How to Choose Performance Window Shade Fabric
Updated: Nov 25, 2020
Among the millions of decisions made in designing a building, the material for window coverings is probably not the most pressing matter for architects. However, when it comes to creating sustainable designs, the material of your window shade fabric drastically affects occupants' experience inside your building- not just aesthetically, but physically, performatively, and even financially.
As natural daylighting system designers, our choice in window treatments stems from a multitude of factors that are frequently overlooked but crucial to meeting the design intent of the building. In this article, we're going to show you how window shades' different material factors can define:
The amount of natural daylight in your space
The severity of glare experienced by occupants
The thermal comfort of your space
The level of privacy for occupants
The visibility and connection to the outside
START WITH DESIGN INTENT
It's no news to an architect that you must start any design with the end in mind. Where is the designed space? Who will use it, and how? What design standards and building codes do I need to meet? These are the same questions you should start with when choosing your performance shade fabrics.
For example, when designing an open office with south-facing windows, the shade fabric must address the heat gain and glare coming from the sun and any reflective surroundings to ensure physical and visual comfort for employees. Knowing natural light is the #1 desired office perks for employees, the fabric should also allow an adequate amount of daylight coming through while maintaining a view to the outside. How do you pick the perfect solution out of thousands of shade fabric options available in the marketplace?
RELEASE THE RAT
No, we're not talking about rodents. The RAT Equation is the summation of the Reflectance (Rs), Absorption (As), and Transmittance (Ts) of solar energy through an opening. These factors affect how much heat an opening takes in, how bright it is, and how much glare will be experienced by occupants. Here we see each element in action:
When deciding upon a window shade fabric, the RAT Equation should be your starting point. However, many make the mistake of only looking at the RAT values of the fabrics and ignore the impact of the glazing type on the actual performance. As natural daylighting designers, we can help architects look at the fenestration as a combination fabric and glazing system to evaluate the true performance improvement.
Window treatments are available in a series of different opacities, referred to as the openness factor. Based on a scale of 1 to 100, the fabric's openness factor defines what percentage of transparency is present. For example, if a fabric has an openness factor of 10%, that means that 90% of visibility is blocked out, with 10% of light coming through.
The standard values are 10%, 5%, 3%, 1%, and 0%, but varying percentages exist outside of this range. Here we will see the influence of openness factors on the amount of light coming into a space and the visibility to the outside:
The openness factor of window treatments has far-reaching implications that extend to financial impacts for both the occupants and building owners. Everything about an interior space can be meticulously curated to occupants, but if they aren't getting the quality daylight they need to use the space properly, occupants will turn to electric light- driving up energy consumption while not getting the best quality light. Not mitigating glare and heat gain can lead to decreased productivity for occupants and higher HVAC costs for building owners.
While the color of a window treatment is typically considered a stylistic choice, it's actually a decision with a much broader impact than just the visual design. Fabric color affects the reflectance of solar energy, the amount of glare, the privacy of occupants, and the visibility they have to the exterior.
When it comes to reflectance, lighter fabrics reflect light and heat from openings while darker fabrics absorb the energy. For openings facing a more intense sun throughout the day, a lighter fabric will drastically help cool the space by reflecting the heat away. However, lighter fabrics will bring the illumination of the sun into the interior, possibly creating a bright glare when the interior lighting is imbalanced. In contrast, dark fabrics will dampen the light significantly.
Privacy and visibility are also affected by the color of the fabric. Lighter fabrics are harder to see through, making them the more private of the translucent fabric options. Darker fabrics, however, allow a higher level of visibility to the exterior with slightly reduced privacy. Here, we see the examples of a 5% openness factor shade in light and dark, and their effect on exterior visibility and privacy:
MAKE IT GREEN
After you have considered the different factors that play into making a decision on your shade fabric, it's time to dive into the composition of the shade fabric material. Choosing the right fabric materials to avoid harmful composition, like PVC, can help your project achieve green building standards, such as LEED, WELL, and the Living Building Challenge.
Of course, it takes more than just choosing the right fabric to select the best window shade system for your projects. Many factors, especially the control of your shade systems, play a large part in designing green and sustainable window shade solutions. Automated and integrated window shade systems can further your effort in achieving LEED standards, including contribution to the following categories:
DESIGNING A BETTER BRIGHTER FUTURE
The careful consideration of all these factors is imperative to the discovery of the perfect shade fabric and system for your interior space. The right fabric will perfectly balance the need for natural light, views to the outside, style, and heat gain and glare mitigation. It's not just about blocking the sun, but how you use it to further your design intent.