign.com

Sounds like you have a good idea of where you are going. I will make one suggestion. My kids are now 8 and 10 and we need a separate living room for them. They received a Play Station last Christmas and believe me it’s not something you want in your open plan area. If your kids continue to share a room you may be happy for them to have it in their bedroom but this may not be ideal when they have friends over.

@bigreader thank you for the reminder, I know exactly what you mean.

@Paul Di Stefano Design thanks, I have a feeling I should invest in a detailed feasibility study. You're right, there are many possible design options, many possible ways to go about things. For instance, one other option we're considering is to leave the existing house untouched (in phase one); add the new extension (kitchen+laundry+living+dining, and master+WIR+ensuite, maybe an extra bedroom if Phase1 budget permits), and move in... then do phase 2 (all other renovation/extension) down the line.

And of course there seems to be a possibility we might not be able to do everything we want within our budget, in which case we could either pass on buying this property and try to buy something else...

Regarding the garage, current zoning requires 1m setback from side boundary, I'm not sure this can be waived? If it can't be waived, removing the garage means no undercover car parking, and we would definitely prefer to have at least one undercover (preferably garaged) car park.

I would consider repurposing the garage or knocking it down. The last stage should be putting a new single garage beside front bedroom with roller door at each end. You need access first for extension.
Central bathroom to go to extend hall.
Where does the slab extend to and the double brick?

my suggestions would be to first add a new family kitchen guest room and bathroom: about 70sq m slab on ground, then add new laundry, remove central bathroom and refurbish all the hallways, replace old kitchen with new ens and wiw, replace family bathroom, refurbish all the other rooms and add outdoor entertaining areas without blocking sun to family room..i would keep the garage as is (removing may prevent replacing a similar size anywhere else on the block) although you may be able to add a small mancave at the east end of the garage if/when you need the MPR for MIL or need the MPR for an office if/when the boys don't want to share...i've kept the old toilet at the end of the new laundry as there isn't an alternative space for a separate pwd room in the original house and keeping all the original walls means the bath fits much better in the family bathroom not the ens and, assuming that there aren't too many surprises, the basic concept looks good although the boys may be a little further away than you would have planned but by the time the new bedrooms and bathrooms are finished they'll be so much older