Underground garden house / barn or garage with address

What do you mean that all questions are resolved? Out of curiosity, since it's not quite everyday, what do you plan to do in there, apart from watching TV? Is it supposed to become a hobby basement to retreat to sometimes, or serve as an apartment? Why underground if it is cheaper and "nicer" above ground?

So, I rather think of the underground "hut" as a preparatory act for the kidnapping. Think of ample ventilation!

In the case described by ypg, however, the ventilation must be made soundproof.

Then we would be back at the bunker,...