So first off, I love basements, its almost like a fetish. Ook.. so this guy is selling a basement in his building and its perfect(got good water, electricity, comms, location and cheap!) except for the fact that the ceiling is 2m from the floor, since I'm 2m tall that is a problem.
I asked him whether I could smash the floor and put a new one maybe 10cm lower, he said I can do whatever I want for all he cared and as far as he knew, there was nothing important underneath.
Ok so now I'm thinking big! Maybe go ahead and lower it by 40cm? or 300cm? Dig another floor underneath the building!
The floor is 40m2 and the concrete is ~8cm thick according to him. The brick walls should go down another 20cm underground. How realistic would it be for me to do that? Could I leave some space between the walls and the new floor shape to dig extra low? Obviously I'd get some help and I know a guy who knows a guy who has a jackhammer.
Best Answer
The concerns I'd have -- outside of whether there's anything under the floor that could be disturbed, and whether there's a rock layer under the floor that would prevent your lowering it -- would be:
You're going to have to make sure this doesn't disturb the foundation. I'd suggest getting an engineer's advice before doing anything.
You're going to have to dispose of all that rubble. That means renting a dumpster, and hauling it out of the basement. Not impossible -- a friend of a friend put a basement under an old farmhouse by digging outward from the root cellar, putting the house up on jacks as he went, and then getting a foundation installed under the house, and he did almost all of the digging and hauling himself -- but it's a nontrivial amount of work. You're going to be moving several tons at least.
Putting in the new floor is going to require establishing a good seal against water infiltration between it and the foundation walls. Again, I'd suggest getting an engineer's advice.
So: Yes, theoretically it can be done. Personally, given the cost and effort and potential liability involved I wouldn't consider doing it on property I didn't own. And I definitely wouldn't consider it without expert advice.