"In a slum, one can often not afford the luxury of demolition. Building a larger home usually means extending an existing house by a floor on top. Choices from the past remain visible and set implications for further development. Continued building means puzzling with the existing situation. The current situation imposes restrictions on the new design. It requires much creativity and inventiveness to get all connections, both spatially and technically, of old and new quite right. Design issues and building projects are therefore in a slum more complex than average. As a result, especially proven techniques are used. Style architecture makes little chance. Avoiding risk is crucial, because of financial constraints. In his book How Buildings Learn1, Stewart Brand shows how not only the initial design determines the shape of a building, but also how the subsequent existence leads to growth and change. In a slum, especially that growth and change are built, not style and originality.
[...] Although an architect will never design a slum, the architecture of a slum is an essential source for designers."