Shearing layers is a concept coined by architect Frank Duffy which was later elaborated by Stewart Brand in his book How Buildings Learn: What Happens After They?re Built (Brand, 1994), and refers to buildings as composed of several layers of change.

Description

The Shearing layers concept views buildings as a set of components that evolve in different timescales; Frank Duffy summarized this view in his phrase: ?Our basic argument is that there isn't any such thing as a building. A building properly conceived is several layers of longevity of built components? (quoted in (Brand, 1994)).

The layers are (quoted from Brand, 1994):

• Site - This is the geographical setting, the urban location, and the legally defined lot, whose boundaries and context outlast generations of ephemeral buildings. "Site is eternal." Duffy agrees.
• Structure - The foundation and load-bearing elements are perilous and expensive to change, so people don't. These are the building. Structural life ranges from 30 to 300 years (but few buildings make it past 60, for other reasons).
• Skin - Exterior surfaces now change every 20 years or so, to keep up with fashion or technology, or for wholesale repair. Recent focus on energy costs has led to re-engineered Skins that are air-tight and better-insulated.
• Services - These are the working guts of a building: communications wiring, electrical wiring, plumbing, sprinkler system, HVAC (heating, ventilating, and air conditioning), and moving parts like elevators and escalators. They wear out or obsolesce every 7 to 15 years. Many buildings are demolished early if their outdated systems are too deeply embedded to replace easily.
• Space Plan - The Interior layout--where walls, ceilings, floors, and doors go. Turbulent commercial space can change every 3 years or. so; exceptionally quiet homes might wait 30 years.
• Stuff - Chairs, desks, phones, pictures; kitchen appliances, lamps, hairbrushes; all the things that twitch around daily to monthly. Furniture is called mobilia in Italian for good reason.

Theoretical Base

The concept is based on the work of ecologists (O?Neill et al., 1985) and systems theorists (Salthe, 1993). The idea is that there are processes in nature, which operate in different timescales and as a result there is little or no exchange of energy/mass/information between them. Brand transferred this intuition to buildings and noticed that traditional buildings were able to adapt because they allowed ?slippage? of layers: i.e. faster layers (services) were not obstructed by slower ones (structure).

Areas of Application

The Shearing Layers concept has been applied to other man-made artifacts such as software (Simmonds et al., 2000; Papantoniou et al., 2003) or the web (Garrett, 2002).

References

• Brand, S. (1994). How Buildings Learn. New York: Viking.
• Garrett. J.J. (2002). The Elements of User Experience
• O'Neill, R. V., DeAngelis, D. L., Waide, J. B., & Allen, T. F. H. (1986). A Hierarchical Concept of Ecosystems. Princeton: Princeton University Press.
• Papantoniou, B., Nathanael, D., & Marmaras, N. (2003). Moving Target: Designing for Evolving Practice. In C. Stefanidis (Ed.), Universal Access in HCI: Inclusive Design in the Information Society (Vol. 4, pp. 474-478). Mahwah, NJ: Lawrence Erlbaum Associates.
• Salthe, S. N. (1993). Development and Evolution: Complexity and Change in Biology. Cambridge: MA: MIT Press.
• Simmonds, I. & Ing, D. (2000). A Shearing Layers Approach to Information Systems Development

External links

• Big Ball of Mud