We live in a multi-family apartment in Israel (just beyond the green line). Our apartment building was built on a hillside so it is setup in such a way that all minus floors (we live on fl. -2) have a chatzer (large yard). We discovered that located directly under our house was a large empty space that we could use for a second story to our apartment if we dug in our yard. Now that we have completed digging beneath our apartment I was warned that we should check whether or not this space really belongs to us or if we would have to share some of the space with the other 20+ neighbors or possibly reimburse them somehow for its use.
A few points to consider: 1. The challal is located directly under our yardapartment with no other neighbors having access to it. 2. We live in a city in which it is very common for people to use challal for their own apartments in a similar way. 3. The city does not offer building permits for using this space so it is widely known that people build without these permits.
I would appreciate any insight that you may have on this including halachic sources or opinions of various Israeli Rabbi’s on this topic if known.
Answer from Horav Y. Fleishman shlit”a
The consensus opinion is that it belongs to all the neighbors. Rav Zafrani spoke about it at a Yom Iyun by us I believe it is printed in the עלון המשפט which is on the Hebrew site-perhaps make a deal with your neighbors since it sounds like there are lots of challals in the bldng