Building envelope design: A next-generation Passive House window and shade connection
October 30, 2025
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Building science innovations in fenestration and shading could mean more efficient buildings
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A version of this blog first appeared as “How Passive House led us to a next generation building window connection” in Design Quarterly, Issue 25.
Building envelope design is an area that’s ripe for innovation. And I’m excited about a new window, door, and sunshade connection we have designed. It supports key aspects of Passive House building design, including simplified detailing to improve airtightness and thermal bridge mitigation.
Buildings aren’t done evolving. And building science is one area where designers are innovating.
Building science is a discipline that’s focused on building envelope design. It looks at the physics around a building and its materials. It studies how the building envelope keeps two distinct environments—most often the indoors and the outdoors, but sometimes interior spaces—separated.
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Here is a look at Passive House Design Principles: 1) high levels of insulation at walls, roofs, and floors; 2) airtight construction; 3) high-efficiency heat or energy-recovery ventilation system; 4) High-performance windows and doors; 5) passive solar design; and 6) thermal bridge mitigation.
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Targeting high-impact thermal bridges
As the Building Science Passive House Lead in North America, I’m always looking for ways we can make our buildings more energy efficient. This includes tightening up the air barrier system to reduce heat loss in the winter. “Airtight construction” is a key Passive House principle of building envelope design.
Today, we use energy modeling software to apply the Passive House principles. One key requirement is to reduce and account for building heat loss through thermal bridges. Thermal bridges are areas in a building where heat moves more easily—often found at joints, corners, or where materials meet. These spots can cause unwanted heat loss or gain. Understanding where thermal bridges occur and how they impact energy use helps us size heating and cooling systems correctly.
So, where are the high-impact thermal bridges? In my experience, the most common and largest thermal bridge is the window-to-wall transition. In a Passive House building, the window frame and glazing are highly insulated to suit a unique climate zone, which is great. The issue is how the window is positioned in the wall and how it is structurally attached to the wall.
If we find a way to lower the heat loss from our window-to-wall transitions, we can reduce the overall energy demand. The gains in energy savings here could also be used by designers to reduce insulation at other locations, which could help save dollars. Inspired by this issue, our team of building envelope consultants, facade engineers, and thermal modelers came up with a solution—Akira Window Connection.
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Connaught Triplex in Vancouver, British Columbia, where the Stantec team served as building envelope and Passive House consultant. The team used Akira Window Connection to support targeted windows and doors. (Architect: SHAPE Architecture; image courtesy of SHAPE Architecture.)
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A new window/door connection method
In modern conventional buildings, the walls are commonly designed with a continuous layer of insulation on the outside to keep heat in. But windows and doors are usually placed inside the wall opening, which means their frames do not line up with that main insulation layer.
And this leads to thermal bridging and excessive heat loss at the window perimeter. To reduce heat loss, the construction industry improved its method of aligning the window/door with the exterior insulation. Designers accomplished this by placing wood bucks at the perimeter of the rough openings and fastening continuous metal angles to the backup wall for support.
Our thermal analysis shows that even the improved conventional design still causes heat loss due to thermal bridging.
The usual way to keep transitions watertight and airtight is complicated and awkward. It involves wrapping air and moisture barrier membranes over the wood buck, then connecting them back to the window or door frame with precise folds—almost like origami. This method demands careful workmanship to avoid gaps, wrinkles (called “fish mouths”), and to keep the membrane layers properly overlapped.
Our building envelope design solution is intended to handle the vertical load and reduce heat loss—simply and elegantly. Akira Window Connection can support the weight of windows (or doors). And it nearly eliminates thermal bridging heat loss at the window-to-wall transitions.
" }Our building envelope design solution is intended to handle the vertical load and reduce heat loss—simply and elegantly.
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This method uses spaced-out thermal brackets attached to the wall structure. A horizontal angle runs along the outer edge of the brackets to support the window. This setup lines up the window frame with the exterior insulation of the wall.
We repurpose thermal brackets—usually used for siding—to support the weight of window. The system can support most of the large windows available today. This building envelope design solution gives architects more flexibility to meet performance-based energy codes.
The design’s beauty is how the window support below the sill is offset from the wall. This lets water drain out while allowing wall insulation to butt directly to the window frame. This helps prevent heat loss and makes construction easier.
We are making the window-to-wall transition simpler, speeding up construction, and boosting moisture durability while making the whole building more energy efficient. We believe all buildings that have wall assemblies with continuous exterior insulation and use punched windows/doors with rebate-style frames could use Akira Window Connection. And we’re excited to work with window and door manufacturers to integrate Akira Window Connection as the design solution their clients want.
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Akira Window Connection installed for a swing door mock-up in a mass timber wall system. The example is on display at the British Columbia Institute of Technology High Performance Building Lab in Burnaby, British Columbia.
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Next? An innovative shade design
Passive House encourages us to control solar heat gain so we can use it to passively warm our buildings or limit direct sun exposure to keep them cool. We can reduce solar gain through external shading. But standard external shades, like window-to-wall transitions, can act as high-impact thermal bridges.
Recently, I noticed that many Passive House buildings are using more external shading elements to combat overheating risks. These shades, typically made from materials such as metal, introduce high-impact thermal bridges that increase space heating/cooling demand. With shades, these buildings often can’t meet Passive House energy criteria. What can we do with our building envelope design in this situation? If we delete external shades, are we sacrificing occupant health and thermal comfort to achieve the Passive House Standard? Or do we add more insulation to the walls, roofs, and floors to counteract the heat loss borne from external shade connections?
Our design team’s solution? Akira Shade Connection. This external shading option offers climate resilience without adding heat loss. Instead of attaching external shades to the building’s wall, we attach external shades to the internal structure of the window or doorframe itself. We fasten the shade and attachment system directly to the window/door frame edges. This patent-pending shade system allows us to add external shading to the building without compromising Passive House energy criteria or occupant comfort.
Akira Shade Connection solves several building envelope issues:
- It adds external shading element without a thermal bridging penalty.
- It provides a simple way to over-insulate the window/door frame to improve thermal performance.
- It doubles as a window/door return finish. This will conceal exterior insulation edges (if applicable).
- It lowers wind-driven rain exposure at windows/doors to increase finish lifespan. It helps limit rainwater ingress.
- They are suitable for new construction, deep energy retrofits, and window replacement projects.
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Design of the Akira Shade Connection.
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We hope this will allow Passive House designers to use shading elements in their building envelope design, which will improve occupants’ comfort. The ripple effects could be significant. Passive House buildings that use external shading to control heat gain can reduce their cooling loads. This means we can downsize their mechanical cooling systems. This can reduce their associated emissions even more, while lowering construction costs.
Both Akira Window Connection and Akira Shade Connection could be game changers. These innovations can help exterior retrofit projects and new construction alike. In the end, they can make buildings more energy efficient than previously possible and with happier occupants.
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