Elk Ridge Passive House Window Selection and Installation Process

This post should offer some insight into the window selection and installation process for a passive house in Montana.

“High performance vs. slim, clean lines. How can I accomplish both?”  That is how our client started their window and door selection process.

In this particular project, our clients had many performance and design elements they considered when selecting windows for this Montana passive house.  Hopefully some of the items provided below will be a great starting point on your fenestration journey.

For the Elk Ridge Passive House, the window and door selection process had two specific goals:  high thermal performance and slim, modern design. 

There are many ways to ensure your window integrates seamlessly into the airtightness layer. Choosing a vapor-open or vapor-closed wall assembly may influence the materials you select.  Products such as backer rod, sealant, vapor-open adhesive tapes, and expanding foam are just a few of the materials that can be used to ensure an airtight window installation.

WINDOW AND DOOR SELECTION

First, we considered performance:

Given that the Elk Ridge Passive House has such a large glazed area, performance was key.  Our clients knew that a triple pane curtain wall system was the ticket for their project.  Aluminum frames were selected for their slim clean lines and durable, low-maintenance black powder-coated finish

A little nerdy stuff about U-factors:

U-factor is the inverse of R-value. Generally, window manufacturers should typically provide three different types of U-factors: Ug, Uf and Uw.

The Ug refers to the performance rating of the glazing unit. The Uf refers to the performance rating of the window frame. The Uw is the performance rating of the window as a whole.  To keep it simple (and to keep this post shorter than a novel) our clients knew they needed triple pane windows to achieve the required Uw to achieve the Passive House standard.

Second, we considered the Solar Heat Gain Coefficient:

The glazing solar heat gain coefficient (SHGC) designated for a window is typically based on a number of factors: site, building orientation, and climate.

For the Elk Ridge Passive House, a high solar gain glass option was designated on the southwestern façade, yielding the largest amount of light and free heat in the wintertime.  The 5’ overhangs and external motorized shades furnish additional protection from overheating in the summer months. The above factors determine low or high solar heat gain requirements.  For example, in colder climates, the site should have good solar access along the southern axis of the home, to maximize solar gain in the winter and minimize western exposure during summer months.

Third, we considered airtightness:

Under the standards of Passivhaus Institut (PHI) the absolute limit of 0.60 air changes per hour at 50 Pascals of pressure (0.60 ACH50).  Airtight windows are paramount to a building’s envelope performance.

Equally important to the above, we needed to achieve a striking design aesthetic:

One daring (but ultimately successful) design element was the use of triple pane curved glazing at the corners to provide more daylight and create an open feel within the living spaces.  They proved challenging to trim out, though the clients were pleased with the result!

Another aesthetic choice was to insert tilt turn windows with larch frames within the aluminum curtain wall system. This added a nice design element as well as a better thermal performance to the assembly.  Although this mix-and-match approach is unconventional, it proved to be a very efficient system overall.

The clients used the beautiful, warm wood finish of the larch infill windows to counter-balance the industrial look of the concrete walls and aluminum curtain wall.  Triple pane, clear larch entry doors were selected to match this aesthetic. The wood entrance creates an inviting foyer that nicely contrasts the concrete exterior.

The final design-driven choice of a 20’ lift-and-slide door was selected for the basement family room. The generously sized door is unconventional in that it has only two wide panels of glass (typically three or four panels might be used in a door this wide).  This creates an open feel in the room with less obstructed views and creates the intentional natural lighting.  An aluminum frame was chosen for the door, given its size, material consistency, and higher weather exposure due to its location. The thermally-broken aluminum coupled with an airtight seal (high performance lift-and-slide doors are famous for good airtightness) achieves a door that performs at the desired efficiency.

WINDOW INSTALLATION

Once the Elk Ridge Passive House windows and doors were selected, it was of utmost importance to make sure they were installed correctly.  Below are the main factors considered when the passive house windows and doors were installed.

Water Tightness

Rough opening preparation and flashing is an integral component of proper window installation.  The flangeless windows of this project integrated into the drainage plane a little bit differently than would a flanged window. For long term durability, we recommend that the rough openings are prepared in a watertight manner, not just a water resistant one.  We find there are multiple options for adhesive tapes and liquid applied membranes that can adequately achieve a truly watertight rough opening.

Airtightness

There are many ways to ensure your window integrates seamlessly into the airtightness layer. Choosing a vapor-open or vapor-closed wall assembly may influence the materials you select.  Products such as backer rod, sealant, vapor-open adhesive tapes, and expanding foam are just a few of the materials that can be used to ensure an airtight window installation.

Over-insulation

Believe it or not, it is possible to improve the insulation performance of your window by up to 20%. This can be done by moving the window toward the midline of the wall assembly and adding a layer of insulation over the exterior frame of the window (“over-insulating”). There are many factors influencing where in the wall you want the windows to sit, including optimizing performance and meeting architectural design goals.

Size

Simply put, the frame is the lowest performing part of any window.  Passive House projects typically optimize glass-to-frame ratio to increase window performance and maximize daylighting.

Large, triple pane glazing units are heavy!  There are a number of different machines available that help install such large glazing units seamlessly and without damage.  Due to the steep slope at the Elk Ridge Passive House site, it was easier to use a Bailey Crane from the interior to set the glass in the curtain wall frames. This saved everyone’s back!

These are just some of the performance elements that were considered on the Elk Ridge Passive House.  Hopefully, they have given you some ideas to incorporate when considering windows and doors for high performance passive house projects.  Once you’ve chosen your windows and doors, there are a ton of factors to evaluate for a good installation plan and execution.  Selecting the right windows and doors and installing them with water and airtightness in mind has a big impact on your passive house project. 

 

 About the author: Mark Wells sits on the board of Passive House Northwest and is the Vice President of Business Development at Glo European Windows. He is based in Missoula, MT.

 

 

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