BY LAURA KUSISTO
Some of the happiest office-building landlords these days have been owners of loft buildings in Chelsea, Hudson Square and the Flatiron District, which are in high demand among media and technology tenants.
But this demand is forcing out some of the traditional tenants of these neighborhoods, like nonprofits and arts groups. With rents rising and vacancy falling, they’re calling up movers and heading for less expensive quarters, sometimes to areas such as Brooklyn and Queens.
At least a dozen prominent organizations, including Theatre Development Fund, Harry Fox Agency, Arup and Whispr Group, a social-media company that does work for companies …
