Links to their permits and property tax records.

Here are links to official information on the Zwirner's house from NYC.gov:

232 East 13th Street Building Information and Property Tax

234 East 13th Street Building Information and Property Tax

And while I'm at it, here's that article on David Zwirner's house from the New York Observer:

But he’s been quietly expanding elsewhere too, recently paying $3.65 million for a four-floor building at 232 East 13th Street. Conveniently, the place is next-door to his five-bedroom brownstone—which was listed for $2 million when Mr. Zwirner and his wife bought it in 2002. ...the Zwirners aren’t strangers to superb home redecorations. “A complete gut—they totally ripped it apart. One of the most amazing renovations I’ve seen in the city,” said broker Patrick Vernon Lilly about the townhouse he sold the Zwirners in 2002. “They’re the type of people who see real value when other people can’t.”