Lauren Quinn has an interesting article in The Guardian about Hanoi's approach to unlicensed, unplanned construction. Here's an excerpt:
As the 1990s progressed, increased wealth fuelled demand, and illegal construction grew sharply. In 1995, there were about 1,000 illegal projects in the city—and those were just the reported cases. The city also began to spread out, progressively consuming villages and rice paddies to keep pace with demand for homes. Urban planners call this "spontaneous urban development." Most of the world calls it "slums." But in Hanoi, with the unusual mixture of basic regulation and control, a strange thing happened. "The negative side of this development was substandard infrastructure," says DiGregorio, "but there was also a positive." That positive came from the enlightened regulatory attitude of authorities.
In the culture of semi-legal construction, if someone built a structure that adhered to minimum standards, it became legal—and for the most part was provided with basic services such as electricity and sanitation. In most developing cities, those flooding from the countryside end up living in sprawling squatter encampments, lacking basic sanitation and vulnerable to eviction. But in Hanoi, the new arrivals could build houses that didn't have official permission but often received basic services anyway.