[27.Green Buildings]
When we think of green buildings,
we tend to think of new ones---
the kind of high-tech, solar-paneled masterpieces
that make the covers of architecture magazines.
But the U.S. has more than 100 million existing homes,
and it would be incredibly wasteful to tear them all down
and replace them with greener versions.
An enormous amount of energy and resources
went into the construction of those houses.
And it would take an average of 65 years
for the reduced carbon emissions
from a new energy-efficient home
to make up for the resources lost
by destroying an old one.
So in the broadest sense,
the greenest home is the one that has already been built.
But at the same time, nearly half of U.S. carbon emissions
come from heating, cooling
and powering our homes, offices and other buildings.
"You can't deal with climate change
without dealing with existing buildings,"
says Richard Moe, the president of the National Trust.
With some exceptions,
the oldest homes tend to be the least energy-efficient.
Houses built before 1939
use about 50 percent more energy per square foot
than those built after 2000,
mainly due to the tiny cracks and gaps
that expand over time and let in more outside air.
Fortunately, there are a vast number of relatively simple changes
that can green older homes,
from historic ones like Lincoln's Cottage
to your own postwar home.
And efficiency upgrades can save more than just the earth;
they can help protect property owners
from rising power costs.