Lowering a concrete floor

Surprised this one hasnt been mentioned before but nothing found in a search.

We have a highset house, single skin brick and pier below, with an inset slab. We're thinking of fitting out the lower floor, which is currently just a couple of garages, a bathroom and a lot of empty space. The council seems to have no great objections, as long as we conform to the std building codes. The stumbling block is the internal height. After fitting a floating floor and a ceiling, the finished internal height should be about 2300mm. The council says we should be able to get permission to put a kitchen, bathroom, laundry and rumpus in this, which is actually a pretty good result if we can slip a dining room into the 'kitchen' area. To put a proper loungeroom or bedroom in instead of the rumpus it would have to be 2400mm. I would much rather leave the option open to put anything we want in, and anyway I dont like the feel of low ceilings - I'd like it to be at least 2400mm just from an aesthetic point of view. The upstairs is 2700mm so I dont want an underground dungeon effect.

I am vaguely aware that there are two ways we can deal with this. One is to remove the current slab and replace with a lower one. Actually, this has already been done over about a quarter of the area because the previous owners had a large caravan, so some of the floor has already been taken down about 200mm (remember its an inset slab, so I presume it just needs to be broken up and carted out - maybe ????). The other option is to lower the top of the slab by cutting and grinding the top off. I dont know the thickness of the slab, but I think its very thick judging by the aforementioned lowered part, and also because the previous owner seemed to have been in the habit of doing things right (at least when other people were doing the work), if not overbuilding.

My question is does anyone know about this type of work. Is it practical? a common solution? What issues are involved? Are there alternatives? Anyone had it done??? Costs???? Any information at all would be appreciated.

Standard caveat applies - I'm intending to get professional advice when the time comes, and someone else to do the work - I just want to start building up my knowledge before getting people in. I realise work like this is not cheap, but in the scheme of things not worth skimping on.

Cheers
Arron


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