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<br />DECEMBER 2000
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<br />PLAtJNIiJG
<br />ASSOCIATION
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<br />By Jim Schwab, AICP
<br />ecember may not always be the coldest month, but it is rhe
<br />darkest, and the darkness is moze pervasive the Eurther
<br />north one goes. In this season of short days and long shadows,
<br />Zoning Neuis offers a brief overview of regu(atory attemprs to
<br />make the urban winter more livable by controlling the height
<br />and buik of buildings. These controls let adequace sunlight
<br />reach public spaces and help to ceduce wind acceleration.
<br />Skyscrapers often have besn built with
<br />lifitle regard For the liice(y affect an the
<br />external urban climate
<br />����eea� ���������� �� ������ ���sa��
<br />The idea of achieving greater human corzzfort through urban and
<br />architectival design dates to the beginning of civilization.
<br />Archaeolagists have long noted the variety of human adaptations to
<br />l'unatic circucnstarzces. Ancient civilizatians often used narrow
<br />,assageways between buildings to provide shade and protection
<br />from the hot sun. In colder climates, rhe wind-inducing, shadow-
<br />producing effects of taller buildings azose as a concern only after
<br />advances in building technoiogy permitted the erection of such
<br />structures, Prior to rhe Indus�rial Revolution, commeccial and
<br />industrial interests found litrle utility in huge buildings—the callest
<br />building in zz�ost norrhern cit�es was a cathedral. Tn rhe twentieth
<br />century, however, sicyscrapers often have been buik with little
<br />zegard Eor the li[�efy afFecc on the ex�ernal urban climate, even as
<br />technology has allowed us to aclueve neazly complete control of the
<br />indoor climate.
<br />Even sa, as Marc A. Weiss notes (see "Skyscraper Zonittg,"
<br />,%urnal of the 14merican PlanningAssociatian, 5pring 1992), from
<br />the� 1890s on, che increasing density of modern city cenrers
<br />spurred zonit�g efforts to regulate the height and bullc of tall
<br />buildings, particula�ly in Nev✓ York City, where access to light
<br />and air surfaced early as a primary concern. These issnes also
<br />helped spur regulation of the design of the ciry's residentia[
<br />tenements. In Manhattan's commercial districts, the new
<br />regulations tziggered a wave of commercza( design that
<br />emphasized the use of setbacics to scep back the bulk of
<br />buildings at higher elevations, allowing adequate sunlighr to
<br />zeach Iower levels and �he street. This "wedding-cake" design
<br />was one of the primary features of the Empire Srate Building in
<br />1931, which, despite its elevacion, met the ciry's height and
<br />bulk regulations,
<br />Tn more recent years, pioneezing microciimate smdies have
<br />prompted a new wave o£ building regulations by examining in
<br />detai( the impacr of ta11 buildings on shading, sunlight, and
<br />wind speed in downtown streeES and parks. To a lesser extent,
<br />issues of solar access for neigfiboring buildings also have
<br />motivated some oE these technical studies. These issues affect
<br />suburbs and smaller cities as well as Iarge city central business
<br />districts because they touch rhe essence of conteactual zoning:
<br />Wfiat is tolerabte in a dense downtown may be very differenc
<br />fzom what is tolerable in a less dense residential or
<br />neighborhood commercial area. �
<br />One Final note is also in order. Most older cities have an
<br />abundance oF tall buildings developed under standards (or even
<br />without standards) that predare current zoning regulations.
<br />Inevitably, these affect the degzee of sunlight reaching streets,
<br />parks, or surrounding properties in ways that vary from current
<br />or proposed guidelines, and for which they must be accounted.
<br />for, Zoning codes that seek to pzotect sunlight for opea areas in
<br />densely buift neighborhoods generally malce some allowance for
<br />new buildings whose projected shadows mezely overlay rhose oF
<br />eristing structures so as not to penalize new development
<br />unnecessarily, while also preventing or mitigating new
<br />encroachments where possible.
<br />Pioneering microclimate rtudies have prompted a
<br />new wave ofbuilding regulutionr by exctnaining in
<br />detail the impact of tdll buildings, surb as Citicorp
<br />Center, on shading, sunlight, and wind .rpeed in
<br />downtown .rtreetr and park.c.
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