Most people would agree that the longer lifetime a product has, the better it is for the environment. A product with longer lifetime is requires less replacements, which gives less waste due to production and less emissions. But does it mean that the product is more environmental friendly? The answer is not always obvious.
According to Wikipedia, the design life of a component is “the period of time during which the item is expected by its designers to work within its specified parameters” . A normal design life or life expectancy of a building is between 50 and 100 years. Design for 100 years requires more resources than a building with shorter life span. The increased resource use during production may pay off through a longer lifetime. However, it could also prove to be money and resources down the drain. Today we see many of the office buildings built in the 60’s and 70’s being demolished or striped. They have become obsolete because of new technology, new requirements or changed use.
Accounting for obsolescence is not only important when designing buildings. As Georges Doriot once said, “Always remember that someone, somewhere is making a product that will make your product obsolete” . Good examples are phones and computers. They are frequently replaced, not because they are worn out, but because new technology makes them obsolete quickly. A mobile phone with a 5-year design life is not environmental friendly, because longer design life increase energy and material use in production. This is waste because the average phone is replaced after 1.5 years anyways .
Planed obsolescence? 
Estimating the correct service life and designing products accordingly is very important considering both economic and environmental factors. However, when designing a building the service life will never be more than an estimate. It is equally important to make the right decision of when a building has become obsolete.
Obsolescence allows for new and less polluting infrastructure, as well as reducing costly operation and maintenance work. Not allowing for new infrastructure will also block development of new technology. However, replacing buildings will generate large capital investments and increase short-term resource usage and pollution.
Choosing the right design life and deciding when replacement of infrastructure is due is difficult. Nevertheless, they are important decisions, and blindly designing for maximum service life is not the way to go.
 Wikipedia (2013) Design life. Onlie: http://en.wikipedia.org/wiki/Design_life
 Lemer, A. C. (1996) Infrastructure Obsolescence and Design Service Life. Online: http://www.ce.cmu.edu/~hsm/im2003/readings/lemer-jis-96.pdf
 Tran, P. (2013) Average Life of US Mobile Phone is 18 Months. Online: http://www.mediabistro.com/appnewser/33775_b33775
 Hamill, H. (2013). Online: http://www.hasroh.co.uk/archive/cgi-bin/cartoon.pl