N.Y.C. Admin. Code § EBC D1004: D1004 Means of egress (MDL 67(6), 67(7)).

Existing means of egress in compliance with Section 67 of the MDL shall be permitted to remain.

D1004.1 Increase in height or number of units.

Neither the height of the dwelling nor the number of units shall be increased unless all units in the dwelling are afforded 2 independent means of unobstructed egress located remote from each other and accessible to each room, apartment, or suite, 1 of which shall be an enclosed interior fire stair. The second means of egress shall be permitted to consist of any lawfully installed means of egress, including a system of fire escapes or exterior fire stairs. See Section D1004.3 for limitations on the installation of new fire escapes.

D1004.2 Increase in number of rooms (MDL 9(10)).

If any HEXA is altered so as to increase the number of living rooms by more than 20 percent, the dwelling shall be altered to HAEA (2008+) and shall be subject to the requirements in Section D303.

Exception: Where the stairs are in compliance with the provisions of Sections D702.8, D703.6, and D703.7.

D1004.3 New fire escapes and exterior fire stairs.

New fire escapes shall be permitted in accordance with requirements of Section D306.3. New exterior fire stairs shall be permitted in accordance with Chapter 10 of the New York City Building Code.

Exception: For buildings erected prior to April 5, 1944, exterior fire stairs shall be permitted to exceed the height limitations in Section 1026.2 of the New York City Building Code, as applicable, where the commissioner finds a practical difficulty in complying with the provisions of Chapter 10 of the New York City Building Code and the portions of the building relying on such fire escape or exterior stairs are provided with a full system of automatic sprinklers.

D1004.4 Access to existing fire escapes from public halls.

When access to an existing fire escape is provided from a public hall by a window or door, such window or doors shall have a fire-resistive rating of at least three-fourth hour.

D1004.5 Variation.

Nothing in Section D1004 shall be construed so as to limit the ability of the commissioner from issuing a variance relating to egress in accordance with Section 28-103.3 of the Administrative Code.