Law of Unintended Consequences

SF is seeing a dramatic rise in pedestrian and bicyclist injuries and fatalities as more people walk and bike instead of drive their cars. Obviously there is nothing structurally incompatible about pedestrians, bikes and cars sharing the roads so this issue can be dealt with through existing law enforcement and public information campaigns (seriously, pedestrians walk around SF as if cars never existed but I have yet to see a conflict involving a pedestrian and a car where the car came out the worse of the two.)

The number of pedestrians and bicyclists injured on the streets of San Francisco spiked in 2007, and overall traffic-related deaths jumped more than 40 percent from the year before, according to new data from the California Highway Patrol.

[From Spike in S.F. traffic deaths, injuries]

Reading this reminded me of another example that effectively demonstrates how our world is formed not out of individual entities but rather systems that interact. Change one variable and something over there that you didn’t anticipate flares up.

In the 1980’s a move was started in the construction industry to use materials like Tyvek to wrap new houses during construction in order to achieve air tightness for insulation value (R value) and to contain moisture penetration that causes dry rot (ironic that dry rot is caused by wetness).

House wraps and other new technology insulation are widely used today and considered good building practice, indeed required by building codes. However, there was one unintended consequence of house wraps that we have paid a very high cost to deal with, mold.

As builders wrapped houses tightly and combined them with other energy saving features, such as 2×6 walls, they not only decreased the potential for moisture to enter a structure, the made it difficult of moisture inside the structure (like moisture contained in the air) to leave the structure and the result is that the multi-billion dollar explosion of mold claims correlates strongly to new building techniques adopted in the last 25 years.