I recently experienced firsthand a Passive House Institute (PHI) certified home, 17 Mile Haus, located in Pacific Grove, California. I was invited to tour the home by the architect, Bronwyn Barry, CPHD, RA. Her creative design accentuates views and access to nature, while creating a well-lit and comfortable indoor thermal environment. The house debunks several myths associated with Passive House design.
In this blog, I highlight four of these myths and use this house’s design, along with larger non-residential building projects, to demonstrate how misleading these myths are.
Before doing any debunking, let me first introduce Barry and then review some Passive House design basics. Barry runs her own architectural design practice, Passive House BB, in San Francisco and has won several awards for her Passive House architecture. She is a founder of the Passive House Network (PHN) and Passive House California. She volunteers as PHN’s policy director, supporting local, state and national efforts to scale Passive House implementation.
Passive House Basics
Passive House is a design strategy that strives to minimize energy use and create comfortable interior environments by employing highly insulating, air-tight building envelopes, utilizing passive solar gains to supply heating where possible and minimizing them to prevent overheating. Ensuring adequate ventilation is critical with air-tight building envelopes. For this reason, high-efficiency heat recovery ventilation is typically used, with a preference for natural ventilation where possible.
Two organizations certify Passive House designs.
- PHI is an international organization based in Germany. It offers Classic, Plus and Premium certifications for new builds and EnerPHit versions for retrofits. This is the organization that certified 17 Mile Haus. PHN is the United States-based affiliate of PHI; and
- Phius, a U.S.-based organization that offers Phius CORE, Phius ZERO for net-zero performance and Phius REVIVE for retrofits.
Both Passive House approaches result in highly energy-efficient buildings. Both can be applied to any type of building, including single-family homes, multi-family residential and non-residential buildings.
Myth 1: Passive House Designs Have Less Glass
The windows and doors in 17 Mile Haus are large and selectively positioned to minimize heat gain while framing the views of the trees outside. It features a large 12-feet-high-by-16-feet-wide, lift-and-slide, triple-glazed, aluminum-clad wood door on the south elevation (see Figure 3). The door provides a dramatic statement and connection to the outside patio, allowing inside-outside living.
Similarly, a tall in-swing, French door with fixed side panel was implemented on the adjacent southwest elevation and also in the ground floor owners’ bedroom (see Figure 6). A mixture of tilt-turn operable and fixed triple-pane wood windows was installed elsewhere. These windows and doors were all manufactured in Kansas by Advantage Architectural Woodwork, although the insulating glass was sourced from Europe.
Barry asserts that Passive House design allows architects to make smarter choices about window size and placement. Typically, Barry inputs her concept designs with initial window and glazed door placements into the Passive House Planning Package (PHPP), the design tool for PHI certification, and uses that to optimize her design. The PHPP package, she says, “provides a fantastic output graphic that shows the heat gain and heat loss through each window on each orientation” based on the local climate inputs. She uses those outputs, iteratively moving and resizing windows and glazed doors, to optimize the total heat gains and losses, dialing in her design by dialing in the windows.
The PHPP requires inputs of:
- frame profile (height, width and depth);
- frame and center-of-glass U-factors;
- thermal conductance of the spacer system and its connection to the frame (psi-value);
- solar heat gain coefficient of the glass; and
- window size.
Because the PHPP separates frame from glass effects, the thermal conductance and heat gain used in the calculation change with window size and shape.
Since frame and edge-of-glass thermal performance is typically worse than the center of glass, optimized Passive House designs tend towards fewer, but significantly larger, windows and glazed doors to minimize edge effects. From a glazing perspective, this means at least as much, if not more, glass is being used, but within fewer window units. Almost every window in this house was a different size, and the total fenestration area was approximately 550 square feet.
In comparison, windows in a similarly sized typical U.S. colonial-style house would have a lot more size uniformity, with an upper estimate of window area of about 450 square feet (30 windows of 36 inches wide by 60 inches high). In addition, there is much less use of muntin bars and mulled windows in Passive House designs because these strategies drive increased thermal conduction. Otherwise, there is a similar variety of design offered in Passive House to standard residential construction.
Myth 2: You Can’t Open Doors and Windows in a Passive House
People think an air-tight building means the building needs to be closed all the time, with no windows or doors allowed to be open. Nothing could be further from the truth. Seventeen Mile Haus debunks the myth with its many large patio doors that are meant to be opened and left open when the weather allows, to create an open-to-nature space. This feature has not reduced the outstanding energy performance of this home (see below).
Passive House design controls unintentional air leakage to reduce heat loss and gain through uncontrolled leakage paths. Barry prefers to refer to Passive House design as “smoke-tight,” not “air-tight,” as this seems to better convey the design intent. When the windows and doors are closed, smoke from wildfires will not be able to leak through the envelope.
Myth 3: Passive House Design Results in Poorly Daylit Interiors
Anyone walking into 17 Mile Haus would challenge this assumption. The multiple double-height patio doors make the space feel light and airy and deceptively large for a 2,800-square-foot, three-bedroom house.
Barry notes that Passive House designs have no more limitations on daylighting than a typical building design. In her experience, Passive House highlights more daylighting options because the designer has a better understanding of the building physics and constraints. Fewer muntin bars and higher glass-to-frame ratios also improve the effective visible light transmission in Passive House designs.
Barry asserts that there are also lots of passive design opportunities to help improve daylighting, which are not envelope-related. She shared a daylighting approach she often employs: using internal windows (either with diffusing or clear glass) to transfer daylight from one room to another. It allows light to be transmitted into a room from multiple sides, which balances the daylight and reduces glare (see Figure 5).
Comfortable daylight is critical. Barry identified the east and west façades as making or breaking a design because of the low-angle, high-intensity sun penetration that drives overheating and glare. Typically, the strategy is to minimize glazing on those elevations, but in some locations, especially on the North American West Coast, the west is where the views are and where glass is desired.
On those western orientations, she employs a strategy of framing select views and managing heat gain and glare with exterior shading. For example, she uses solar-actuated exterior blinds since overhangs are not effective. Barry notes that by clearly highlighting the challenges, Passive House design helps the architect understand the dynamics of the problem and its constraints. In doing so, it supports more creative problem-solving.
Myth 4: Passive House Certified Buildings are More Expensive Than Code-Minimum Designs
Barry asserts that the cost of building a PHI-certified project is directly linked to the experience of the designer rather than the inherent cost of materials and construction. Experienced Passive House designers have learned techniques and value-engineering strategies to keep costs down. They use the PHPP as a design tool from the beginning of the design process to optimize the design, not as a “compliance check,” which allows for more effective cost-optimization. According to Barry, novices often misinterpret Passive House as a checklist compliance system, rather than as a design tool. As a result, they miss cost-optimization opportunities.
That experience is the key to lowering Passive House costs, as borne out in the report Barry wrote for PHN using costs from sixteen multi-family buildings in New York City designed by a variety of firms with and without previous Passive House design experience.
Barry’s home designs typically cost the same as or less than similar code-minimum homes in California. She attributes this to her experience and ability to employ cost-effective design and specification strategies.
She also described the Hotel Marcel Passive House (EnerPHit certified) office-to-hotel conversion in New Haven, Connecticut. Here, the PHPP was used as a value-engineering tool, resulting in a cost of construction that was less than a code-minimum hotel. Window optimization was a huge part of being able to gain approval from the historic preservation board and make the project financially viable.
Additionally, Barry mentioned that increased costs are typically incurred if a designer is not tasked with achieving Passive House performance from the outset. In this case, a regular design must be “shoe-horned” into the Passive House process. This can result in significant costs to remedy design choices not optimized for the Passive House. It is much more cost-effective to achieve Passive House when you start with that end goal in mind, no matter whether the project is new construction or a retrofit.
17 Mile Haus Performance: 5th Myth Busted?
As built and operated, 17 Mile Haus has a measured energy use intensity (EUI) that is only 0.3% different from that predicted by the PHPP model. An impressive correlation. Barry told me this degree of agreement is not atypical of PHI-certified buildings. This stands in stark contrast to the performance gap between as-designed and as-built identified for regular code-minimum buildings.
Barry’s collaborator, Megan Ring, has analyzed publicly available utility data (from PG&E) using her PassivSure tool. The findings show this house’s energy consumption is 87% better than similarly sized homes in the same zip code (see Figure 7). So perhaps this is another myth busted? High thermal performance envelopes are indeed impactful in milder California climates.
Takeaways
While some Passive House designs can look quite different from typical U.S. buildings, they don’t have to. Nor do they use less glass or are less well daylit. Window size and performance are better optimized by elevation, mostly resulting in fewer, less complex (no muntins, not mulled), but significantly larger windows. However, typically, the fenestration used has much higher thermal performance (triple-pane, thermally broken frames, warm-edge spacer) than U.S. code-minimum fenestration.
Despite the higher value-added fenestration, Passive House designs are not necessarily more expensive if designed by an experienced Passive House architect.