Story at a glance:
- Passive solar design can be difficult—but not impossible—to implement in urban settings.
- Elevated windows, thermal shutters, and self-tinting windows can help make passive solar design a more viable strategy for urban dwellings.
- The Middle Village residence in New York City circumvents non-optimal site conditions via innovative passive solar designs.
Reducing the built environment’s contribution to greenhouse gas emissions is crucial to slowing and eventually reversing the worst effects of climate change—and there are few better decarbonization strategies than improving energy efficiency and minimizing energy consumption through the implementation of passive solar design principles.
And while passive solar design strategies have long been implemented in rural and off-grid projects, they are noticeably absent from many urban dwellings.
This article is intended to serve as reference and inspiration for innovative passive solar home designs in urban settings.
What is Passive Solar Design?
Passive solar design uses the sun’s inherent thermal energy to help passively heat, cool, and illuminate built environments. Photo courtesy of Lance Gerber.
Before we get into the different design strategies, let’s take a moment to talk about what passive solar design is in a bit more detail. Passive solar design refers to the use of the sun’s energy to heat, cool, and illuminate built environments without the aid of extensive mechanical or electrical devices.
As a general rule successful passive solar designs include four core elements or features:
- Aperture. Refers to large glass surfaces through which sunlight enters a building; for maximum efficiency these surfaces should face within 30 degrees of true south and should not be shaded between 9am and 3pm during the winter months.
- High thermal mass. Describes a class of materials (e.g. brick, stone, concrete) with a high capacity for absorbing, storing, and releasing heat over time; during the winter, these materials absorb solar energy and then release that energy for the purposes of heating interior spaces—during the cooling season, these materials absorb heat from warm interior air and release said heat throughout the night.
- Distribution. Refers to how solar heat is transferred from where it is collected/stored to different areas of a building; may be achieved by conduction, convection, radiation, or some combination of the three.
- Control. Includes all devices or features used to shade the aperture area(s) during the summer months; these features may be dynamic (active) or stationary and are typically designed to limit solar heat gain without preventing daylight from entering.
High-performance insulation is another factor that plays a crucial role in passive solar design and helps prevent unwanted heat transfer into or out of a building; this ensures solar energy is not wasted during the heating season while simultaneously preventing excess heat gain during the cooling season.
Many passive solar homes also incorporate natural ventilation to some degree, typically as a way to help facilitate the cooling of high thermal mass/heat sink materials during the night so that they are able to effectively absorb heat again the next day.
Passive Solar Design in Urban Contexts
Regardless of where a project is located, the basic principles and core elements of passive solar design remain the same. Site-specific conditions can, however, make the implementation of certain passive solar design strategies difficult, requiring that more innovative solutions uniquely tailored to a project be devised and employed.
This is especially true in dense urban areas where a combination of high building density, tall buildings, and narrow streets often limits the amount of solar energy—especially that from the low-angled winter sun—that other buildings receive during the day. For this reason extreme care should be exercised when conducting a site analysis for urban homes considering passive solar design; factors like orientation, shading, solar exposure, and even wind patterns all play an important role in determining whether passive solar design is a viable option.
In some cases it simply may not be possible from a feasibility and efficiency standpoint to implement passive solar design strategies in urban settings due to non-optimal site conditions. There is also always the possibility that new development projects may render otherwise functional passive solar design strategies ineffective at a later date; some areas have zoning regulations that protect landowners’ solar access, but that is a rarity more than norm.
Innovative Passive Solar Home Designs in Urban Settings
Large windows and overlapping structural insulated panels are two passive solar design features used by the Urban Frontier House. Photo by Nathan Satran
In this section we explore a few innovative strategies for implementing passive solar design in urban settings.
Elevated Windows
Homes located close to the street level in dense urban areas may not receive much sunlight during the winter months, as surrounding buildings often prevent a significant portion of the low-angled sun from entering through conventionally-sized windows installed at traditional heights on a building’s facade.
If these surrounding buildings are of a similar size to the home in question, however, installing larger windows at a higher elevation—just under the roofline, for example—can help to compensate for this loss in solar radiation collection. Similarly, installing large windows or skylights on the roof’s south-facing angle can help to maximize solar energy collection.
Thermal Shutters
There is, however, a limit to how large and how many windows may be installed before they begin to negatively impact a home’s thermal abilities, as glass is typically a worse insulator than opaque building elements. To help prevent undue heat loss during the night, passive solar homes in urban areas should equip their windows and aperture surfaces with thermal shutters.
As the name suggests, a thermal shutter is a type of window covering designed to provide insulation, reducing the likelihood of unwanted heat transfer through the glass itself. In a passive solar home, thermal shutters should be placed in front of windows as the sun sets (during the warming season) to keep valuable heat energy from escaping as it is gradually released by high thermal mass materials.
Self-Tinting Windows
Receiving too little sun is a common problem for many urban homes in areas dominated by high-rise buildings, but the opposite—receiving too much sun—is also a reality for many new residential construction projects in low-rise urban areas that are largely devoid of tall, shade-casting objects. Too much solar heat gain can make a passive solar home uncomfortably warm even during the winter months.
Installing self-tinting thermochromic windows on north-, east-, and west-facing facades can help to prevent excess solar heat gain throughout the year without sacrificing daylighting in the process. When thermochromic windows reach a certain temperature, they passively adjust their opacity or transmittance level using a phase-changing polymer to reflect a wider range of NIR radiation and minimize solar heat gain.
Improved Thermal Insulation
While a high degree of thermal insulation is important for any home looking to implement passive solar design strategies, it is especially important for those homes in urban settings that may receive non-optimal solar exposure throughout certain parts of the year. Increasing both the thickness and R-value of insulation beyond what is considered standard can help to prevent what little solar thermal energy does enter from escaping.
Examples of Innovative Passive Solar Home Designs in Urban Settings
Now that we have a better understanding of how innovative passive solar design strategies can be integrated into the design of urban homes with favorable—or at the very least, workable—site conditions, let’s take a look at a few real-world examples.
Italian Market Passive House, Philadelphia
Italian Market is the first PHIUS certified single-family home in Philadelphia and leverages the sun’s thermal energy to its full advantage. Photo courtesy of PHIUS
Built above an existing 2,000-square-foot commercial garage, the two-story Italian Market Passive House was the first PHIUS-certified Single Family Passive House in the city of Philadelphia.
Designed by BluPath Design, the home features a double height glass living room facade oriented to face true south in order to maximize solar heat gain during winter; Intus triple-pane UPVC windows are used to illuminate the home’s other rooms, with each window opening being splayed on two sides to help draw sunlight deeper into the interior.
Laser-cut aluminum sculptural shading elements were also installed over the home’s large front windows to prevent undue solar heat gain during the summer months without blocking the low-angled winter sun. Super-insulated walls further serve to limit solar heat gain only to where it is desired and help prevent unwanted heat transfer through building materials.
Middle Village, New York City
Middle Village’s deep window insets reveal the thickness of the insulated concrete forms helping to create an airtight, passively heated environment. Photo courtesy of NODE Architecture, Engineering and Consulting
Designed by NODE Architecture, Engineering, and Consulting to Passive House standards, Middle Village is a 6,300-square-foot luxury home in Queens that employs several innovative strategies to circumvent non-optimal site conditions like the property’s narrow southern face.
“It’s most favorable to have the southernmost facing part of the building include large windows to allow the low winter sun in the house to provide heat,” Jakov Saric, co-founder and principal architect at NODE, previously wrote for gb&d. “However, the Middle Village site’s narrowest point is at the southernmost point of the property, which greatly reduced sunlight exposure at that end.”
To address this issue and maximize solar admittance, NODE installed large opening lift-and-slide glass patio doors with triple-insulated, krypton-filled glazing along the building’s southern facade to maximize solar energy admittance. Balconies and a large roof overhang serve to shield the doors from the harsh summer sun, preventing the buildup of excess solar heat energy without blocking the low-angled winter sun.
Extremely thick walls made from insulated concrete forms help to avoid unwanted heat transfer and strategically-placed windows further serve to collect solar thermal radiation.
Urban Frontier House, Billings, MT
The Urban Frontier House’s garden room helps supply the home with sun-warmed air during Montana’s frigid winters. Photo by Clark Marten
Designed by High Plains Architects (HPA) to meet LEED Platinum standards, the Urban Frontier House shows that passive solar design can be implemented effectively even in climates that experience extreme temperatures.
Despite Billings fluctuating between temperatures as low as -36°F in the winter and as high as 108°F in the summer, the home features no active heating or cooling mechanisms, instead relying on overlapping structural insulated panels, abundant daylighting, and natural ventilation through strategically placed operable windows and skylights to help regulate heat gain/loss throughout the year.
Retractable blinds were also installed to help provide light control and reduce heat loss and gain depending on the season. During the winter, sun-warmed air from the home’s four-seasons garden room is circulated throughout the interior with the help of a 95% efficient Zehnder heat recovery ventilator.
