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REAL ESTATE
AND
NEW YORK, FEBRUARY 3, 1917
FEATURES OF SKYSCRAPER CONSTRUCTION
UNDER THE ZONE RESOLUTI.ON
â– \Y/E are on the verge of a new era in
•^ tlie design of tall buildings in New
York. The ne.\t few years will be
marked in the city's building history as
those which saw the establishment of a
new skyscraper architecture. The intro¬
duction of structural steel and the caisson
foundation has been potent in revolu¬
tionizing the appearance of Manhattan's
buildings, but the curb, which in the in¬
terest of better light and ventilation, the
Board of Estimate has lately put upon
the heights made possible by these sys¬
tems, will effect equally great changes in
the appearance of new skyscrapers.
The restrictions placed upon the height
of buildings and the sizes of yards and
courts by the Resolution, commonly
known as the Zone Law, adopted by the
Board of Estimate on July 25, 1916, vary
in different parts of the city, but the only
ones we need consider as having an im¬
portant bearing upon future large struc¬
tures are those that prevail in Manhattan
south of 59th street.
In this section we find the "Two and
One-half-times District," the "Two-times
District" and the "One and One-half-
times District," each of which designates
in multiples of the street width the
height to which a wall may rise upon the
street line. It will be sufficient to con¬
sider in detail the requirements of the
"One and One-half-times District," as
they are identical with the others in prin¬
ciple and more stringent in specification.
The corresponding "Area Districts,"
the requirements of which regulate the
sizes of yards and courts, are the "A Dis¬
trict" and the "B District." The "A Dis¬
trict" is that covering the warehouse and
industrial areas and is the most lenient
in its requirements. The "B District"
covers most of Manhattan and specifical¬
ly the sections in which we may expect
the erection of future notable buildings.
As, ill addition, it applies similarly to the
various "Height Districts," it may be
considered jointly with the "One and
One-half-times District."
The "One and One-half Times" (one
and one-half times the street width)
height limit will not impose any greater
restrictions upon tenement houses than is
now imposed by the Tenement House
Law except upon streets exceeding one
hundred feet in width. The "B District."
moreover, is no more stringent than is
the combination of Tenement House Law
and Building Code requirements enforce¬
able in the construction of tenement
houses. We may thercfbre eliminate
them from further consideration and de¬
vote our attention to non-tenements.
Of these, the simplest type that inay
possibly be erected to a height exceeding
one hundred and fifty feet is the loft
building without dividing partitions and,
therefore, easily lighted without the ne¬
cessity for intricate courts or yards.
Aside from the set-back requirements,
the only new point introduced by the
Zone Law is the necessity of providing
a yard space behind buildings on certain
interior lots and the limiting specifica¬
tions for the length of outer courts and
for the size of inner courts.
Other prospective big buildings will fall
into either the office building class or into
the hotel class, in each of which the sim¬
plicity of the loft type will be lost. New
problems will be induced by the neces¬
sity of lighting all living rooms and the
necessary introduction of open spaces or
By FRANCIS P. SCHIAVONE
courts into the heart of the building.
Thus a more complicated floor plan is
required and the most economical layout
of a given plot more difficult to find. In¬
stead of there being, as heretofore, per¬
haps, one typical floor plan, there will be
several, as the height rule neces.sjtates
set-backs of the the street w-alls and the
yard and court rules require progressive
increases in the width of open spaces.
The theory of the height limit rules
of the Zone Law is the same as that
which forms the basis of the court rules
of both the Building Code and the Zone
Law. The requirements are designed to
maintain a predetermined "angle of
li,ght" or "sky angle" for all heights of
building. They establish inclined planes
beyond or above which no part of a
structure may project. So long as these
planes are not pierced, there is no
height limit.
In applying this theory to the limita¬
tion of the walls upon the street line, in
the "One and . One-half-times District."
the limiting plane (or planes) is a verti¬
cal production of the street line to a
height of one and one-half times the
street width and is thereafter inclined
away from the center of the street in
the ratio of one horizontally to three
vertically. These planes arc related to
the street rather than to the space be¬
tween streets and are to be maintained
inviolate on all sides of blocks irrespec¬
tive of property subdivisions or the
identity of buildings to the end that no
building shall project beyond the limit¬
ing plane for any street whether it faces
on that street or on another street or on
no street at all.
This principle applied by the Building
Code to courts, erects opposite vertical
planes forty-eight feet high and four
feet apart and other planes inclined
thence apart in the ratio of one hori¬
zontally to every twelve vertically. An
inner court is limited by four such
planes, an outer court by two.
The Zone Lavv modifies this in the
"B District" by specifying certain mini¬
ma for yards and outer courts and a
ratio of one to six for the inclined planes
of yards. It imposes also a somewhat
complicated limit upon inner courts, a
requirement consisting of an area mini¬
mum and a correlative width minimum.
A sharp distinction should be drawn
between the yard required by the Zone
Law and all other open spaces. The pro¬
vision of a yard is in certain cases com¬
pulsory and in such cases it is required
to be of a certain size. All other open
spaces are not required to be provided,
but if included in the plan must equal
or exceed a certain minimum. The yard
is required primarily for block lighting
and ventilation irrespective of its utiliza¬
tion by the building on the same lot.
Other open spaces, if provided, are de¬
signed exclusively for the building on
the same lot.
The yard, being required, must begin,
for lots on residence streets—-not above
the curb level and on business and un¬
restricted streets—not above the second
tier of beams or in any case above a
point twenty-three feet above curb
level. Other open spaces may begin at
any level they are needed.
It may confidently Jbe stated that prac¬
tically all large buildings will be built,
as heretofore, on corners or large plots
including corners. This the Zone Law
encourages by exempting corner lots
from the necessity of providing a yard
irrespective of the character of the block
plan. Likewise a corner may be any
size; may include one corner, two, three
or a whole block.
Interior lots will, under certain cir¬
cumstances, have to have yards. Build¬
ings running through trom street to
street may have to provide open spaces
on either side in lieu of yards. Each
of these is required to be at least of the
area of an inner court, the width of an
outer court and to start not higher than
twenty-three feet above the curb.
As yards in the "B District" must be
at the bottom at least ten per cent, of
the lot length and increase above that
depth in the ratio of two inches in depth
for every foot of height, it is evident that
the question of whether a yard is re¬
quired or not and its size are all-impor¬
tant.
It must be remembered that the set¬
backs on the street line and the sizes of
yards and courts are all factors of the
height; that is, that the open spaces
whether in street, yard, outer court or
inner court must increase in width as
the height increases. In the design of
a building bulk, therefore, that will best
suit certain requirements, the factors of
net-cubage, width of pavilions, character
of open spaces and height of buildin.g
are all very closely interrelated. No one
may be altered without in most cases
drastically affecting some or all of the
others. Within certain limits the height
of the building must be known before
the court spaces may be determined
upon. The minimum and maximum
w'idth of pavilions—varying with the
character of the building and size of
rooms—will place a limit on the dispo¬
sition of open spaces; the height of the
open spaces will be as potent a factor
and will be more important perhaps in
determining whether these open spaces
shall be inner or outer courts.
Where land and Jloor space are ex¬
tremely valuable there will be set-backs
in court and yard walls, but where the
space thus, to be saved is not worth the
cost of the set-backs, the court walls will
be unbroken in their vertical sections.
A selected motif of design may require
that there be many small set-backs in
the exterior walls or the mansard may
be used, but otherwise there will usually
be not over two set-backs below the
tower, which, under the Zone Law, is
exempt from the height limitations so
long as it is a certain variable distance
back from the center of the street.
The requirements of design will not
be so important in courts and the only
reason for set-backs in the walls of such
open spaces will be the utilization within
the building of all available space and
perhaps the' lighting of various floors
by means of skylights set in the roofs
or decks of the set-backs.
The necessity for set-backs on the
street wall, and in many cases on court
walls, will mean the almost exclusive use
of the skeleton frame. In tall buildings
on narrow streets it is probable that
though the central portion will be skele¬
ton (with walls supported at every floor)
the exterior portion of the building above
which the rest sets back will be curtain-
wall construction. On wide streets and
where the height limit is two or two and
one-half times the street width, the street
skeleton will most probably be used
throughout.