On the other side of the wall of our machsan there is a chalal. We are the only ones who theoretically could have access to the chalal. Do we only need permission from the tenants on our side of the building or all the tenants in the building in order to take down the wall and make use of the chalal. Do we have to offer monetary compensation?
In principle, the chalal belongs to everybody, and you don’t have the right to take it for yourself without the other tenants’ permission. See the last section of the article here.
However, in certain communities and buildings, the custom is that the person will unique theoretical access is the one who has the rights to the chalal. I have been informed that this is the case in Beit Shemesh, and other places.
Certainly, if other tenants have taken their own chalalim, and have therefore ‘taken their share,’ you would also have the right to take your ‘share.’