Re: does the landlord refund you all the money you gave to pay the rent? @Jess
I'd say more like 'the new bathroom you started to have fitted'.
You'd expect to enjoy your new bathroom if you stay in the house after it's completed, but lose any rights to it if you move out.
If you have a good relationship with your landlord you might get some sort of recompense for the work you've put in. Good luck if you've spent the last 40 years complaining about the house and how mean he is.