perFORMance
a project by Ari Bible, Adriana Salim, and Eva Yunqi-Wei for Giovanni Betti’s Spring 2021 ARCH 249: The Performance of Form at UC Berkeley CED
MARKET STREET SITE
The design area occupies a one-block site just southeast of Market Street, bounded also by 12th, Otis, and Gough Street in San Francisco. At the Market Street site, analyses will have to take the urban surroundings into consideration, paying special attention to noise and privacy concerns around this busy area.
The block is presently home to a school, a free clinic, restaurants, and various commercial as well as residential programs along with a significant area of surface parking. It’s ripe for redevelopment to increase density and bring life to outdoor public spaces within the block while maintaining the diversity of programs housed. The area is relatively flat, with a slight slope down to the southeast. Surrounding plots range from surface parking lots to high rises over 20 stories tall, but no nearby tall buildings significantly affect sun exposure within the site.
CLIMATE ANALYSIS
This project is sited in San Francisco, California, and a climate analysis of the area was performed prior to beginning the design process. Using the CBE Clima Tool and Ladybug Tools, this analysis began with a preliminary look at the local climate and UTCI comfort conditions over the course of a year.
The above analyses of hourly outdoor comfort under various sun and wind conditions indicate that, overall, sun exposure is desirable in San Francisco, while wind tends to decrease thermal comfort in this moderate climate, especially in the winter. As the upper right, No Sun + No Wind, chart shows, the dry bulb temperature is generally comfortable throughout the year, with the exception that some mid-winter days can get too cool for comfort.
This chart illustrates that sunlight plays a decreased role in thermal comfort from October through March. This is largely because the winter is a wetter, more overcast season in San Francisco. The graphic also indicates that, before the day warms up, the sun plays a significant role in raising UTCI through spring and summer mornings.
Although wind speeds tend to be slightly lower during the winter, winds have a greater effect on thermal discomfort through the winter months when temperatures are already lower.
COMFORT CONCEPTS
Winter Comfort
The climate analyses indicate that San Francisco’s climate is generally comfortable between April and October. Having established November through March as the least thermally comfortable time of the year, the aim of the remainder of the project will be to seek to apply appropriate massing and programming strategies on the site to optimize comfort through this period. In the winter, maintaining maximal sunlight while blocking cool northwesterly winds is key to enabling comfort for outdoor activities.
Climatic Pleasure
Various combinations of shade/sun, breezes/blocked winds, and busy/quiet programs generate a dynamic experience moving through the site, where visitors are able to locate and occupy which areas are best for them.
Temporal Programs
As sun and weather conditions shift both throughout the seasons and over the course of each day, the ways that spaces are used shift accordingly.
PROGRAM + CLIMATE
Analyses have been tailored to the Bay Area’s Mediterranean climate, focussing particularly on the cool, wet winter months which have been assessed as the least thermally comfortable time of the year. From November through March, discomfort is generally caused by low temperatures and compounded by cloud cover and winds; thus, interventions should seek to maintain high sun exposure while blocking dominant northwesterly winds.
For the purposes of this project, we propose that the Market Street site will benefit from an intervention that assumes a blank slate bounded by Market, 12th, Otis, and Gough Street, with mixed-used residential, commercial, and civic buildings around the perimeter and a significant central area of public green space for a park, an outdoor market, and arts and culture programs within the more sheltered interior of the block. Inspired by the single-lane streets already permeating the block, alleys provide pedestrian (and occasional vehicle) access to this public courtyard park. This proposed intervention allows all current occupants to remain within the block while significantly expanding residential capacity and public space; it will bring a new and much-needed area of green space with a public performance venue to the neighborhood.
Building massing is guided by sun and wind conditions and shelters the public courtyard park from winds and the bustle of nearby streets while maintaining high sun exposure through the winter months. This outdoor space hosts a variety of programs including a park, a performance venue, and food truck and farmers markets; it will include variously shaded and sunny, sedentary and active, and soft- and hardscaped areas, allowing users to gravitate toward the areas best suited to their needs and personal comfort as needs and conditions change.
Activity level and metabolic rate are important factors in determining thermal comfort. As such, any thorough analysis relating programmed areas and outdoor comfort conditions must consider the activity levels of users. The chart to the left demonstrates how Metabolic Equivalent (MET) affects comfort across various UTCI categories. For context, 1 MET is the energy expended by a person at rest, while a person walking briskly at 3–4 miles per hour typically expends around 4 METs.
For most outdoor programs, sunlight will increase thermal comfort during winter months; exceptions to this generalization include street cafes and the performance venue, where shade or less sun may at times be desirable to reduce glare or provide shelter. Just as allowing sun is advantageous, a similar rule applies to the blocking of wind in all except for the most active spaces, such as the park and sports field, and possibly circulation spaces like alleys as well.
Sun and wind conditions vary with the time of day, so it is also handy to understand when each program is likely to be in demand and to focus on those times when performing program-specific climate comfort analyses. In addition, a quick temporal use analysis reveals that not all programs are likely to be used at all times, and situations.
DESIGN GOALS
Greenspace
A large area of public open space houses various flexibly programmed environments. This green space will be protected from street noise by buildings around the perimeter of the site.
Mixed Programs
Residential, office, commercial, and civic uses surround the open space. The central green space accommodates a variety of park, sport, performance, cafe, and market programs.
Year-Round Usability
This project is primarily concerned with enabling the design and analysis of an outdoor space that will be comfortable for a wide range of users and uses through the area’s changing weather conditions. Although the exterior area is of primary interest, it’s approached through shifting surrounding building massings.
INTERVENTION
On the Market Street site, a courtyard arrangement of mixed-use buildings around a central public open space is best suited to the block. With this approach, an enclosing perimeter of built area protects the open space from street noise and cool winds, and building masses are further tailored, with increased heights toward the northwest end of the site to further block winds and shelter the courtyard. In addition, building masses must be thoughtfully formed to allow maximal solar radiation into the courtyard and onto building facades — this means that building heights will be lower toward the south, while denser built areas will occur on the north side of the site. Luckily, the sun and wind requirements on this site do not conflict, and both needs are met by this massing approach, which provides improved thermal comfort for outdoor activities through the cooler portions of the year.
The courtyard block design simultaneously increases density, accommodates new and existing programs, and generates new public green spaces, all of which can serve the local neighborhood while enhancing a sense of place. In addition to the large-scale urban design, massing, and programming measures, the inclusion of shade trees, other greenery, and variously sized open spaces within the site will ensure that portions of the area are comfortable for many activities throughout the entire year.
DESIGN INTERFACE
Define Site Boundary
At the Market Street site, the boundary defines a square block. The user may choose to define the boundary set back from the block’s extents, and this feature also allows this app to be transferred and applied to other sites — the program could be expected to perform well anywhere with similar sun and wind conditions. Whatever the Site Boundary, it must be drawn as a closed polyline on a layer named Boundary.
Draw Courtyard Boundary
On a layer called Courtyard, a closed polyline must be drawn at least partially within the site boundary to define an open space. For a true courtyard, this boundary should lie entirely within the Site Boundary, but, if the Courtyard Boundary intersects with the Site Boundary, the program can also function with a partially open courtyard that abuts one of the surrounding streets.
Draw Alley Lines
On a layer titled Alleys, the user can draw any number of lines where paths will run from surrounding streets to the courtyard. Each of these lines must intersect with the site boundary at one point and the courtyard boundary at another point. These lines will serve as the centerlines of access roads connecting the courtyard and the streets bounding the site.
Modify Alley Widths
All of the alley widths can be adjusted simultaneously using a slider in the Control Window. The program also automatically generates a vertical line on the AlleyWidth layer at the interior end of each user-drawn alley line; the user can pull the top control point of this vertical line up or down to increase or decrease the width of an individual alley.
Modify Tower Heights
Tower heights are generated by the script to gradually shift from tall to the North/Northwest to low toward the south, a scheme designed to block winds while allowing sunlight. By pulling the points of the courtyard boundary curve up and down, the user can adjust tower heights around those areas. The building heights will follow the line of the three-dimensional courtyard boundary, with maximum heights in certain areas limiting this relationship.
FEEDBACK
This application is structured to allow a lot of freedom of choice within the typology of a courtyard while still guiding the user toward a design that is effective at maximizing outdoor thermal comfort and sun exposure throughout the site. The user may have unanticipated constraints or priorities, so the program allows for tailoring, revision, and live iterative analysis.
Adjustable Features
- Site Shape and Size
- Courtyard Shape and Size
- Alley Positions
- Alley Widths
- Podium Height
- Tower Position
- Tower Scale
- Tower Complexity
- Tower Height
Simulation Tools
- Sun Hour Simulations of various periods (seasonal or year-round)
- Sky View Simulations
Analytical Metrics
- Site Area
- Courtyard Area
- Gross Floor Area
- Floor Area Ratio
- Total Facade Area
- Sky View proportions above and below 20%
ANALYSIS
Sky View
Glazed facades and exterior spaces should have at least 20% sky view. If greater than 5% of a facade has deficient sky view, then the design should be reconsidered.
Sun Hours
Glazed facades and exterior spaces should see at least 1000 sun hours/year. Sun is desirable at adjusted temperatures less than 23°C, and shade is desirable at adjusted temperatures above 24°C. The interface allows Sun Hours to be analyzed over the course of an entire year or over a specific period of time. Analyzing sun hours during the winter (when this value will be lowest) is likely the most useful application of this feature.
Wind Comfort
Wind is desirable from 15° C to 35°C, but it should be less than 10 mph for sedentary programs and less than 20 mph for active programs.
While tools like InFraReD promise to allow quick and convenient wind analyses, we’ve not yet been able to integrate this technology into our grasshopper scripts. Instead, the program described here takes a broad approach, with most significant masses placed to shelter the courtyard space from dominant winds. Preliminary analyses indicate that this approach is sound; the courtyard should remain relatively still, and what winds do occur are concentrated in alleys, which, as circulation spaces, tend to remain thermally comfortable even with moderate wind speeds.
Thermal Comfort
UTCI equivalent temperature is considered optimal from 20°C to 28°C.
For easy analysis, the grasshopper script outputs a gradient map of thermal comfort conditions onto the ground within the Site Boundary. This gradient indicates which areas are deemed to be too warm, too cool, or comfortable given a target UTCI value that defaults to 24°C.
Program Fitting
Taking as input the Thermal Comfort Analysis of the site and a set of programs with defined areas, MET values and preferred sun and wind conditions, the grasshopper program can project a number of possible program arrangements for the user to consider and adjust. This analysis matches the programs’ requirements to areas of the site which best meet them, prioritizing sun, then MET, then wind conditions.
VIDEO
OUTCOMES
All of these example outcomes are produced solely through the programs and features described above, without post-editing or revision after being output from grasshopper. Although all of the schemes shown here are largely rectilinear, they needn’t be. As the demonstration video above shows, the program allows courtyards of any shape and buildings of various forms as well. Besides optimizing winter climate conditions in the courtyard, one surprising benefit of these designs is that, to varying degrees of success, their massings mediate the changing urban scale along Market Street.
Modified 9-Square
This scheme keeps things simple, with 9 rectangular towers of approximately equal footprint and narrow allesy of equal widths. Examining the yellow sky view analysis image, it’s clear that towers tend to maintain great sky view when positioned with adequate space between them. In this scheme, unacceptably low sky view conditions only occur within the narrow alleys. Reexamining the eastern corner of the site, repositioning the westernmost tower, and widening each of the eight alleys would likely render even this preliminary result an acceptable option when it comes to sun exposure.
Broad Towers
This massing approach aligns all towers with the exterior edges of their podium bases so that the courtyard is framed not by tall towers but by lower buildings that step up to the towers along the street. The five alleys vary in width in this scheme, and, while the narrower alleys have poor sky view, this is acceptable given the typology and anticipated use of these areas. Towers in this scheme are narrow to allow for a generous courtyard space. To maintain density, the towers also become wider and taller, and there are fewer of them, which results in poorer sky view on the lower levels. With fewer alleys and fewer towers, sun-hours and sky view issues which tend to be caused by close positioning of buildings are partially mitigated; however, there’s less easy access to the courtyard by the public. Especially with so few and some very narrow alleys, the courtyard within this block risks feeling like a private space not meant for wider neighborhood occupants.
Urban Scale Mediator
Notable in this scheme is that the towers along market street step away from the thoroughfare, opening the street up and presenting a more welcoming connection between Market Street and the public courtyard within the block. The largest and northernmost building in this scheme has been angled to avoid any interior corners (which tend to have poor sky view and sun exposure). The towers in this scheme maintain acceptable levels of sky view overall, with the exception of the westernmost two towers, which are positioned too close together. Other than that, the only areas with inadequate sky view are those that occur at the podium level around the seven alleys. Out of the three schemes shown, this option has the best sun exposure in the courtyard.
CONCLUDING THOUGHTS
Although the grasshopper scripts developed for this project provide useful analyses of the schemes they generate, the courtyard typology is a significant limiting component. It’s of interest to further explore how such design-assistive programs could be developed to suit a wider range of scales, sites, and conditions, with analyses more applicable to different locations. Some aspects of our program are hard-coded, but they could be more elegantly integrated; for example, the dominant wind condition could be extrapolated from a .epw file rather than built into the design scripts. These analyses could also be tailored to particular seasons or even shorter periods, and the period analyzed could be adjusted easily in the UI.
There are a number of additional constraints and conditions which it might be useful to be able to adjust within the user interface. A few of these include minimum and maximum building heights, minimum Gross Floor Area, maximum distance between alleys, and minimum distance between towers. However, at the same time as it would be exciting to make the programs do more things, it’s also vital to keep things only as complex as they need to be so that the interface can remain comprehensible and usable. Perhaps there’s a way to first ask the user what factors they’re interested in analyzing and adjusting and then generating an interface with only what the user needs.
Although more work remains to be done on numerous aspects of this project, it has served as a useful learning tool for its creators, students still new to grasshopper (let alone all of the plugins used here), it’s been a great window into some of the applications of graphic programming within Rhino to formalize design relationships and aid in generating and comparing numerous schemes based on actual climate, program, and contextual conditions.