Contested resources

The solar energy that today lands wasted on thousands of acres of deteriorating San Francisco roof membranes will in the future be treated as a hotly contested resource. Rooftops will have to be thoughtfully partitioned, with sunlight allocated in proper proportion to roof gardens, interior daylighting (skylights), photovoltaics, and solar hot water (though increasingly efficient PV panels are making it less expensive to heat water with electricity).

With this increase in attention, roofs will likely also become more common as extensions of living space, with a semi-isolation like that of the back yard—refuges in plain sight. Whatever the use, the increasing cost of urban real estate will not allow such a resource to remain vacant for long.