Illegal construction

Illegal construction or building is construction work (or the result of such) without a valid construction permit. Besides the potential technical hazards on uncontrolled construction sites and in finished buildings, illegal building activity can be a major environmental violation when the works encroach upon preserve areas like nature reserves. Likewise, illegal building can have serious political implications when it is practiced as landgrabbing or for illegal settling in foreign territories (see e.g. International law and Israeli settlements).

Illegal building can be the consequence of a combination of urbanization, overpopulation, homelessness and poverty in which case expanding slums, Shanty towns or similar will result. On the other hand, illegal building activity may be due to profitable speculation with and exploitation of valuable real property. Demand for mass tourism accommodation (hotels, etc.) as well as its counterpart, individualistic luxury retreats for the very rich are visible drivers of such speculation. Similar motivation may come from incentives connected with the illegal construction of great shopping malls or similar on greenfield land.

...
Wikipedia