Checking council regulations and setting the budget will determine what you can do.

Write up brief and keep referring to it. Start an Ideasbook.

What is the easement for, is there a zone of influence.

Staying on a single level is usually the value for money option and most designers would investigate this first before considering a second level.

Try and use the existing walls and rooms as they are. Same with doors and windows, keep them where you can as the build costs skyrocket with the stroke of a pen.

You'll get a lot of advice here as well as from friends/family/etc. but use this information as advice only and don't set it in stone, keep an open mind with what is available as theres many options.

I would engage an architect, building designer or design draftsperson to do the design as they have an intimate knowledge of whats doable and whats not. Each of these professionals offer different levels of service. They all do design and drafting up plans for DA/CC but theres more to it that needs doing....

what are all the walls floors and roof made out of...including the garage? is any part of the house a later addition? is the garage in good condition? is there any useable height attic space? are you allowed to keep the old garage but not build on that space? what is the height of the floor off the ground at the back of the dining room and does the block slope in any direction and some photos of the outside and the roof would help

Extending a home that is attached to another along one boundary is not a job for a beginner. There are so many additional things that need consideration. But perhaps the first is your budget, which may well answer your question about a first floor or ground floor extension due to the substantial difference in cost. Apart from the usual buidling regulations and council requirements (which vary across Australia), it would be courteous to consider your neighbour and how any new work will impact their home. I have seen cases where neighbours of attached dwellings have co-ordinated together for the design and building of a first floor addition with great results.

You need to find a local design professional who is experienced in extensions and your local regulations,

Best of luck,

Dr Retro

of Dr Retro House Calls

as already advised, there are special consideration for an old semi detached house, your local Council regs and the condition of the existing buildings but, based on available info my suggestion would be to keep as much of the original house as possible (otherwise you pay to demolish ...often all the character features of the old house...and then pay to try and squeeze new rooms into spaces that are already better sized for the existing purposes) adding a single level extension with a slab on ground a few steps lower than the main house, using the old kitchen for a family bathroom and laundry (old external door replaced with a window to be able to lose the old external steps) and a separate powder room and hallway squeezed out of the old bathroom...the extension is attached by a narrow link and twin courtyards the new master suite, family dining room, kitchen and side entry with a simple gable roof, raked ceilings and single thickness walls with modern "fibro" cladding and, if possible, it would be great to be able to salvage a basic carport or covered utility space out of the old garage ....this plan has everything you asked for without wasting space on upstairs and the courtyards allow for private views and being at ground level allows better connection to outdoors

Thanks for these wonderful comments everyone! These are really good and provide me with some great starting points.

A few of you mentioned budget. We are thinking 300k to 400k would be good, but I'm not sure if this is too much or too little. We are based in Melbourne if that helps.

We will definitely engage a building designer rather than architect mainly due to costs. The suggestion of a brief is good so that we have a clear idea of what our goals mad requirements are.

Neighbour wise we should be fine :) I hadn't considered asking them if they were interested in renovations as well.

Wow, that plan looks amazing! Can't believe that you create that so quickly. I'm sorry I couldn't get to answer your questions in time.

The easement is for drainage. I believe there is a large drain likely sewer line running down the side form memory.

The walls are all brick. Double brick. Roof is tiled and floors are hardwood timber except in existing kitchen and toilet areas.

I should have added we plan to knock down the existing garage and use the space for backyard. Can't build on it because of easement. The land slopes very gently from the front to the back. The height of the floor at the dining room I would guess is 50 cm higher than the ground outside. I can try and take a photo today.

We were thinking we would try to keep as much as possible of the existing walls, like you have suggested except the bathroom laundry kitchen and possibly dining.

although it would be nice to have the main hallway width wider. but I can see then that you would lose quite a bit of space.

If the existing garage has already been built over the easement (and approved) I would keep it and do a make over as a studio or other, sad to waste something that can be used especially if you aren't allowed to add any other building in it's place.

I would add new carport or garage towards the front of the house with access through it to the rear of the property. Driving down a long driveway to park is bad enough but backing out is a nightmare for some of us.

Also you mentioned removing the fire place which would be a big mistake as thats one of the features that are loved by everyone, keep as much or all of the original features in the main existing part of the house. The fireplace could also cause problems if you did try to remove it as it is most likely matched to one in the neighbours duplex.

I agree removing the fireplace would be sad :(

I had not considered keeping the footprint of the garage if that is possible. it is pretty old and run down so would need to be rebuilt. I guess there could be a small courtyard area where the driveway is now.

photos of the back area below.

Even though the garage is old it doesn't matter, once the foot print has been approved don't lose it as it goes to the boundary thus giving you more space. This is where a good architect/designer is of great help with working with and refurbishing this space as part of the foot print of the house.

I am working on something at the moment which would make the garage your study/office, shouldn't be long and will give you a rough idea for a floor plan working with existing doors,windows and rooms . Single story would be the most cost effective as already mentioned, it's also better for young families and older people

Please do not remove the fireplace. They give so much character to a room, no matter what the room is used for.

A rough idea you could possibly work with trying to keep as many walls and features as possible. It would not only be sad to remove the existing fire place it would be wrong, would love to see a photo cheers