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Abstract and Figures

Increasing urban density leads to a conflict between space-use efficiency and daylight access. Cities have traditionally relied on zoning guidelines that consist of section-based geometric evaluation techniques and/or hours of access to direct sunlight. However, it is now possible to quantify the performance of detailed design proposals before construction. Annual climate-based daylighting performance metrics for urban environments can be computed accurately, in high spatial resolution and in a timely manner. Given that massing design decisions at the urban planning level may make or break the long-term daylighting potential of a whole neighbourhood, the adoption of these tools by zoning boards, developers and urban planners seems particularly relevant. A simulation-based daylighting analysis procedure reveals the capabilities for both formulating more nuanced prescriptive zoning rules as well as for use by design teams. The procedure is used to evaluate the daylighting performance of 50 block typologies in New York City (NYC). The analysis demonstrates that certain urban massing approaches (e.g. pencil towers on a contextual base) outperform conventional massing strategies. A second case study application of an actual city block shows that innovative urban massings can improve access to daylight for the massing itself as well as for neighbouring buildings.
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Daylit Density A simulation-based framework for the development of
urban zoning rules for daylighting
Emmanouil Saratsis, Timur Dogan, Christoph Reinhart
Sustainable Design Lab, Massachusetts Institute of Technology, Cambridge MA 20138, USA
ABSTRACT
Population growth and related space constraints have led to a planning paradigm that promotes
living and working in high-density urban areas. Increasing urban density, however, leads to a
conflict between space-use efficiency and access to daylight. To manage this conflict and to
e
nsure sufficient solar access, cities have traditionally relied on zoning guidelines that propose
simple, two-dimensional geometric evaluation techniques. This practice seems antiquated in
times when computer aided design tools enable architects to test designs before construction.
Recent advances in building performance simulation software allow us to compute annual
climate-based daylight performance metrics of urban environments accurately, in high spatial
reso
lution and in a timely manner. Given that zoning requirements as well as massing design
decisions at the urban planning level may make or break the long-term daylighting potential of a
whole neighborhood, the adoption of these tools by zoning boards and planners seems
particularly relevant. This manuscript therefore presents a simulation-based framework for
formulating more nuanced prescriptive zoning rules, along with a performance-based approach
for de
velopers and planners interested in exploring innovative urban massing solutions. The
framework is used to evaluate the daylighting performance of common and innovative urban block
typologies in New York City. The performance of the investigated massing designs varies; in some
cases the designs significantly outperform existing strategies, supporting urban densities that are
twice as high as current zoning maxima. Findings are illustrated using a case study and compiled
Draft
into a set of recommendations for zoning boards, planners and real estate developers towards
more sustainable management of solar access at the urban scale.
Author Keywords
Urban planning; urban daylight simulations; daylight availability; performance-based zoning;
INTRODUCTION
Urbanization and urban densification are ubiquitous trends worldwide [15]. In established US
urban centers, increasing densities are widely observed; from downtown redevelopment
schemes, to
infill projects in lower density areas as well as the densification of de-industrialized
zones. The rationale for increasing density ranges from higher economic profitability to enhanced
urban-scale sustainability by preserving land and resources, minimizing transportation footprint,
and fostering socially cohesive urban communities [8]. A frequently-asked question is, apart from
the parameters that justify density, what should limit it? It has been argued that conte
xtual values
such as historic patterns and social ties form part of the equation. Yet, equally crucial and
recognized aspects are human well-being and the preservation of access to natural resources
such as air and light both within buildings and at street level.
It seems self-evident that urban geometries have a significant impact on individual buildings’
access to natural light. Street orientation and width, surrounding building heights, and urban
canyon characteristics all contr
ibute to the amount of direct sunlight and diffuse daylight that a
building facade receives. Given that these variables are unlikely to ever change, a site’s maximum
build-able volume, prescribed in a city’s zoning ordinances, effectively determines the daylighting
potential of all buildings in the affected jurisdiction in perpetuity. While architectural modifications
to floor plans and sections, material choices and facade manipulations can either exploit this
dayl
ighting potential or choose to ignore it, the maximum possible daylight performance level of
Draft
a neighborhood is decided upon at the zoning stage. How well do current zoning ordinances
preserve access to daylight?
Across the world, the conflict between urban densification pressures and daylight access, has
been addressed by cities through zoning resolutions. These resolutions usually propose simple,
two-dimensional geometric evaluation techniques to ensure fair solar access to all buildings and
streets. Although these resolutions are grounded in environmental concerns, they often seem
rigid, inflexible and even at odds with a city’s development potential. Recently, developers in
Manhattan and elsewhere have come up with creative ways to increase density. New prototypes
with smaller footprints, increased environmental performance and sensitivity towards the
established historical fabric have been presented in an effort to convince zoning boards to build
higher, while limiting contextual impact. For example, a skyscraper proposal for West 57th street
recently approved by the NYC Landmark and Preservation Commission, features a contextual
base that respects the architectural character of adjacent building facades, and a slender glass
tower that rises to become one of the tallest structures in the United States. At the same time,
citizen groups have been protesting new high-rise construction projects in the area [19], claiming
they would ‘cast mile-long shadows over Central Park’, a celebrated public amenity. It becomes
apparent that controlling density in a highly desirable urban context can easily lead to conflict
among different stakeholders. In order to productively contribute to such urban disputes, this
research seeks to discover the equilibrium point for economically profitable, yet environmentally
fair urban densification.
As an example, the framework is applied to New York City, an iconic center for both urban
dwellers and developers. The city has been receiving high-density development pressures ever
since the dawn of the 20th century. In fact, New York was the first city to implement solar access-
inspired zoning laws as early as 1916. Since then, its zoning resolutions have been used as model
manuscripts for cities around the world, while, internally, the ‘rights to natural resources’ have
sparked a continuing passionate debate among developers and involved citizens. In the following
section, in order to appropriately discuss this topic, we will present a short summary of the existing
zoning framework as documented in the New York City Zoning Handbook [7].
New York City’s Zoning Guidelines today are an evolution of the original document from 1916.
Over the years, changes were introduced that reflected different schools of thought in urban
planning. The original 1916 Zoning Resolution was provoked by the Equitable Insurance Building
in Lower Manhattan. The intense overshadowing problem that this building caused, combined
with imminent pressures for new housing development, triggered the creation of a then radical
document that established height and setback controls and that served as a model for urban
communities across the United States facing similar challenges. The next major Resolution was
introduced in 1960, with a clear imprint of Le Corbusier’s ‘towers-in-the-park’ approach,
advocating for vast open space on the ground level and vertical concentration of density in
sparsely located towers. The resolution incorporated the concept of ‘incentive zoning’, trading
additional floor area for public amenities. Over time, urban theories institutionalized by the 1960
Zoning Resolution fell out of favor and were instead viewed as counterproductive to the city’s
vitality because they were disrupting the continuity of the streetscape. Recent revisions of the
New York City Zoning Resolution, have hence aimed to offer a more responsive and sensitive
approach to planning by encouraging mixed use development, protecting the character of
historical neighborhoods, and broadening inclusionary zoning incentives for affordable housing.
The Zoning Handbook organizes New York’s metropolitan region into Zoning Districts, each with
its own land use groups and sets of metrics governing maximum building envelope form, open
space and parking requirements. It establishes district-specific regulations and provides
illustrations of typical building forms that would be generated by them. In an ‘as-of-right’
development scenario, high-density zoning guidelines prescribe:
Tower-on-a-base typology;
This frequently proposed typology is vertically organized into two volumes with distinct formal
properties: the contextual base, that rises to a prescribed ‘base height’ continuously following
the street line, and the tower, that is set back from the street line and is required to have a
large percentage of its floor area below a prescribed ‘tower height’.
Building envelopes defined by the sky exposure plane;
A sky exposure plane is defined as ‘a virtual sloping plane that begins at a specified height
and rises inward over the zoning lot at a ratio of vertical to horizontal set forth in district
regulations’. It is prescribed to provide light and air at street level.
Building height and setbacks defined by street width;
Two thresholds for street are defined: a narrow street (less than 75’ wide), and a wide street
(more than 75’ wide). Based on the definition of the street, the buildings are required to have
a 10’ or 15’ setback beyond the ‘base height’. The maximum building height is also frequently
defined by the distance of the building from a wide street.
Floor area increases justified by provision of open space;
In certain settings, the provision of an ‘urban plaza’, an ‘open area for public use adjacent to
a non-residential or predominantly non-residential building’, allows developers to increase the
floor area of the building up to 20%. This area has to be unobstructed from its lowest level to
the sky.
The zoning guidelines also include case-specific regulations for special projects that don’t
conform to the ‘as-of-right’ category. The developers of these projects are usually asked to
present overshadowing studies to the zoning boards, in order to prove that they don’t significantly
limit solar access of surrounding properties.
This manuscript argues that the above described regulations of the NYC Zoning Board have a
number of limitations. First, daylight access is presented as a concept tied to the streetscape. The
constant densification of the city is eventually going to limit the daylighting potential not only on
the street, but also for the interiors of buildings; the need arises to respond to this challenge as
well. Second, although the district definition is detailed, form-generation guidelines for buildings
largely remain decontextualized from the building’s particular surrounding. Current guidelines
therefore have only limited means to adequately ensure fair access to daylight in more spatially
complex conditions. Third, the zoning rules are climate- and orientation- agnostic, ignoring the
amount of daylight that is available for different facades over the year. Fourth and foremost,
despite a growing consensus on how to evaluate the daylight availability in a building, current
guidelines do not specify the actually required daylighting performance for proposed urban
geometries. This manuscript therefore applies the latest generation of building-level daylight
availability metrics at the urban scale.
Before reviewing these daylighting metrics, several previous studies concerned with
daylighting access in neighborhoods are being reviewed.
Compagnon [2] proposed a workflow to evaluate the daylight potential of buildings by
obtaining irradiance values on building facades in order to compile thresholds that could identify
‘good’ designs. Although this approach is a good starting point, it neglects that daylight availability
is highly dependent on building depth.
In later research, Strømann-Andersen et al. [14] accounted for building depth by analyzing
typical street canyons in section. Their research examined the relationship between building-
scale, passive energy factors and urban density and established the interrelation between urban
geometry and building operational energy. This mostly 2D approach is however only applicable
to urban settings that are homogeneous in height and that are predominantly consisting of street
sections that can be approximated as infinite extrusions. For high-density environments with tower
typologies this methodology can’t be applied.
Cheng et al. [1] introduced a three-dimensional approach to examine the relationship
between density and daylight availability. By cross-referencing daylight factors and plot ratio, their
research aimed to identify performance trends and to relate them to geometric attributes of
models. This study revealed the potential of daylighting simulations for urban design decision-
making. However, it has to date only been applied to a very limited set of urban models and the
daylight factor, that was used by the authors, is not a climate-based metric.
Climate-based daylighting metrics have been investigated and promoted by several groups for a
number of years. Over the past decade several research groups have promoted the so-called
climate based daylighting metrics that are based on annual series of hourly indoor illuminance
calculations [6; 12]. In 2012 the Illuminating Engineering Society of North American (IESNA)
introduced Lighting Measurement protocol LM-83, that recommends the use of spatial daylight
autonomy metric, sDA, to evaluate the daylight availability in architectural spaces [4]. According
to the LM-83, a point in a building can be considered to be “daylit” if at least half of the occupied
time (50%) the work plane illuminance at the point due to daylight is above 300lux (sDA
[300lux][50%]
).
In 2014 the US Green Building Council’s adopted a version of LM83 for it’s the daylighting credits
in its LEED v4 green building rating system [17]. The sDA
[300lux] [50%]
target level for a space
according to LEED v4 I is 55% of regularly occupied floor area.
In order to calculate spatial daylight autonomy distribution at the building levels, practitioner have
traditionally relied on daylight coefficient based methods such as Radiance/DAYSIM. Radiance
is a validated backward ray-tracer developed by Greg Ward at Lawrence Berkeley National
Laboratory [18]. DAYSIM is a Radiance-based annual daylight simulation program that effectively
predicts hourly time series of interior or façade illuminances [11].
A barrier towards to use of a simulation tool such as DAYSIM for urban level analysis is the time
required for model setup and simulation. Dogan et al. [3] therefore introduced a novel method
called ‘Urban Daylight’. In order to speed up the interior illuminance calculation for urban level
simulations, where interior floor plans and partitions are anyhow unknown, Urban Daylight uses
DAYSIM to calculate hourly illuminance levels on discrete facade patches. An impulse-response
method is then used to convert outside illumination levels into diffuse light propagation in the
interior of a building. The sum of all façade impulses add up to hourly illuminance profiles across
a floor-plate.
Building on this research, the authors present a consistent workflow to evaluate daylight
performance of urban massing models. The relationship of density and daylight availability is
quantified in accordance with the above mentioned IESNA LM83 / LEED v4 criterion sDA
[300lux]
[50%]
. The workflow is applied to 50 urban-scale massing examples and a set of recommendations
for performance-based zoning is derived. The workflow may serve two purposes: Municipalities
may use it to derive evidence-based, prescriptive daylight zoning laws for their jurisdiction while
designers and developers are presented with a performance-based framework within which they
can propose innovative massing concepts without compromising access to daylight.
METHODOLOGY
The research that can be divided into two steps, test case generation and simulation-based
evaluation.
Test case generation and growing scheme
Modeling a neighborhood is a complex task. Among the first parameters that need to be defined
is the spatial size and resolution of the test geometry. This choice is complicated because zoning
and planning processes transcend multiple scales, from specific building envelopes to general
zoning districts. This means that while the model has to be seen at the urban scale, the actual
evaluation of local daylighting conditions require geometric detail down to the window and
individual floor scale. Given these two requirements, the authors decided to work at the resolution
of the urban block as an intermediate scale bridging the gap between buildings and districts.
Block dimensions were 140m (450’) by 60m (200’) in line with typical dimensions of a high-density
block in New York City [Table 1].
Table 1. Geometric parameter values
Parameter
Value
Block Length
140m (450’)
Block Width
60m (200’)
Layer A (Base) Height Range
3-6 levels (9-18m)
Layer B (Tower) Height Range
1-50 levels (3-150m)
Five specific block typologies, which are frequently found throughout the city, were picked with
diverse footprint types and levels of permeability at the ground level [perimeter, atrium, courtyard,
alley, double alley]. Each typology was then subdivided into two geometric layers with distinctive
characteristics [Figure 1]:
Figure 1. Block typology diagram
Layer A. The base layer; the geometric expression of the ‘contextual base’ as defined in the
NYC Zoning Resolution, it follows the ‘street line’ and defines the street wall’.
Layer B. The towers layer; the geometric expression of the ‘towers’ as defined in the NYC
Zoning Resolution, they rise on top of the base and are completely contained within its footprint.
In order to work within a larger urban context, it was assumed that the investigated block would
repeat itself across a neighborhood, meaning that the block typology under investigation was
assumed to be surrounded by identical blocks leading to 3 by 3 block sized urban simulation
models (Figure 2). The choice to surround each block with its own kind was made to avoid an
‘export of problems’ outside of the simulated area of interest e.g. by building sets of high rises in
a low-rise context. The street width was set to 20m (65’). Block orientation reflects New York
City’s condition, with the short dimension aligned with the north-south axis.
Figure 2. Simulation Context Diagram
A growing scheme was then developed to produce a variety of densities for each typology, while
maintaining its essential formal characteristics. To quantify density, the authors used the zoning
metric floor-area ratio (FAR), prescribed in the New York Zoning Handbook as ‘the principal bulk
regulation controlling sizes of urban geometries. FAR is defined as the ratio of total building floor
area to the area of its zoning lot. The reference zoning lot area was the city block. Ten variants
were then generated for each typology ranging from an FAR of 2.0 to 30.0 (Figure 3).
In order to emulate a realistic growing scenario there is a distinction between the base layer and
the towers layer, each altered separately, as described in Table 1. This is a frequently observed
scenario in New York City, where the base layer is usually made of a continuous array of buildings
fronting the street with a consistent height of 3-6 levels, while the towers rise as slender volumes
at different heights.
Figure 3. Block typology evolution matrix
Simulation setup
The daylight performance potential of the previously described 5 x 10 cases in the New York
climate was simulated using ‘Urban Daylight’ [4]. Based on hourly illuminance profiles, the
program calculates the spatial daylight autonomy sDA
[300lux] [50%]
for each floor plate. Since this
study is focused on the maximum daylight performance potential of a neighborhood, a window-
to-wall ratio of 100% and glazing with a visible transmittance of T
vis
50% was applied. The Urban
Daylight light transport mechanism form the façade into interior spaces relies on a diffuse
distribution and hence models the equivalent of a 100% diffusing glass with T
vis
50%. The IESNA
sDA specification also includes blind operations and prescribes to trigger blinds when 2% of the
room area is exposed to direct sunlight. Due to limitations in the control mechanisms in Urban
Daylight, the authors approximated the IESNA sDA specification with blinds with a 50% cut-off
value that are triggered at 20,000lux or higher on the façade. The blinds operate independently
on discrete façade patches with a width of 40cm. The floor-floor distance is set to an average of
3m. A detailed list of simulation parameters can be found in Table 2. Each of the urban block
prototypes is simulated within a generalized context. The floor-floor distance is set to an average
of 3m. A detailed list of simulation parameters can be found in Table 2. Each of the urban block
prototypes is simulated within a generalized context.
Table 2. Simulation parameters
Parameter
Setting
Ambient Bounces (AB)
4
Ambient Divisions (AD)
1024
Ambient Super-Samples (AS)
512
Ambient Resolution (AR)
256
Ambient Accuracy (AA)
0.2
Occupancy Hours
8AM 6PM
Sampling Distance Inside
0.5m
Blind trigger point
20,000lux
Façade window to wall ratio
100%
Glazing type
T
vis
50%, 100% diffuse
RESULTS
Figure 4 presents a visualization matrix showing urban block density evolution with individual floor
plates false-colored based on daylight availability levels. Predictably, the figure reveals a steady
decline in daylight availability for the lower floors of the typologies as the density increases.
Another common characteristic are good daylighting levels at the top floors of the towers across
all typologies. The different color patterns for each block solution reflect the unique geometric
features of each case.
Figure 4. Block typology evolution matrix with daylight availability mapped on floor plates
Figure 5 shows overall sDA
[300lux] [50%]
values as a function of FAR for all typologies. Different
variations of the same typology are connected with colored curves. For further reference, the
maximum allowable current FAR is plotted along with the LEED version 4.0 daylighting credit
requirement. The latter is an approximation since it assumes that all areas across all floor plates
are regularly occupied spaces which might not be true since the floor plates will necessarily
include core and circulation spaces. As mentioned above, the use of blinds is also being
neglected. Working with these assumptions, only Typology A meets the LEED requirement for
FARs up to 12.
Figure 5. Spatial daylight autonomy vs. Floor area ratio graph
In order to better understand what these results might imply for a developer, Figure 6 plots
absolute daylit area sizes based on sDA
[300lux] [50%]
for the five highest densities for each typology
against floor area ratios. Assuming in this case that only the outer zones (5 m distance) along the
building façade areas count as “regularly occupied spaces” according to LEED, the gray dashed
line represents the LEED v4 sDA
[300lux] [50%]
55% threshold line. Assuming a zoning law that follows
LEED v4, typologies lying above the gray line “daylit” or LEED v4. Typology B never meets the
criterion. The maximum compliant variants for Typologies D, E and C are 3.5, 5.5 and 9.5,
respectively, i.e. they are below the current maximum NYC FAR of 12. Typology A on the other
hand tops out at an FAR of 24.1.
While Figure 5 demonstrates interesting relationships between urban density and overall daylit
areas in various urban typologies, it does not reveal how even the daylight is distributed across
the floor plates within each typology. As evident in Figure 4, lower floor plates tend to be worse
daylighting performers in dense arrangements. Figure 6, therefore, shows how sDA
[300lux] [50%]
results are distributed among different floor plates. Variant B10 has 7 floor plates with an sDA
[300lux]
[50%]
value above 90% versus 78 with a value below 10%, showing a strong daylighting imbalance
across the typology. This indicates that zoning boards should specifically focus on the solar
access of the lowest floors and the streetscape. Figure 6 also shows that the floor plates towards
the lowest end of the performance spectrum tend to have a significantly negative impact on
cumulative typology performance. Variant C8, for example, has 73 floor plates with an sDA
[300lux]
[50%]
value above 90% versus only 14 with a value below 10%; they are, however, enough to drive
its cumulative score down to 40%. This can be attributed to the fact that the lowest bin floor plates
tend to be the ones with the largest area and the least exposure to daylight, usually making up
the base layer. Such findings suggest the introduction of additional zoning regulations that ensure
daylight penetration in deeper floor plates.
Figure 6. Matrix of floor plate performance histograms
DISCUSSION
The previous section has shown that different urban typologies may have dramatically different
daylighting performance according to the earlier presented LEED v4 based neighborhood
evaluation framework. What are the implications of this finding for zoning boards, planners, real
estate developers and architects?
Urban-scale daylight availability standards
Daylight access at the building scale has proven benefits for occupant health, visual comfort,
aesthetics and operational energy use [10]. In order to ensure this access during design, LM-
84/LEED v4 promote an effective, new set of daylight availability metrics. As the same time, the
recent partnership of the Congress for the New Urbanism (CNU) with the United States Green
Building Council (USGBC) and the National Resource Defense Council (NRDC) to propose LEED
for Neighborhood Development (LEED-ND), a ‘system for rating and certifying green
neighborhood development’ [16] illustrates a growing desire to also systematically assess
sustainability criteria such as daylighting at the urban scale. The LEED-ND 2009 standard,
however, does not include guidelines for daylighting, probably because the calculation of sDA at
the urban levels used to be to time and resource intensive to request. With the expansion of sDA
calculations to the neighborhood level as presented above, a new workflow is now available that
could be adopted by future version of LEED-ND.
A remaining question is what the minimum urban sDA
[300lux] [50%]
requirement for such a standard
should be. Figure 5 suggests that 55% minimum requirement is high since most of the evaluated
typologies crossed it at low FARs of 4.0 to 8.0. This finding can be attributed to the fact that the
LEED v4 standard applies this criterion to regularly occupied areas only, while the presented
evaluation takes the entirety of the floor area of the block into account. At a later design stage the
area could of course be broken into circulation and regularly occupied areas but during early
massing design this level of architectural specificity is not available. Figure 5 suggests that a more
reasonable requirement for urban planning studies is to require an overall sDA
[300lux][50%]
between
45% to 50%, since the sharpest performance drop for most typologies occurs around those levels.
Such a threshold would allow for increased FARs and hence profitability as described in Figures
7 and 8, respectively: Assuming a value of $11,720 per square meter based on the Douglas
Elliman report for condominium residential units in Midtown Manhattan in 2010 [9], Typology A
reaches a value gain for a developer over current admissible built volume of $1.14 billion per
block.
Figure 7. Spatial daylight autonomy vs. Floor area ratio graph with proposed threshold
Figure 6 indicates that it is insufficient to simply aim for averaged scores at the urban-scale and
that it is instead advisable to also establish a lower bound for per floor plate performance scores
to ensure that the lower floors will not fall below a certain threshold as densities increase. This
could also be an indirect way of accounting for daylighting quality on the streetscape, a major
public health debate point and an indispensable asset for a city’s vitality.
Figure 8.Daylit area vs. Floor area ratio graph
Zoning and urban development processes
As mentioned before, the LEED v4 simulation based zoning framework can be used in two
manners by both local zoning boards and urban designers:
Prescriptive zoning
By evaluating the plotted curves of Figure 5 a zoning board can identify FAR ranges until
which compliance with a set daylight availability limit can typically be maintained. Beyond this
threshold, small increases in density tend to result in significant decreases in daylighting
performance. Finding this threshold could help zoning boards to formulate evidence-based,
geometry-sensitive and climate-specific FAR limits for prescriptive zoning laws.
Performance-based zoning
Figure 6 further shows that some typologies have a wide densification margin at high
daylighting performance levels. This means that whereas certain massing schemes reach
their densification limit early on, others display higher potential for added area, meaning higher
profitability rates for developers at a sustainable environmental cost. By using an alternative,
performance-based compliance path to the zoning laws outlined above, developers could
hence explore and further develop high performance design solutions. This approach would
free them from the rigidity of traditional planning regulations and propose denser design
schemes, provided that they meet prescribed performance criteria.
Design workflow optimization
Even though this workflow is presented within the context of the zoning process, it can also be
applied at the architectural design level, assisting designers with creating code-compliant designs.
Through conciliating two usually independent space planning processes, it could reveal new
opportunities for design and enhance architects’ and developers’ understanding of the contextual
impact of their proposals. Another interesting venue for designers would be to optimize space-
use distributions within buildings based on daylight availability requirements for different types of
programmatic functions (residential, commercial). The possibility of accurately mapping
daylighting potential on the floor plate, could create interesting precedents for floor-plan design
decisions, such as circulation planning, number of internal subdivisions, or room depth.
Case Study: C64X Zoning District, New York City
In order to contextualize the impact of the research findings for New York’s Zoning Regulations, the authors
chose to demonstrate the suggested workflow on one of the city’s highest density zoning districts, coded
C6-4X. According to the Regulations, C6 districts permit a wide range of high-bulk commercial uses
requiring a central location, specifically corporate headquarters, large hotels, entertainment facilities, retail
stores and high-rise residences in mixed buildings. The maximum FAR permissible in these districts is 10.0
to 15.0 under special conditions, accommodated in tower-on-a-base typologies, with a maximum height of
35 stories. [7]
For the purpose of this analysis, the authors chose to study two blocks within the C6-4X zoning district,
located along 6
th
avenue between West 26
th
and West 27
th
streets. They acquired information regarding
the fragmentation of these blocks into land parcels that reflect property boundaries. As shown in Figure 9,
these blocks consist of small parcels along their long sides and one large parcel along their short side facing
6
th
avenue. The scope of the analysis was limited to the large parcels, as they accommodate high density
tower-on-a-base typology buildings (FAR 12) within a medium density broader context. The hypothesis was
that a new building massing design with equal density but significantly better daylighting performance could
be proposed using the proposed workflow for the aforementioned parcels.
Figure 9. Urban blocks, zoning districts, and land parcels
To define the geometric attributes of the new building massing design, the authors sought to abstract the
formal characteristics of typology A, which significantly outperformed the other typologies in terms of
daylight performance at high density as illustrated in Figure 7. They thus proposed a design with slender
towers sparsely placed on a minimally obstructed contextual base, as described in Table 3 and illustrated
in Figure 10. The contextual base height was set to 8 stories, and the tower height to 34 stories.
Table 3. Geometric parameter values
Parameter
Value
Tower Height
34 stories (102m)
Tower Length
14m (46’)
Tower Width
10m (33’)
Base Height
8 stories (24m)
Floor-Floor Height
3m (10’)
Figure 10. New building massing design within its urban context
To evaluate the performance of the new building massing design (Case A) compared to the existing
condition (Case B), the authors employed the proposed workflow and focused on two metrics.
Contextual Obstruction (sDA
[300lux] [50%]
reduction for surrounding buildings)
In this process, a base case (Case C) was established, that consisted of the surrounding buildings
and the contextual bases without towers. The sDA
[300lux] [50%]
was simulated for the surrounding
buildings in the urban context for Cases A, B, and C according to the simulation settings described
in Table 2. Then the reduction in Spatial Daylight Autonomy (sDA
[300lux] [50%]
) for Cases A and B
against Case C was calculated (C-A compared to C-B).
Daylight Availability (sDA
[300lux] [50%]
)
In this process, both cases were simulated within their actual urban context according to the
simulation settings described in Table 2.
The simulation results were summarized in Table 4 and the setup for all 3 cases illustrated in Figure 11.
Case B performed significantly better for both metrics.
Figure 11. Cases A, B and C within their urban context
More specifically, Figure 12 illustrates the floor-average sDA
[300lux] [50%]
for contextual buildings in Cases A,
B, and C. In Case C, without any high-density tower development, the contextual buildings reach a 22%
daylight availability score. The addition of towers according to the existing zoning regulations in Case A,
leads to a 42% reduction for the sDA
[300lux] [50%]
of contextual buildings, hinting to an intense overshadowing
effect. In Case C, the new massing design of matching density still causes a 32% reduction of its
neighboring buildings daylight exposure, yet manages to limit overshadowing by a significant 24%
compared to Case A. This improvement can be attributed to the sparse placement of the high-density
towers that allows for increased daylight penetration through the massing.
Table 4. Case Study Results
Metric
Case A
Case B
Comparison
Contextual Obstruction
(sDA
[300lux] [50%]
)
13%
(-42% from Case C)
16%
(-32% from Case C)
24% less obstruction
In Case B
Daylight
Availability
(sDA
[300lux] [50%]
)
32%
51%
60% better performance
In Case B
Figure 12. Contextual obstruction for cases A, B, and C
On the other hand, Figure 13 illustrates sDA
[300lux] [50%]
mapped on floor plates for Cases A, B, and an
improved Case B’. In Case A, the consistently deep floor plates of the existing massing design yield a
relatively poor sDA
[300lux] [50%]
32%. Case B appears to be more polarized, with the contextual base reaching
low daylight availability levels around sDA
[300lux] [50%]
20%, while the towers remain consistently above sDA
[300lux] [50%]
65%. The cumulative daylight availability score of the new massing design is 60% better Case A.
To further illustrate the effectiveness of the proposed workflow, the authors proposed an improved matching
density design (Case B’), with a 10-story high contextual base and 14m (45’) by 14m (45’) atriums that
reached sDA
[300lux] [50%]
56%, outperforming Case A by 75%. In terms of daylit area, the improvement for
Case B’ (8,745 m
2
) over Case A (5,542 m
2
) indicates that the proposed design yields higher quality spaces,
hinting to increased profit margins for developers.
Figure 13. Daylight availability mapped on floor plates for cases A, B, and B’
This case study showed that applying the proposed workflow to refine high-density building massing design,
yields prototypes with reduced impact on the solar access levels of the surrounding buildings, increased
daylighting performance, and improved real estate potential. These results could justify the application of
the proposed workflow towards informing and expanding the New York Zoning Resolution in the future.
CONCLUSION
In this paper the authors started with the premise that daylighting potential of buildings is an urban-
scale challenge. After presenting the history of the conflict between urban density and solar
access from a zoning regulation and a research-based perspective, they presented a novel, LEED
v4 simulation-based methodology to establish daylight zoning law and showed its relevance for
zoning boards, urban planners, and real estate developers. The authors believe that this
methodology will allow stakeholders to make more informed, performance-aware decisions
regarding solar access at the urban scale.
ACKNOWLEDGMENTS
The authors would like to thank the Masdar Institute, the Onassis Foundation, and Transsolar
Climate Engineering for funding this research project, as well as Professor Michael Dennis for his
valuable remarks in the early stages of this project’s development.
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