He—may Allah have mercy on him—was asked:

What is the ruling concerning someone who leases land and builds on it a house, a shop, or another structure that, when developed, would command twenty dirhams in monthly rent, while the monthly ground rent payable is one and a half dirhams?

He had previously withheld judgment:

May the tenant build a mosque for Allah alongside the property he has already built, and dedicate that property as an endowment for the mosque?

He answered:

He may dedicate the building he has erected on the leased land as an endowment, whether as a mosque or otherwise. This does not extinguish the rights of the landowners. Once the lease has expired and the building has collapsed, its status as an endowment ceases, whether it was a mosque or otherwise. The owners may then reclaim their land and make use of it. As long as the building remains standing on it, the fair rental value is payable.

If someone were to establish a mosque as an endowment above a residential property or a house, and the house or residential property subsequently collapsed, endowing the upper storey would not extinguish the rights of the owners of the lower storey. Likewise, endowing a building does not override the rights of the landowners.