Of all architectural features, only the roof is essential. The need for shelter, being the most basic need in building, is expressed most clearly by the roof. In relief programs after disasters, provisional shelter is created with tents. A tent is by far the best temporary building as it is purely and essentially: a roof.
For whatever motivation people are migrating, making a roof is the start of settlement. Whether we go out from a luxurious villa to spend the weekend on a campsite, or we go from the countryside to whatever scrap of land available in the big city to build up a living, our putting up a settlement starts with making a roof.
The purpose of a roof is to protect us from the weather. Sun, rain, wind, and cold can all be kept at bay with a roof. A miniature version is the umbrella. If big enough, it will keep us dry as it makes the rain fall in a circle around us. In a crowded situation, the water of our neighbour’s umbrella may fall upon us. Likewise buildings that are directly built to each other, have to deal with rainwater in a collective way.
A proven technique to keep the water out is roof tiling. A roof tile in a sloped position drains the water to one side: the lower. As long as the next tile is below the first, it will do the same and with many roof tiles together, a long path is created to drain the water to the side of the building. Thus, the individual structure of each roof tile is contributing to the accreted structure, the roof. The same principal is used for corrugated asbestos-cement sheeting.
In dense built-up area, such as the informal settlements in Dharavi, an incredible phenomenon can be seen. Not only are individual buildings protected by roofs, made up with the overlapping tile principle. The roofs themselves are in a similar cohesion with the neighbouring structures. Actually, a whole area is protected by putting the roofs in an order that drains the rainwater all the way down to the outside rim. The incredible thing here is that we think such an intricate system can only be achieved through meticulous planning. The informal settlement, considered unplanned, is nevertheless capable of generating such accreted structures.