While New York City is recognized around the world for its 20th century skyscraper-filled skyline, it is predominantly a 19th century city, architecturally speaking. Much of New York’s architectural distinction derives from its rowhouses. Often referred to as "brownstones," NYC's rowhouses are, in fact, widely varied and include countless different styles. These standard, narrow, three-to-five story residences which were constructed to house an expanding middle class population more than a century ago. These distinctive residences are the dominant building type in the majority of the City’s historic districts, and their care and maintenance have a substantial impact on each neighborhood's unique character.
There currently are more than 100 historic districts throughout New York City, all of which are as diverse as the owners and residents who live in them. They encompass a variety of styles, from the simple brick buildings of Ridgewood North Historic District, Queens to the elegant Beaux-Arts limestone maisonettes of the Upper East Side and the ornate Queen Anne and Romanesque Revival style 19th-century mansions and rowhouses of Crown Heights North in Brooklyn.
In NYC, The Landmarks Preservation Commission (LPC) is the Mayoral agency charged with designating and regulating these districts, as well as stand-alone landmarks. In order to protect these special properties, the Landmarks Law requires their owners to apply to LPC to obtain permits for certain types of exterior work before the work begins. The decision to issue a permit rests on whether the proposed work is “appropriate” to the character of a building and/or the surrounding district.
Specifically, the LPC must give advance approval to any alteration, reconstruction or demolition affecting a landmarked property. Approval by the LPC is required for any exterior work, except for routine maintenance or repairs, such as replacing a broken window pane or removing small amounts of graffiti. Interior work to a landmarked property generally does not require LPC approval except when: (i) the work will affect the exterior of the property; (ii) the interior of the property has been landmarked; or (iii) the work affecting the interior of the landmarked property requires a building permit.
Examples include changing exterior paint color, porch style, door and window frames and treatments, and much more - specific info can be found on the LPC's website, where manuals based on property types and locations are available.