Your budget will define your options. First floor extensions to Californian bungalows are automatically an expensive option due to the structural costs. The original structure was not engineered to support the weight of an additional floor, so the existing house will need some re-inforcement.

Apart from the cost aspect you need a sympathetic designer who understands the style of the home. Too many Californian bungalows have lost their original charm by cheaply designed, unsympathetic boxes plonked on top and behind.

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Without a design it is hard to be precise about costs but I would anticipate that you will be well into the six figures, so be sure about how many hundreds of thousands you are prepared to spend before you engage a building designer. To be honest with a small block and a house that requires an expensive first floor extension you may be better off considering your moving options....

Best of luck with your budget,

Dr Retro of Dr Retro House Calls and Dr Retro Virtual Visits

Dr Retro is the expert for a reason !

I suspect your existing place has already been rejigged at least once , and is a compromise anyway . A 2 metre wide dining area is almost unusable IMO , the bedrooms are small , and yet there are effectively 2 fairly large lounges ! One is a /slash dining too , but see what I mean about compromises . And the larger lounge is only accessable through the other lounge -- wotkable , not great for guests , and sort of makes 2 lounges redundant .

I'd suggest getting a structual engineer to check out which walls can be easily removed without losing strength , and almost start with a clean piece of paper -- add a 2nd bathroom or bigger bedrooms or 1 lounge -- start with the idea that no idea is too silly , and then work out the really silly ones haha .

Actually , taking that approach , and without knowing where North is , or views etc , but maybe this will get you thinking .

Move the kitchen i.e. all new cabinets , in the existing front living room , maybe the sink etc where that front window is ( the window may be too deep , I'm just throwing an idea out there ) , with the dining behind , the lounge in the existing lounge .

That middle bedroom is marginally the largest , so just an idea -- what is now the kitchen may be able to become 2 bathrooms -- one an ensuite by adding a door through to Bed 3 . The water and waste are already there , space not too much of a problem , etc .

Presumably you don't want a 3rd bathroom , so 'that' corner may become the laundry , and what was the laundry and rear dining maybe a small lounge or study or play room or wet area or whatever .

All that without removing a wall , it wouldn't be real cheap , but at a guess it could be 1/4 the price of adding a second floor !