I am moving to an older apartment building in Yerushalim. The neighbor downstairs built a 40 sq meter binyan kal (tin roof) for a yechida (rented to newly married couples) on his backyard. Our balcony is connected to this yechida and we are considering asking him to extend our balcony on top of his yechida for a deck patio, not enclosed, for a larger marpeset pergola area. How do you recommend we ask him, should we offer to compensate? Should we first ask permission, are we allowed to ask?
It is very good that you are asking, because such situation often cause neighbors to fight, and taking an approach of keeping the peace, is the best route.
The first question is, are you doing this with a permit from the municipality? Check with your friends and neighbors, it might be required, or else you run the risk of them knocking it down. In order to get a permit, you will need the permission of the neighbors.
Aside from this, depending in the size of what you are building, you may need support beams, which will be in his property, or worse they might have to dismantle part of his yechida to do this. For that, you will need his permission. If any of these things are needed, you definitely should offer compensation, as it is inconveniencing him, and most probably damaging too.
First get tentative plans from and architect/engineer of what you are planning to do, and how it will affect your neighbor, then you can approach him, and ask his permission. Any damage that is done, you understandably must pay for. Additionally, it is a god idea to offer compensation for the inconvenience of the actual building. Adding something to his building, can serve as a compensation, but you have to discuss this with him.
It will end up costing you more, but if you consider it part of the building expenses, it will make it easier to swallow.
Hatzlocha Rabba with your building, and everything should go b’shalom.