New York Chapter
The Founding Chapter of
The American Institute of Architects
AIA New York Chapter Zoning Study: - Bulkhead Study
24 July 2006
Introduction
The following document, prepared by The AIA New York Chapter, has been
developed to address concerns raised by Chapter members and others about
rooftop obstructions permitted for new residential buildings in New York City. The
current limits on rooftop obstructions under Quality Housing Zoning often do not
permit adequately sized bulkheads on sites under 125 feet in width. (Bulkheads
are enclosures of stairs to the roof, mechanical spaces and overruns for
elevators). We have identified below the elements of a building that require
rooftop obstructions, as well as specific examples of building designs
compromised by the current New York zoning regulations on bulkheads, and have
proposed alternative zoning text to resolve the potential conflict between efficient
building layouts and appropriate architectural proportions.
The following are examples of rooftop obstructions:
rd
279 Central Park West
355 East 33 Street
211 West 18th Street
East 51 and First Ave
st
Building Elements Requiring Bulkheads
When traction elevators are used – in most mid-rise and all high-rise buildings –
an elevator machine room is required above the elevator shaft. Bulkhead size
does not significantly change with the footprint of a building. Buildings with a
small street frontage have rooftop obstructions similar to those of larger buildings:
bulkheads for two stairs and an elevator and sometimes a water tank. The
current Quality Housing zoning text does not address this fact. This is typically
not an issue in Height Factor regulations because bulkheads are set back from
the front façade of a building and hence do not penetrate the “sky exposure plane.
536LaGuardia Place
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AIA New York Chapter Zoning Study: - Bulkhead Study
Rooftop equipment varies based on building height. Typically, buildings up to 60
feet in height can use a hydraulic elevator, which requires a 12-foot-high rooftop
structure. Buildings over 60 feet in height use a traction elevator, which,
depending on elevator speed, requires about a 20-foot-high rooftop structure,
including the overrun and elevator machine room.
Typically, buildings under 65 feet in height (six stories) do not require a water
tank, using street pressure to provide water for the fire suppression system.
Buildings up to 120 feet tall often do not require a water tank either, using a
booster pump to provide water for the fire suppression system, except when cellar
space is not available, usually due to high bedrock. Buildings over 120 feet in
height often have a water tank; it is typically required for buildings over 300 feet in
height. Tanks are typically placed on top of elevator bulkheads because they need
to be a significant distance above the top sprinkler or plumbing fixture to provide
adequate water pressure. Depending on tank size, the rooftop obstruction
(elevator overrun, machine room and water tank) would require more than 30 feet
in height. The following table gives dimensions for typical rooftop obstructions.
Typical Rooftop Dimensions
Note: All dimensions are approximate
Stair Bulkhead
(Two typically
required)
Scissor Stair
Bulkhead
Elevator Overrun
and Machine
Room
Water Tank
(Varies depending on
building size)
(Per Elevator)
Analysis of Current Zoning Regulations
Zoning Resolution sections 23-62, 24-51, 33-42 and 43-42 limit rooftop
obstructions to 30 feet in width, with an aggregate front-wall surface area of four
times the building frontage. The following excerpts of 23-62 are typical of the
other cited sections:
23-62 Permitted Obstructions
In all Residence Districts, except as provided in Section 23-621 (Permitted
obstructions in certain districts), the following shall not be considered
obstructions and may thus penetrate a maximum height limit or front or rear
sky exposure planes
(d) Elevators or stair bulkhead, roof water tanks or cooling towers
(including enclosures), each having an aggregate width of street walls
equal to not more than 30 feet. However, the product, in square feet,
of the aggregate width of street walls of such obstructions facing each
street frontage, times their average height, in feet, shall not exceed a
figure equal to four times the width, in feet, of the street wall of the
building facing such frontage . . .
The limitation described above penalizes sites in districts with a height limit, and
creates particular difficulties for smaller sites (up to 125 feet in width). Rooftop
structures and equipment include code-mandated stairs, elevator overrun,
elevator machine room, and possibly a water tank, air handling equipment, solar
panels, etc. Attached are five examples of buildings that had to be redesigned to
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AIA New York Chapter Zoning Study: - Bulkhead Study
meet the requirements of the Zoning Resolution, typically at an increased cost
and complication to the building design. On each sheet on the left is the
preferred, non-complying scheme; the image on the right shows how the
bulkhead had to be modified to meet the current regulations.
The Department of City Planning has acknowledged the issue described above in
drafting new zoning text for special districts for the Hudson Yards (93-41, below),
Downtown Brooklyn (101-221), and the West Chelsea District (98-42). In these
districts the text allows a front bulkhead-wall surface area of eight times the
building frontage or 20 percent of the building’s lot coverage and a maximum
height of 40 feet.
93-41 Rooftop Regulations
(a) Permitted obstructions
The provisions of Section 33-42 (Permitted Obstructions) shall apply to all
buildings within the Special Hudson Yards District, except that elevator or
stair bulkheads, roof water tanks, cooling towers or other mechanical
equipment (including enclosures), may penetrate a maximum height limit
provided that either the product, in square feet, of the aggregate width of
street walls of such obstructions facing each street frontage, times their
average height, in feet, shall not exceed a figure equal to eight times the
width, in feet, of the street wall of the building facing such frontage or, the
lot coverage of all such obstructions does not exceed 20 percent of the lot
coverage of the building, and the height of all such obstructions does not
exceed 40 feet…
This is a good solution in zoning districts of R8 and above. In an R6 district,
however, this regulation can permit a 40-foot-tall bulkhead on a building up to 50
feet tall, which the AIA Chapter feels is inappropriate massing, creating a
bulkhead that is out of scale with the height of its building.
Proposed Zoning Text
What is the appropriate massing that will permit necessary rooftop bulkheads and
equipment and yet keep in scale with the size of buildings? Based on an analysis
of permitted building massing using Quality Housing in the R6 through R10
districts, and rooftop equipment requirements, the AIA Chapter recommends that
the following be adopted to address the problems we have described:
[Sec.] 23-62 Permitted Obstructions
***
(d)
Elevator or stair bulkheads, roof water tanks, cooling towers or other
mechanical equipment (including enclosures), provided that:
(1)
(2)
for all buildings, the product, in square feet, of the aggregate
width of street walls of such obstructions facing each street
frontage, times their average height, in feet, shall not exceed a
figure equal to eight times the width, in feet, of the street wall
building facing such frontage,
for buildings 120 feet in height or more, as an alternative to (1)
above, the lot coverage of all such obstructions does not exceed
20 percent of the lot coverage of the building and the height of all
such obstructions does not exceed 40 feet.
All such obstructions shall be no closer than 20 feet to a wide street and
25 feet to a narrow street.
***
[Additionally change Sec. 24-51, 33-42 and Sec. 43-42 to read the same]
The current requirements are also an impediment to the installation of solar
panels and other rooftop energy conservation/co-generation devices, since these
types of mechanical equipment are currently not even permitted as obstructions in
the general requirements of the Zoning Resolution. (They are so permitted under
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AIA New York Chapter Zoning Study: - Bulkhead Study
the revised standards the City Planning Commission is using in its new special
districts which list a generalized “other mechanical equipment” as a permitted
obstruction. No such category exists in the general provision.) Certainly, solar
panels consume an overwhelming share of the allotment for permitted
obstructions and thus might be rejected because of this issue, an unfortunate
consequence. We recommend making them a permitted obstruction as has been
the case in new special districts.
The attached diagrams summarize the R6, R7 and R8 Quality Housing bulk
regulations, assuming a 50-foot wide site. The diagrams illustrate a rooftop
obstruction envelope of 400 square feet for buildings under 120 feet in height, and
a rooftop obstruction of 40 feet in height for buildings 120 feet and greater in
height (R7X; R8-wide street, outside Core; R8A; R8X), generally documenting the
problem we are raising.
Subm A. Radzicki, M. Ginsberg & M Parley
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