Did You Know?

You may be familiar with the policy that historic sites must be at least 50 years old to be listed in the National Register of Historic Places. But did you know that structures designed by living   architects are ineligible?

We didn't either, until we started digging. Paul Lusignan, a historian at the National Register, explains that no regulation prevents buildings designed by living persons from being listed, but official policy largely prohibits it.

The concern? That sites might be chosen prematurely before an architect's full career is understood. And that nominations become a "pat on the back" to honor architects or help them market themselves.

There are exceptions, Lusignan says. Philip Johnson's Glass House, a National Trust historic site, made the grade because of its far-reaching influence on modernist architecture.