Issue 19 & 20 - Pages 46-53

The Urban Garden; Industrialized Net Zero Energy Housing


Joseph Wheeler, AIA Andrew Balster Robert Dunay, FAIA


Alireza Borhani (Graduate student)

Greg Catron (Undergraduate student)

Negar Kalantar (PhD student)

Tobias Leibing (Graduate student)

Chris Morgan (Undergraduate student)

Robert Vance (Undergraduate student)


Tim Frank, RA, LEED


Brian Lee, FAIA

Philip Enquist, FAIA

William Baker, PE, SE, FASCE, FIStructE


Richard WIlson, AICP

Arvinder Dang

Jennifer Skowlund

Casey Renner

The promise of factory built housing has risen and receded each decade over the past century, yet has not broken through to mainstream construction. Economy of scale, lower cost, higher quality and faster production are predicted attributes that are now overlaid with concerns of sustainability and energy use. This project proposes a re-examination of industrialized processes and its applicability to high-density living. By integrating architecture and technology, the goal is to make dwelling sustainable and beautiful.

Over the past decade, students and faculty at Virginia Tech have designed and constructed three net-zero energy houses for the DOE Solar Decathlon. These research initiatives have resulted in considerable expertise in sustainable construction and energy efficient dwellings. All three houses were not only top ranking in the architecture and innovation categories, but also were top performers in energy production and energy efficiency. As a detached single family dwelling, the most recent of the three houses has fulfilled its challenge with regard to competition and dissemination of information to the public. However, considering the larger issue of the nation’s energy security and use, new strategies are required to address systemic issues of higher density living and scalable communities. Energy consumption in residential and commercial buildings accounts for 40 percent of our nation’s energy budget. Buildings typically operate at less than 50 percent overall efficiency. The housing industry has been reticent to experiment with new techniques that could make buildings less energy intensive. Houses constructed by small, local trades have not changed their construction techniques in decades. The panelized housing industry and prefabricated factory built processes represent some improvement in speed and waste reduction, but overall the results are conservative and energy saving is minimal.

This research is an initial attempt to apply lessons learned from previous work to crack open new ideas regarding residential, high-density construction and the use of energy in buildings. The goal is to develop and optimize an industrialized building system for low and mid-rise residential units. The initial tactic researches the feasibility and viability of a prefabricated building module. The intention is to merge sustainability, energy optimization, mass production and conservation with market demands and trends.

With the corporate partnership of Skidmore Owings and Merrill, Virgina Tech university research group is proposing (currently designing) a mixed use project on a site in south Chicago which will provide a city block design which includes medium and high density housing. The project is designed as factory built-industrialized and is proposed to reach near to net zero energy performance and will utilize fundamental sustainability practices including passive heating and cooling design strategies and water conservation. The goal for the proposed development in south Chicago is to reach net zero status by utilizing self-generated clean energy and large-scale environmentally sustainable and renewable practices.


Computer Aided Design (CAD), Computer Numerical Controlled (CNC) machines, and Computer Aided Manufacturing (CAM) have been the province of the automotive and aerospace industries. Until recently, design fields have peered with envy at the precision of the structure/ function relation that yields innovative performance. This opportunity is now entering the consciousness of architects and designers, changing the conception and operation of normative practice. Speculation on the possibilities of digital tools in design and architecture are beginning to overcome the discrete specializations that typically govern use.

To date, industrialized processes have been successfully utilized for product-based manufacturing. The automobile industry, for example, has advanced in consistently upgrading their manufacturing techniques to deliver the most precise and high performance product. Comparing present residential construction methods with the advances in product and vehicle manufacturing, we realize there is much potential in rethinking building construction. One challenge remains consistent - the problem of applying new production technologies to old construction processes. Buildings should be designed to capitalize on new processes.

Modular Housing and Mobile Homes

Modular construction involves volumetric components of a building, which are factory manufactured, transported to the site on a flat bed trailer, and set as a single unit or erected into a finished building. Methods of off-site construction are presently utilized, particularly in the mobile home industry.

New Technologies of Production

Factory high volume production commonly house CNC (Computer Numerically Controlled) robotic engineering. High volume production offsets the capital expense of facility and equipment investment; the quality of product is assured; costs are precise; and schedule is predictable. On time/on demand delivery reduces capital needed for advance purchase and storage of components. Weather delays are eliminated and production is possible on 24/7 cycles. Most importantly, factory assembly provides a prime environment for the installation of complex systems for proposed future house technologies.

Quality Control

An enclosed and organized work environment with predictable inventory and fabrication can guarantee a product of higher quality than anything constructed in the field. As buildings become more complex with integrated electronic systems, the demand for a high level of quality control becomes necessary.


Today economies of scale can be achieved through mass customization, which is the ability of certain products to be individually adjusted. At the turn of the last century, exact repetition was the only way to achieve economies of scale. Modular construction, as compared to in-situ construction, can more readily utilize this type of economy. As a result, exact repetition dominated the modular industry during this period, leading to buildings, which were, in many cases, banal. Digital design, Building Integrated Modeling (BIM) computer numeric control(CNC) fabrication technologies, and various systems approaches allow mass customization to replace exact repetition as a means of achieving economies of scale. A direct comparison between on and off site construction shows factory production of housing to yield a 15% to 20% construction cost savings and 50% construction time savings. Conventional cost of construction is about $185 to $200 per square foot. Compared to an assembly line producing ten modules per day, cost is reduced to $160 per square foot. For large-scale housing projects, an on-site factory eliminates major shipping costs. The process guarantees cost certainty and risk reduction.

Current modular production methods yield significant savings in time. Improved design models focused on industrialized production have the potential to decrease production cost, improve product quality control and insure tight, energy efficient construction.


The use of off-site construction has resulted in 50% faster construction time. This brings with it cost certainty, risk reduction, safer construction, a tight envelope, quality control, sustainable materials and limited waste to make the entire fabrication and construction process as efficient as possible.


Off-site factory production provides a safe work environment. Around the clock production utilizing regulated shifts prevents accidents caused by tired and careless, overworked laborers and trades. Quality safety supervision is also available on a 24-hour basis. Safe processes for fabrication can be developed for repetitive and familiar tasks. In addition, with the quality control assistance of computer numerical controlled (CNC) processes, assembly will be made more fluid. With the guarantee of a safe work environment, insurance costs may also be reduced.


With the majority of the construction process occurring in the factory, there is a significant waste reduction. All processes integrate the latest sustainable products and employ the most efficient assembly techniques. Green Building delivery methods are employed to reduce waste and guarantee the use.

Modular Unit

Rapid urban growth requires new ways of design and construction for housing in cities. With an increasing premium for high performance, mass production techniques are playing a greater role in the production of high volume modular components. The possibility for new medium and high-density housing is here. This design strategy centers on industrialized production with two building types - eight story mid rise and twenty story towers. Both types use the high-density typology of the townhouse stacked flat units with a shared vertical circulation core. The standard two or three bedroom flat will be manufactured in three prefabricated components; two simple living modules, one containing the bedrooms and closets and the other containing the living and dining rooms. The third module is the service or “smart module.” This unit contains the kitchen, bathrooms, mechanical room, laundry room and all home electronics including the automated building control systems.

This investigation into industrialized housing takes an existing manufactured module as an initial starting point of study. Measuring 14’ wide, 12’ high and a variable length up to 56’, the structure is steel with a concrete floor. The units are engineered to allow stacking up to 28 stories.

Each dwelling consists of three module types:

The living and dining areas are completely open to allow for expansive views out each end to the city. At each end of the module, there are integrated patios (urban gardens) that can cross ventilate or insulate to respond to inclement hot, cold or windy weather conditions.

This technology module contains the complex mechanical, electrical, plumbing and electronic systems of the house. A full kitchen and audio visual closet and laundry room are also incorporated. This unit remains fixed in plan in relation to above and below units to ensure vertical chase alignment. The completed module includes the following components: energy star appliances, low energy lighting, electronic building control system, passive heating and cooling equipment, hot water system, trombe wall assembly, water efficient fixtures, heat pump system, heat exchangers and duct work.

The bedroom module houses the bedrooms and additional patio space. This module can have multiple bedrooms, an office, or an extended garden depending on configuration and family needs.

The central service component (2) of the plan remains fixed to accommodate stacking chases and complex systems leaving flexibility for the two adjacent bays to accommodate a variety of unit types with optional room and balcony sizes

The Stair Core Module

Another component of both the mid and high- rise schemes is a stair core that is also constructed utilizing stacked prefabricated components. This core provides the required vertical fire separation required between units on the low rise and frames the vertical ventilation shaft in the towers. The stair cores in both building types are naturally heated and cooled through passive systems.

Flexible Plan

Flexibility for adaptation and renovation is a sustainable characteristic. In the urban garden concept, the possibility of varying lengths of the prefabricated modular unit allows for garden terraces and additional bedrooms. The adaptability of the plan provides for one, two and three bedroom units each with varying floor plan arrangements.

The Urban Garden

One of the drawbacks to living in a more dense urban area, particularly a tall building, is the lack of connection to the outdoors. When a young couple makes a move from the outer suburbs to the city, they regret leaving their private gardens and landscapes. The proposed scheme provides a strong connection to the landscape though urban gardens. As a major part of the passive strategies for this project, each housing unit will have an expansive exterior garden patio on each side of the living space. These garden patios can open completely during the warmer summer months providing cross ventilation or close like greenhouses in the winter months to serve as insulating buffers to the indoor space. Large terraces with year round gardens become extensions of the living and bedroom spaces. During moderate weather these rooms physically become extensions of the interior floor plan. In extreme weather, the terraces become passive mechanisms for making the home more energy efficient. The greenhouses also shelter garden plants in the winter, preserving the garden for year round enjoyment.



An underlying theme for this research is the development of one city block for a new development master planned by the SOM office. The site was previously occupied by the US Steel Southworks Mill, located approximately 10 miles south of Downtown Chicago.

City Block Plan

Mid-rise units are oriented north south and stretch the full depth of the row with arrangement of balconies strategically located integrating inside and outside to maximize summer and winter use. It is a different type of domestic experience centering on urban gardens. The south walls of the living spaces open as a garden in summer and close down as greenhouses in winter. The north balcony gardens provide a refuge from the hot summer sun. Natural cross ventilation, particularly across the living and dining module and passive heating collected from the south sun help optimize energy use. The proposed tower units located on the short sides of the block are articulated toward the east with the cores situated to the west. Each unit has views of the lake. Single loaded units take advantage of sunlight, passive gain and cross ventilation. The towers are articulated to allow a view of the lake from the mid-rise units and to maximize sun exposure to the center of site.

The Southworks Solution: Townhouse Flats

A similar typology to the row house is the stacked flat townhouse. The organization involves horizontal flats stacked four units high with a shared pair of stairs. The type allows wider exposure to the street and rear since the unit widths may exceed 25 - 30 feet. By widening the plan and narrowing the depth, passive solar and cross ventilation strategies can be successfully incorporated with this housing type. Medium and high-density housing can be obtained with the stacked flat type with the addition of an elevator and stacked internal block parking.

It is an expensive step but can increase the housing density exponentially to above 75 units per acre. These types also require fire separation and mechanical ventilation. It is this latter typology, which this research project will adopt to provide the number of units required for the master plan specifications. In the proposed concept, medium density townhouses stacked eight units tall for mid block and 20 unit stacked towers flanking each block are utilized.

City Block Development

The Urban Garden mixed-use city block provides a range of building types, that make the Southworks development an active 24-hour urban neighborhood. The city street is lined with two levels of retail and service buildings, mid blocks from the third to the eighth level will be Chicago flat style townhomes with a mix of one, two, and three bedroom units.

Scalability of Neighborhood

Developers can phase the mid-rise residential complex by staging the project in floor levels. If the eight story master planned complex is adequately sized structurally, the project can rise in stages as needed. Stacked cores can be lifted vertically, refurbished with new technologies, systems, kitchens and bathrooms and replaced without major reconstruction or renovation. Like computers and upgraded software, the houses can easily be updated with the amenities and technologies of the day.

Scalability of Plan

The central service component of the plan remains fixed to accommodate stacking chases and complex systems leaving flexibility in the two adjacent bays to accommodate a variety of unit types with optional room and balcony sizes. Flexibility for adaptation is a sustainable characteristic of a building and the modular building unit allows for variation within a repetitive system.

Modular Tower

For higher density housing, the proposed tower units are articulated toward the east with the cores situated to the west and serve as bookends for each city block. Each unit has views of the lake. Terraces are integrated into the massing to control solar shading, and the plan is optimized for natural ventilation through a solar chimney circulation tower. This circulation zone creates a ventilation stack and a vertical garden that gives each resident a semi-private green space within a new neighborhood typology. The modular concepts seen in the mid-rise areas of the complex have been applied to the high-density housing of the tower. Modules shift to allow for greater solar access, larger outdoor living and garden spaces. At the plaza level, the bases of the towers create terraces that frame views of Lake.

Michigan and establish a relationship between the mid-rise and high-rise developments.
Reduced height of the east tower provides for greater sun exposure of the site. A significant mass removed from the base of the east tower offers the low-rise units a window to the lake.


District Energy Strategy

The Southworks community is planned to be a near, net-zero energy development. The proposal suggests that the new city block will receive all of its power from a combination of clean energy sources. Sources include wind energy produced by turbines located on Lake Michigan, fuel cells powered by local landfill methane, and alternative energy generation within the complex. Energy efficiency is obviously a critical aspect of a net-zero system. Therefore, much research will be dedicated to developing a district community which utilizes passive strategies incorporating the most energy efficient systems for operation. By utilizing the Earth’s mass as a heat source/sink, geothermal systems coupled with heat pumps rank among the most energy efficient means to heat and cool buildings. Structurally integrated geothermal piles reduce construction costs by combining systems. Though the EPA does not sanction geothermal loops submerged in Lake Michigan nearby, energy can be harvested from lake water passing through the nearby water filtration plant before distribution to the city.

Solar thermal collectors will generate hot water year round for seasonal hot water storage. This large supply of tempered water will supplement the geothermal supply to guarantee energy efficient heating operation throughout the cold Chicago winters. This tempered hot water can also be collected through water loops under sidewalks and paved surfaces in summer and reverse operation in winter when snow melt is required.

District wide systems, due to the higher volume of production and consumption, are inherently efficient. This complex will incorporate district scale operation ranging from localized HVAC systems to public utilities and mass transportation strategies.

Natural Ventilation Strategies

Decisions for the placement of openings in the building’s envelope for natural ventilation strategies are determined by the dominant wind directions, speed, and wind temperatures of the building location. The goal is to provide fresh air supply and to temper the space for as many hours as possible passively via natural ventilation. The analysis at right of natural ventilation explores the movement of fresh air throughout the unit interior without the use of mechanical systems. This airflow simulation uses a computational fluid dynamics program to calculate the interaction of air with the unit partitions defined by boundary conditions. This example shows that the openness of the unit draws between a light breeze and a noticeable draught through the interior spaces. The directional airflow vectors also suggest that there is a light circular draught that moves within the largest urban garden space. Future research into more specific aspects of natural ventilation will examine the introduction of the vertical stack, ventilation chases within the unit, and the impact of operable exterior skin panels on the behavior of the natural airflow within the medium density unit.

Water Conservation - Water Management

There are three primary reasons for conservation of water resources, particularly in regard to sustainable and net-zero energy development.
• To save energy; water delivery, potable water filtration and waste water treatment account for approximately 15% of energy use in major cities.

• To conserve water resources; the goal is to draw less water than the natural process
can replenish thus preserving a balanced ecosystem.
• To preserve our natural habitat; maintain balanced ecosystems for delicate wildlife habitats

The Southworks development utilizes water conservation methods at multiple scales. The largest scale involves district rainwater harvesting and wastewater treatment/recycling. The smaller scales involve efficient use of domestic supply through the use of water efficient appliances and fixtures. A larger scale system viable for the Urban Garden scheme is the Living Machine wastewater treatment concept which utilizes the garden landscape to process wastewater for reuse. Another viable model can be referenced from Germany’s “biovillages” which burn processed waste, wood chips and crops at the district wastewater plant to generate electricity.