Passive House: An In-Depth Guide
Passive House is a rigorous, performance-based, energy efficiency construction standard. It consistently and predictably provides a high level of comfort, even in the most extreme of weather conditions. Passive House is the highest energy efficiency standard for buildings in the world.
What Is a Passive House?
Homes built to the Passive House standard use a building envelope's first approach consisting of insulation, air sealing, and no thermal bridging. Windows, doors, and any other penetrations in the building envelope are all extremely high-performing. A Passive House is oriented to best take advantage of the sun's energy for heating in the winter and shade in the summer.
There are certification levels within the Passive House Standard. A building that achieves Passive House Plus certification is net-zero. One built to Passive House Premium will be net-positive energy usage. All Passive House's will reach an 80-90% reduction for space heating and cooling demand than the current code minimum. There is also a Passive House certification program for retrofits called EnerPHit. These upgrades have reduced homeowners' energy usage by up to 93%!
Passive House offers the opportunity for homes to be resilient, healthy, economical, and environmentally friendly. They protect the homeowner from possible rising energy costs and extreme weather conditions. They also provide a very high comfort level throughout the year and superb indoor air quality due to the continuous provision of fresh, filtered air throughout the home. They can have a significant "feel good" factor by dramatically reducing your home's environmental impact. A Passive House avoided a whopping 128 tons of carbon dioxide emissions versus a conventional home over 20 years in one case study.
It is important to note that any building can be built to the Passive House Standard - from schools to apartment buildings, churches, community centers, grocery stores, factories, and offices. The "house" in Passive House is just a translation from its origination in Germany as Haus.
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What Is the History of Passive House?
The first Passive House was built in Germany in 1990 (pictured above). The first home built to Passive House standards in the US was completed in 2003 by Katrin Klingenberg in Urbana, Illinois. Since then, the number of buildings built to passive design standards has skyrocketed. As of 2016, there are over 60,000 Passive House buildings in over 45 countries worldwide. Many Passive Houses often historically follow European architecture aesthetics, but any aesthetic preference will work.
Buildings have been built using passive solar building principles since before the 1970s. The US Department of Energy (DOE) and the Canadian government spearheaded experimentation with these principles.
Passive House Standards
There are currently two Passive House standards: The International Passivhaus Standard and the Passive House Institute US Standard (PHIUS).
International Passivhaus Standard
The International Passivhaus Standard was developed by the Passive House Institute (PHI), an independent research institute in Germany, after reviewing previous passive solar designs worldwide. This standard was launched in 1988 and is now prevalent in buildings around the world. Houses have been certified in all climates using the International Passivhaus Standard, most of which are in European countries. The Passive House Institute emphasizes research, testing, verification, open-source sharing, and continuous improvement. The Passive House Planning Package (PHPP), the excel-based energy modeling software forming the standard's backbone, has progressed to version 9.6. PHI is the definitive resource to learn more about passive house principles.
Passive House Institute - US Standard
PHIUS+ is the "made in America" version of PHI. Buildings built to PHIUS+ standards use 40% to 80% less energy than conventional buildings, proving environmental and economic value. PHIUS has been responsible for the certification of over 4.2 million square feet in North America. PHIUS standards were first developed in 2003, formalized in 2015, and updated in 2018 to become PHIUS+.
Five Core Principals of Passive Design
Both standards require strict performance metrics to provide predictable results and incredible comfort, and both follow five core principles.
Principle #1: Super-Insulated Envelopes
Passive house design starts with continuous, super insulation around the building's entire shell, insulating the slab, walls, and roof. To meet the performance metrics, Passive Homes generally require double the code minimum amount of insulation. Fortunately, many high-performance insulation options are also natural and environmentally friendly, including sheep's wool and cellulose insulation.
When we go outside or travel to a cold climate in the winter, we put on a warm winter jacket, boots, hat, scarf, and gloves covering our entire bodies. So too must our buildings.
Principle #2: Airtight Construction
Similar to the first principle, the Passive House standard focuses on creating an airtight building envelope. Air sealing techniques throughout the home are a simple and inexpensive DIY home improvement project. Many city governments offer free air sealing "kits" for homeowners to reduce individual energy bills and municipal carbon footprints.
The Passive House standard takes airtightness to a much higher level. The standard takes extra precaution to seal all leaks around doors and windows, electrical outlets on exterior walls, sill plates, hose bibs, piping, and around recessed lights. It encourages a design with very few holes (for venting, e.g.) in the building envelope. Essentially, anywhere an air leak could occur, passive house construction will make extra efforts to plug them. It sounds complicated and expensive, but when details and materials are all reviewed and simplified from the start, it is one of the least costly principles.
Plugging air leaks helps stop heat loss, but it will also help reduce moisture accumulation or loss in cold climates. Passive homes are not only more energy-efficient than conventional homes, but they are also the most comfortable and healthy homes available. This high comfort stems from the lack of cold spots, drafts, and interior surfaces where condensation can occur. Improving indoor air quality by stopping moisture accumulation is just one way that they achieve this.
When we put on our winter jackets, we zip them up, so the wind does not blow through and remove all the heat we have produced. So too must our buildings.
Principle #3: Thermal bridge free
A thermal bridge is an area of an object with less insulation than the surrounding area. This area creates a path of least resistance for heat transfer. A useful analogy is to think of a flowing stream of water. Water will always follow the path of least resistance as it carves its way through the landscape. Similarly, the heat inside a building will always try to move toward cooler air outside the walls of a home, using the easiest path.
Imagine a well-insulated home where the building team errantly forgot to insulate a particular corner of the roof. Despite the high-performance insulation throughout the rest of the house, the heat would rush toward that defined area of least resistance. Thus, creating a thermal bridge that negatively affects the overall energy efficiency.
The studs of a house are a typical thermal bridge. A continuous layer of insulation encasing the home is one way to minimize this. Corners are a geometric thermal bridge because there is more exterior wall to draw heat out from the same interior wall area. Thus corners, bump-outs, dormers, and cantilevers are minimized.
The gap between our glove and jacket is a thermal bridge, as is the zipper, which often has an extra flap of insulation to cover it.
Principle #4: Windows, Orientation, and Shading
Windows and doors can be a significant source of heat gain or heat loss in a home. Energy Star windows are often double pane and filled with argon glass. In contrast, the Passive House standard almost always requires triple-pane windows, along with insulated frames and glass spacers and a quality installation.
Not only are the windows and doors very high-performance, but their placement is essential. Passive House buildings are optimally oriented and designed to make the most of the available natural light and heat. Solar gain through passive solar heating is strictly managed to maximize heat gain in the winter while limiting overheating during the summer. Specifically, windows with a high solar heat gain coefficient (SHGC) are placed in south-facing walls. This way, the low-angle winter sun can flood into the home, and overhangs can keep the high summer sun out. Windows with a low SHGC are often placed on east and west elevations where the heat of the rising and setting summer sun cannot be blocked by overhangs alone. Deciduous trees are beneficial for providing shade in the summer but letting the sun's warmth through in the winter when the leaves are off the trees. When we get hot in the summer, we stand in the shade, so too should our buildings.
Principle #5: Mechanical Ventilation
Some homeowners might fear that a super-insulated and very airtight home might be a recipe for unhealthy interior air quality. Yes, it is true that once we have built an airtight, thermal bridge free thermos, we can no longer breathe through the cracks in the walls. For this reason, Passive House requires the provision of continuous, filtered, fresh air and stale air removed. Most often via an efficient, silent, balanced, and commissioned Heat Recovery Ventilator or an Energy Recovery Ventilator (HRV/ERV). These devices transfer heat (and ERVs also transfer moisture) for maximum energy efficiency and healthy indoor air quality. Designers often opt for low or zero VOC building materials.
Depending on the building's climate and layout, the airtight, super-insulated building envelope home with strategically placed high-performance windows built to the Passive House standard might not need any supplemental heating. The internal gains that people, cooking, plug loads, and the sun provide may be enough.
During the summer, a heat recovery ventilator or energy recovery ventilator provides for fresh air. Simultaneously, shade, insulation, and low SHGC windows keep heat out of the home. Natural breezes and air movement can also reduce the need for mechanical air conditioning in the summer.
Most passive homes do incorporate backup mechanical heating and cooling systems for extreme temperatures. These units, however, are much smaller and simpler than in conventional buildings. The mechanical system costs less in Passive House construction.
What Is the Difference Between Passive House and Passive Solar Design?
When deep-diving into the Passive House certification, you may come across terms that are used interchangeably like "passive design," "solar design," and "passive solar design." While buildings built to Passive House standards use passive solar design principles, there is one primary difference. Passive House uses software based on physics, building science, and thermodynamics to predict the building's actual performance accurately. It uses strict performance metrics to ensure comfort and energy savings.
A home built using passive solar design can be high-performing, but results will vary. These homes can often require more active involvement from their occupants. This engagement would include the need to close windows on cold and hot days and open windows in the evening for the built-up heat to escape.
Comparison to Other Certifications
Comparing a Passive House to another certified building is like comparing apples to oranges as they are not competing but complementary. Passive House is only a performance-based energy efficiency design standard. LEED, Net Zero Energy, Living Building Challenge, Well, Zero Carbon, Pearl, and others are green or sustainable building certification programs.
LEED is a checklist-based certification program that includes eight categories of sustainability. One of these categories focuses on energy efficiency; however, it is not the primary driver of LEED-certified buildings. At the same time, LEED-certified buildings require an average energy consumption reduction of 20% or more than a reference code building. Passive House requires meeting set performance targets resulting in an 80% - 90% reduction in space heating and cooling demand. Passive House (PHI or PHIUS) certification can provide up to 48 points toward LEED certification, so it is the perfect starting point.
By its name, a Net-Zero Energy home is a home that produces as much energy as it uses within an average climate year. So, a Passive House is a perfect first step on the path to achieving net-zero and net-positive buildings as a Passive House provides a healthy indoor environment, resilience, and durability.
Of course, there are both benefits and drawbacks to each certification program. Some certifications are more appropriate than others depending on the building's location, features, and the occupants' behavior, values, and goals.
Details Matter: More on Passive House
Does a Passive House Need Heating?
A significant benefit to a Passive House is the minimal energy required to heat a home due to the insulation and tight thermal envelope. A Passive House offers resilience, even when the power goes out. Traditional homes typically require boiler or furnace systems. In contrast, Passive Houses only need a smaller and simpler system such as a ductless mini-split heat pump or electric resistance heater, depending on the climate.
Can You Open Windows in a Passive House?
In a Passive House, drafts and cold spots are nonexistent, even near windows and doors. And yes, despite the importance of maintaining a robust thermal envelope, you can open windows in a Passive House just like any other building. However, you may find that you do not need to open windows often since the indoor temperature will be very comfortable with continuous filtered fresh air year-round.
Does a Passive House Need a Ventilation System?
Yes. A driving principle behind Passive House is a healthy indoor environment. Through minimal controlled ventilation, high-quality indoor air quality can be achieved. A ventilation unit with heat recovery features is recommended to meet the requirements of a Passive House. If you live in a location with harsh weather conditions, you will undoubtedly need a ventilation system with heat recovery.
Does a Passive House Cost More?
The upfront capital cost to build a Passive House is slightly higher at 5% - 10% more than a conventional home. You will spend somewhat more on the building envelope but will save on the heating system. This upfront capital cost will often be financed in your mortgage, resulting in slightly higher monthly premiums. However, these will be offset by lowered utility costs for the 50-100+ year life of the home. This combination can mean lower monthly costs overall. In other words, a Passive House is marginally more expensive to build but less costly overall than a conventional home.
We love the simplicity and straightforward nature of the Passive House principles. They are useful and easy to understand for homeowners looking to improve their homes' energy efficiency and comfort.
Reviewed by:
Frank Crawford with Passive House Alberta, is a Professional Civil Engineer and a Certified Passive House Designer. He designed, built, and now lives since 2016 in one of the first homes built to the International Passive House Standard in Alberta, Canada. Through his work as an Energy Efficiency Consultant and the Education Committee lead of Passive House Alberta, he helps others learn how to achieve the benefits of building a highly energy-efficient building while minimizing the additional upfront costs. The benefits include increased comfort, much quieter, excellent indoor air quality, and a significant reduction in energy use and utility bills.
Article by:
Maria Saxton
Located in Roanoke, Virginia, Maria Saxton holds a Ph.D. in Environmental Design and Planning from Virginia Tech. She works as an Environmental Planner and Housing Researcher for a local firm specializing in Community Planning, Architecture, Landscape Architecture, and Historic Preservation. Her dissertation explored the environmental impacts of small-scale homes. She serves as a volunteer board member for the Tiny Home Industry Association.
