Al-Fusḥah (Concession of Space)

Answer—and Allah grants success: What appears to me regarding al-fusḥah is that it is of two kinds:
1. A temporary concession: when its time ends, the owner of the land takes back his land and what is built on it, and pays the builder the indemnity for his construction.
2. An absolute concession: and the prevailing custom, as it appears to me, is that the builder is not asked to vacate the building except in cases such as when harm comes from th e concession holder—like it becoming a refuge for thieves or drunkards, or the like.
Thus has the understanding of al-fusḥah appeared to me according to the custom among the tribes. The first kind, on this understanding, resembles a loan for use (ʿāriyah), and a loan for use does not entail ownership. The second kind resembles a gift in one respect and a loan for use in another. Its resemblance to a loan for use is in that the builder has no right to sell except to the one who granted him the plot (al-ʿarṣah), nor may he remove it from his ownership except after obtaining his permission; and the owner of the plot has the right to remove the builder from the house when there occurs from him something like what we mentioned earlier, and he pays him the indemnity for his building.
Its resemblance to a gift is in that the owner of the plot has no right to remove the builder from the plot for other than the cause we mentioned, nor to retract the concession, nor to demand rent for the plot.
Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.2