Basement conversion

Hello everyone,

I would like to seek some advice on an idea I have to add value to my property.
I own a large 2 bedroom Art Deco apartment in a block of four in South Yarra. I am on the first floor of the apartment, there are two on the first floor and two on the second floor. There is also a ground floor/basement level with four garages directly under my neighbour's apartment. On my side the ground floor has a courtyard, a small disused laundry/toilet room which I use as a storage room, and behind the laundry room there is large basement area with no floors that mirrors the area size of my apartment above. I am considering doing a basement conversion and ideally turning this disused space into a fifth apartment in the block.

My questions are:
1. Ownership -- the title deed says 'the lower boundary of each of these units lies within the floor of that part of the relevant story which lies within the vertical or near vertical boundaries of the relevant unit' does anybody know what this means? A builder I had through seemed to think I may own the subfloor below my apartment, though probably not the laundry room which is directly below my bathroom. If it is a grey area who could I go to in order to sort out a boundary dispute?

2. Buying out -- if I have to pay out the other three owners for the laundry room and courtyard what would be the best way to offer a fair price? How would I go about getting the title amended etc. and what costs are involved? Would it be difficult to get this put on a separate title as a fifth apartment and how much value would it add as a separate apartment vs on the same title?

3. Planning and permits -- who would I need to speak to in order to get the conversion approved in advance so I don't waste money on an unapproved development?

4. Building and excavation -- any idea what a builder might charge to do the conversion and how long it would take?

Any other considerations you think I should be aware of?

Thanks for your advice in advance.
Dunno about the basement as a appartment

My understanding is that Basements typically cannot be habitable under building code.
Meaning, they can only be used for storage or a garage.

Legally, you cannot have bedrooms, lounges, games rooms etc as there is not enough natural light.
Thanks Ulvit. To clarify, I would be looking at getting windows installed in all of the living areas and bedrooms. I imagine I would need owners corp approval for this but as long as the windows can't be seen from the outside (they would be on the back wall) then I am hoping they won't be able to withhold approval for that...
What he is referring to is that there is a minimum height for a habitable room which is 2400mm - between ceiling and floor.

So many conversions of basements are not allowed as there simply isn't that height available.

I suspect you only own your apartment not the section underneath but it is probably a town planner you need to speak to. If you do own it then you may not be able to build another dwelling down there because it would be over the density allowed on the block.

I think you need to first talk to a town planner who can ascertain your title.
Any work on the building may trigger a complete BCA upgrade to the building - the other owners won't be happy.

Is this building under company or strata title?

As pointed out above, ceiling height, daylight, ventilation, parking and zoning are all considerations with the proposal.

The likelihood is that the area below your floor is common area and not part of your unit.