San Antonio will add 1.1 million people to it’s population by 2040. In 25 years, this influx will bring the population of the city from 1.4 million to 2.5 million, requiring 500,000 jobs and an additional 500,000 units of housing.
“Housing a Million” provides more affordable housing and increases residential density, engagement, inclusion and typological diversity in existing neighborhoods. The proposal places micro-units, which comprise a small studio apartment with a fully functioning kitchen and bathroom, in the backyard of existing homes. This proposal transforms an under-utilized backyard into a new community space featuring green space, parking, bioswales and walkways.
The site for this project is an existing neighborhood in south San Antonio, Texas, USA, near the intersection of Nogalitos Street and South Zarzamora Street. The micro-units can accommodate 10% of San Antonio’s projected population growth, or about 50,000 people.
Measure 1 : Design / Innovation
The building concept is driven by modular Structural Insulated Panels (SIPS), taking advantage of the system's multiple efficiencies: pre-fabrication, modularity, low-cost, ease of assembly, and potential for energy conservation.
Prefabricated and readily available, SIPs offer quick, relatively-low cost installation. The building plan is organized on a 48” square grid, taking advantage of the most commonly used SIPs panel of dimension of 4’x 8’. The load-bearing SIPs panels create an inexpensive, air-tight building envelope, reducing the energy use and construction cost.
Measure 2: Regional / Community Design
In the next twenty-five years, 1.1 million people are projected to move to San Antonio. Most will come for school, job opportunities, or affordable housing. In order to accommodate this growth, without significantly increasing the metropolitan land area by 2040, San Antonio needs to increase its density by an average of 95 persons per square mile, per year.
As the population rises, San Antonio will require new housing typologies that help prevent the advance of low-density suburban development. The addition of micro-units adds an average of 3 people to an average residential lot. The net result will be to double the population of an average neighborhood, while diversifying the available housing typologies and corresponding socioeconomic, demographic and educational profile.
Measure 3: Land Use / Site Ecology
The project generates community space between the new micro-units while increasing the percentage of native grass, native plants and deciduous trees in the existing neighborhood. The neighborhood enjoys a mature canopy of the trees that will provide shade and shelter to residents as they travel from the street to the new micro-units adjacent to the alley. Runoff rainwater will be collected through the use of permeable and bioswales, which will filter water before discharging it into the storm sewer. The layout of these community spaces is designed to provide a comfortable and performative landscape that will help protect against San Antonio’s harsh summer sun and frequent flooding.
Measure 4: Bioclimatic Design
San Antonio has a humid, subtropical climate with hot summers and mild winters. The coolest months are December and January, with an average low temperature of 38 degrees Fahrenheit. The warmest months are July and August, with an average high temperature of 95 degrees Fahrenheit and significant amounts of solar radiation. To address these conditions, the micro-unit utilizes four primary design strategies: window systems with operable shading and low SHGC protect the building against unwanted heat gain; an air-tight and well-insulated envelope that reduces the heat transfer through the building skin in winter; large shaded south-facing windows allow the admission of winter sun while protecting against summer sun; and cross-ventilation through operable windows that provide occupant comfort when the weather allows.
Measure 5: Light and Air
The micro-units offer a south-facing façade comprised almost entirely of windows and an operable shading device. The shading panels open upwards to create an overhang that lets sun in during the winter, but blocks direct sunlight during the summer. Cross-ventilation through north and south allow the interior to be cooled by letting warm air escape through the clerestory windows, providing natural ventilation throughout the year. The units are organized around a courtyard which maximizes the possibility for natural ventilation while providing for shared and shaded outdoor space.
Measure 6: Water Cycle
The average rainfall in San Antonio is relatively low, at 30 inches annually. Therefore, it is important to collect and conserve as much rainwater as possible. The roof is designed to collect and store rainwater in cisterns to be re-used as greywater for bathrooms and irrigation. Low- flow water fixtures also contribute to the economic and water efficiency of the units. Bioswales use native flora, soil, and a gravel liner to treat water before it infiltrates into the local Edwards Aquifer. Aside from bringing color to the neighborhood, bioswales are strategically placed to capture and filter runoff water from paved streets, sidewalks, and roofs.
Measure :7 Energy Flows / Energy Future
The energy costs associated with air conditioning in this region are significantly higher than for heating. The analysis of form, openings, shading, and orientation using Sefaira led to the compact linear form of the micro-unit. During the extreme times of the year, the micro-unit is equipped with a small mini-split system to help regulate the interior temperature. The goal of the project is to generate a micro-unit that minimizes costs for cooling and illumination. The interior is organized to provide a well-lit space that helps reduce the consumption of electricity. The photovoltaics, located on top of the roof, generate more than 30% of the energy consumed.
Measure 8: Materials / Construction
Both the envelope and the structure of the building are made out of SIPs. SIPs are prefabricated, limiting the amount of waste used during construction, making them a quick and easy way to build a home. SIPs do not contain any volatile organic compounds or other harmful chemicals and are made out of foam, oriented strand board, and adhesive. The panels create an air-tight envelope allowing for control of the indoor air, filtering out pollutants and allergens, controlling the moisture in the air, and decreasing the possibility for mold. The micro-unit is comprised of only two different size panels, 4’x 8’ and 2’x 4’, thereby limiting material waste and simplifying construction.
Measure 9: Long Life, Loose Fit
The larger impact of this proposal is to increase the range of housing and transportation choice in the neighborhood. By adding new and smaller unit types to an area that currently features just one housing type, the neighborhood invites different ages and income levels. This proposal also adds walking and biking trails in the existing alley, which will increase the number of transportation options available to neighborhood residents. The goal is to provide low-income residents of the Nogalitos Neighborhood with more housing and transportation options as their families and economic circumstances change over time.
The micro-unit kit contains a water collector system, photovoltaic panels and a native planting scheme. These features will make the neighborhood more sustainable over a longer period of time by decreasing water use, increasing energy generation, and decreasing the negative impacts of monoculture planting schemes. The common area in between the homes provide a flexible use of space, which promotes long-term community. Ideally each micro-unit will increase the population by adding 3 people per lot. The goal is to provide a home for 50,000 of the 1.1 million projected residents of San Antonio, thereby slowing the expansion of low-density suburbs.
Measure 10: Collective Wisdom / Feedback Loops
The micro-unit offers residents a high performance building and the tools to engage in sustainable, affordable living. The micro-unit kits will provide critical information to the owners, explaining the assemble of the building, systems, materials and maintenance. The community areas and proposed landscape will include labels that explain to residents how their new performative landscaping strategies are reducing water consumption, storm runoff, and pollution to the Edwards Aquifer. Our goal is to educate the community about the direct connection between good design, energy consumption, economic well-being and environmental sustainability.