When it comes to energy efficient buildings, what often comes to mind are active design components like modern appliances, LED lightbulbs, electric vehicle (EV) power walls, and energy generation and storage capacity. While those are important aspects of sustainable construction—especially for retrofitting existing homes—there are many passive design strategies that can improve energy efficiency and home comfort from the outset by focusing on the building envelope, siting, and orientation.
Passive design strategies are an effective way to decarbonize homes and provide a huge boost to residential energy efficiency, especially when used alongside active design solutions. Where active design seeks to produce the same thermal comfort, ventilation, and lighting services using less energy, passive design seeks to reduce a home’s need for these services, making it possible to downsize systems or eliminate them entirely. Integrating passive design strategies with thoughtful considerations of regional climate can reduce home energy demand by 80% to 90% from code-minimum construction.
Building on the Past: Passive Design Then and Now
Although there has been a recent surge in passive design interest—including research, accreditation programs, and construction—passive design is not new. In fact, passive design strategies have long been employed in human dwellings. Prior to the widespread use of fossil fuels and industrial energy production, technologies like air conditioning, central heat, and lighting weren’t available. This meant that homes had to be well-adapted to their environment to meet occupants’ thermal comfort, ventilation, and lighting needs. According to the American Institute of Architects California (AIA CA), passive design was an integral part of building construction until well into the 20th century.
For example, in the 18th century, it was common for builders to site buildings to best capture prevailing breezes and winter sun, while using the locations of windows and doors to maximize and control ventilation. Even earlier, central courtyards in the Roman Empire were common in domestic architecture as a means of promoting airflow during hot, dry Mediterranean summers. The National Park Service’s Technical Preservation Services division notes that architectural features like porches, awnings, and skylights were developed to meet ventilation and thermal regulation needs in homes of the time. In hot climates, high ceilings of at least 10 feet were essential to home cooling, and in many climates, masonry walls provided greater thermal mass to better regulate temperature throughout the day. These, and other historic influences on climate and site-specific design, orientation, and materials, persist today.
However, new knowledge and materials have continued to improve passive design capabilities, making it possible to dramatically improve building efficiency and performance compared to historical precedent. This has resulted in a notable difference between modern passive design and how our great-great-grandfathers built their homes. Principally, better insulation materials, enhanced construction methods, and a greater capacity to completely seal buildings have meant that new passive buildings require mechanical ventilation, rather than relying entirely on cross-breezes or thermodynamic processes. While window orientation and natural airflow are an important consideration in passive home design, today’s designers emphasize control over the air entering and leaving the building envelope. A sealed building minimizes heat gain or loss, and, importantly, guarantees better indoor air quality (IAQ) by allowing for safe, healthy ventilation even when outdoor air quality is poor.
Passive Home Design Techniques
While the final design of a passive home is informed by the environment in which it is built, there are consistent best practices and considerations that many passive homes share. Many of these practices can be applied to both new and existing structures, and it is possible to retrofit an existing home to meet passive standards. The three basic principles of passive design are:
1. “Tight” construction: An important aspect of modern passive design—in both new and existing construction—is to minimize the transfer of air between the building envelope and the outdoors. For new buildings with mechanical ventilation, construction should aim to create a completely sealed building envelope. For existing structures, the general goal is to reduce, but not eliminate, the transfer of air into and out of the building envelope. Completely sealed construction usually isn’t practical or advisable for building retrofits except as part of a gut renovation, like this cool project by Patriquin Architects.
2. Use the right materials: Passive design requires detailed attention to climate. A home design that performs well in California will look very different from one that performs well in Alaska. For example, homes in colder climates will benefit from windows that allow for greater solar heat gain than those installed in hotter climates. Additionally, passive design standards specify light colored paint in hot climates due to its higher albedo. While paint color is not viewed as a significant factor in cooler climates, light paint can significantly lower solar heat gain, making it a powerful tool in hotter climates. Climate will also influence other materials such as insulation and roofing. Whether choosing materials for a new build or renovation, the right materials go a long way towards achieving a passive home.
3. Know your site: Microclimates and the physical building site also influence passive design strategies. Common design considerations include the orientation of the home and its position on the site. Orientation and position are important because they can help a building take advantage of passive heating and cooling benefits such as natural sunlight and ventilation. For new construction, orienting buildings with the long axis pointed east-west often provides better control of solar energy. Additionally, this orientation provides a longer south-facing roof span, which is useful for solar arrays. Performing a daylight analysis early in the design process can help with identifying sources of shade and light at different times of day. This information can also inform strategic window placement and can help optimize (not maximize) natural light while minimizing solar heat gain.
While owners of existing homes may not have flexibility with building orientation and position, paying attention to site-specific variables can still improve energy efficiency. Understanding sources of solar energy and natural ventilation can—and should—inform home improvement projects.
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Cover image credit: Pablo Ibañez via Pixabay