Generative Codes for Living Neighborhoods

By Christopher Alexander. Original post here. Published at P2P-Foundation on 6th April 2015.

A generative code is a system of unfolding steps that enable people in a community to create a wholesome and healthy neighborhood. The steps are governed by rules of unfolding that are not rigid, but depend on context, and on what came before. The rules work in a way that is similar to the rules that nature follows to unfold an organism or a natural landscape, much as genetic codes unfold embryos. But these rules unfold a neighborhood and its buildings from the whole, and lead to a unique result for each particular place.The rules tell you how to take specific steps, in a certain way that allows unfolding to proceed.

• Like patterns (identified in A Pattern Language, 1975), the rules cover a great range of scales — all of the major features of the neighborhood, down to the finer details, including open spaces, buildings, connecting paths, rooms, window sills, etc. 
• The rules are ordered – sequenced – to unfold each part of the environment being created, smoothly and coherently. 
• Also, in the generative code, each rule is specifically tied to a certain group of individuals, whose job it is to undertake that part of the unfolding together. 
• Finally, in order to make the process succeed, the overall operation of the unfolding, which goes forward step by step, is accompanied by a general set of practical specifications for the conditions governing land tenure, cash flow, and human organization, and the community in which the process is being carried out.

When a generative code is used, the order in which things are done plays a decisive role in proper execution of the unfolding process.

For example:

• Diagnosis of the site is an essential early step. 
• Roads and driveways must be located and built after the pedestrian structure, not before. 
• Roads must be located and built after the houses, not before. 
• Sewers must be located and laid after public space is created, not before. 
• When houses are designed, the garden must be placed (located) before the house volume is located, not after. 
• Construction work must begin long before final drawings are ready, and the drawings develop, in parallel with the construction process. 
• Windows must be placed, designed, and measured and built, after the walls or wall framing has begun, so that they reflect the real situations in the room, its light, and view. 
• According to contract, changes of design which have no effect on quantity of units built, must not be viewed as change orders, but as part of the builders obligation, provided they stay within parameters of quantity and price.

In an unfolding sequence, these things occur in this unusual order, not in the order we might expect from conventional contemporary building methods. This is because each activity is unfolding from the wholeness of the place. The changes of sequence are not whimsical, but necessary, to make sure that each thing can be adapted to the whole, in a successful fashion. They are necessary, in order to allow a coherent unfolding, of the neighborhood, where the right things come first, and the lesser ones take their place in the context provided by the major things. The “right” things, are the ones which have the biggest impact on the environment from a human and emotional point of view, which is capable of making people healthy because their deepest feelings are respected.

FOOTNOTE

In order to see the contrast, here is the order in which these things were usually done in conventional 20th-century development work, many of them specified in existing city codes. In current practice, there are many conventions of sequence, which have become part of the accepted wisdom, in planning, architecture, and development.

The following examples are all harmful:

• Conventionally: Roads are built before the buildings they serve. 
• Conventionally: In a tract development, street sewers are laid long before the houses are built. 
• Conventionally: Houses are placed, and the garden is whatever is left on the lot, comes second. 
• Conventionally: Windows are designed and positioned at the time the building’s plans are submitted for plan check. 
• Conventionally: Drawings are completed before any construction work is done. 
• Conventionally: Neighborhood plans are completed, before any construction work is done. 
• Conventionally: Public spaces are designed after individual buildings. 
• Conventionally: Changes are done by change orders, and therefore become very expensive.

These practices do not support the creation of living neighborhoods.