What type of slab do you have? Unfortunately there is a wide usage of waffle slabs in project homes. These are unsuitable for a second story.

I don't know if this refers to slab type but the engineers report says "reinforced concrete raft footings continuous trenched or piered 200mm into natural ground"? I do remember we asked the builder if it would be a waffle slab and they said it wouldn't be (so hopefully it is not) :)

I’m really really not an expert but the “raft footings” sounds positive while the “piered 200mm into natural ground” may not. You can’t do any further planning until you determine what type of slab you have. While you’re doing that, you should also check your Council’s requirements for set backs for upper stories and anything else that may be a hurdle to you. Are there any houses in your area that have done a second story extension? You can ring the Council and ask.

Having a read again. I think your timeframe may make the extension not fit with your long term plans. You mention that you are looking for a 5year solution. Given you are starting from scratch an extension from now until finished is going to take about 2.5 years. Factor in the 8-12 mths of building inconvenience, assuming you can continue to live on site (and you can’t always) where you have days without water or power and eternal dust and dirt. Are you the type of person who can cope with getting woken by tradies coming through the door at 7.30 and having no hot water for a shower and having multiple people in your kitchen while trying to grab some brekkie? If you live off-site -and you may need to for efficiency and/or insurance and/or mental sanity- then you need to factor in the cost of rent, utilities and insurance at two properties, and removal costs. And whilst we are talking money what type of budget do you have in mind? Smaller extensions have a higher per square metre cost than larger ones and second story are more expensive again.

unable to read all the dimensions but assuming a narrow block of land with zero set back on the garage you would lose extra width upstairs with the additional setback needed for upstairs, none of your examples could fit the available space and there would be a lot of wastage upstairs and down with hallways and stairs and, if a suitable plan could be achieved, there would also be substantial costs ($10,000?) in council, design and plan drawing fees plus costs of living elsewhere for months to build a second story and an upstairs would not improve modest downstairs living and outdoor areas...my suggestions would be to make improvements without over capitalising and could be achieved in stages eg new laundry and move meals storage, (nb this allows the old laundry to continue to function pending completion of new laundry) rearrange bedrooms and replace old external laundry door with window and cladding, enclose the alfresco with insulated wall and cladding), move sliding glass doors and use windows to suit direction of sunlight and outlook in new family room and add a tiny handbasin (inside the wall) to the toilet and, although it's not legal to use a garage for living areas, consider a partition to create a storage area (keeping the garage door) and make a rumpus room with skylight in the garage and leave cars outdoors...these changes creates 4 bedrooms, bigger study, new laundry with storage and a much shorter inside walk to outdoor drying area, generous dining and family room and you could add paving outdoors with a giant market umbrella to replace the alfresco ...unfortunately you will still be astounded at the cost of any changes but hopefully a staged approach would make these changes manageable and you could save more with DIY freestanding flatpac wardrobes, family room and study furniture and your carpenter/ builder might be happy to credit some costs for help with demolition under supervision

Thanks so much for the detailed replies. Really helpful considerations! Really appreciate it.

Bigreader:
Re: timeframe, that is a very good point. I had underestimated how long the porcess might take and really when you put it that way it's a lot of cost and effort for a relatively short timeframe. 

Re: Budget, wouldn't want to spend more than 200k or I think we would be overcapitalising, but even if that was not an issue I'm realising that the timeframe and hassle probably makes this not worthwhile.

There are a few second storey extensions in the neighbourhood but on much older homes/bigger blocks nothing recent I'm aware of. 

You are probably right about living on-site too, especially if it drags on.

Oklouise
Thanks so much for drawing this up! It's really opened up my mind to some new possibilities. You're right one of the main issues with this house is the small living/dining area (which won't be fixed by upper extension) so even if we didn't get as far as changing the laundry/bedroom situation even extending outwards under alfresco would add significantly to functionality of house (especially as we don't use Alfresco much) to help us last a few more years here with a toddler and big dog and probably not overcapitalise. 

Our neighbours have done the same with their garage (rumpus/storage behind garage door). Our car is out anyway as I had to give up and turn the garage into storage area despite best efforts with decluttering. 

Anyone had any experience with enclosing an alfresco in terms of costs/timeframe? The alfresco slab was poured seperate to main slab not sure if that would be a problem?

check with neighbours to ask about who did their alfresco changes and ask for several quotes...

For 5 years , have you thought about putting a door or large window on the front of the garage , and ( depending on ages and sexes ) have 1 , 2 , 3 children sleep there , set up a study space , a temporary wardrobe or older wardrobe ? It depends on a lot , including ages and attitudes , and 5 years is a while for someone who is say 8 , but I'd doubt you'd get any change out of $200-250k adding upstairs ( Maybe more if downstairs has high-end finishes and you match those ) , and it could look good , or look like an obvious add-on -- in other words , you probably won't get your $$$ back .

Changing the garage use isn't ideal , but I can see lots of hassles adding upstairs too .

Glad we could help with different view points. For the Alfresco you could get a quote on all weather blinds even better if they are motorised. Blinds combined with some exterior heaters, ceiling mounted for safety, could give you some breathing space. They would add value to your existing house in a way a temporary built-in solution may not.

Adding a second story to your house is definitely possible. Still, it's easier to say for sure with more information about the specific building regulations in your area and the structural design of your home. However, it is often more cost-effective to expand your current home rather than sell and buy a larger one, especially with the current housing market. It's great that you like the area and wants to stay there longer. And by the way, The Continuum Condo http://the-continuum-thiam-siew.com/ looks like a great place to live - thanks for sharing the link. Good luck with your decision-making process!