As discussed in a previous post, California instituted new lighting standards under Title 24, specifically regarding lighting controls and energy efficiency. This post explores the idea of “daylighting” in Title 24 and what this means for you.
Daylighting is the controlled admission of natural light into a building. Glass doors, skylights, and windows (a.k.a. “fenestration”) all have a significant impact on building energy efficiency. These points of entrance and exit impact both heating and cooling. For example, if you have an A/C, a window is a point where the cold air could leak. Additionally, skylights allow in sunlight which increases the heat in your building. As such, the size, location, and operation of these areas dramatically affect energy consumption.
There are three types of fenestration listed under Title 24:
- Manufactured refers to windows and doors that are built in a factory. Manufactured windows represent the majority of fenestration utilized in buildings
- Site-Built is any fenestration assembled on site using factory-cut or factory-formed units. Site-built fenestration is often used in non-residential buildings
- Field Fabricated refers to any fenestration that is entirely built on site and utilizes materials not intended for use as fenestration
U-Factor and SHGC Ratings
U-Factor measures the rate of heat loss through a window. The SHGC (or “Solar Heat Gain Coefficient”) measures how well the window blocks heat. These two measurements determine the energy efficiency of your skylight.
Changes to Title 24
In 2013, Title 24 energy standards were updated. Mostly, the U-Factor or rate of heat loss was reduced for all three types of fenestration. Though the compliance standards are stricter, you can still gain compliance credit with high-performance windows. For example, if you choose a window with an SHGC (the amount of solar radiation admitted through a window) of 0.25 or lower, the less your AC unit will have to work to keep the area cool, thus descreasing your overall energy consumption. Multiply this by all windows in your building, and overall the building energy efficiency will increase greatly.
What affects performance?
Design, the location of the window, materials used in the frame and glass, and the configuration of the glass all affect window performance. If you want to maximize energy efficiency, vinyl and wood are better insulators than metal which makes them ideal for frames. Additionally, the number of glass panes, the coating, and glazes used all affect the SHGC rating. By paying attention to the specific materials you use to create fenestrations, this can help you stay compliant within the energy efficiency standard.
In short, pay attention to:
- Window types
- The gap width of the panes
- The material used to separate multiple panes of glass
There are opportunities throughout the entire process of constructing and assembling the window to improve its performance.
Special Tricks with Shading
Shade plays a big part in lowering energy use, as well. Shades can be installed to shield the window and help keep areas cooler. But take note: According to Title 24, the designer and builder have specific requirements to control the shading device per new lighting standards and building codes. These requirements are set to ensure that the shading device operates and is installed correctly – especially if you want compliance credits for installation.
If you are in a smaller non-residential building, a great designer trick is to install overhangs positioned above the windows, especially those that face south. Ideally, the overhang will provide shade during the summer months when the building will be operating on air conditioning heavily, which can help stay compliant within the energy efficiency standards.
However, shading is significantly more difficult for the west and east facing sides of a building. The sun rises in the east and sets in the west, so when it strikes these windows it is low in the sky. Overhangs are insufficient. You can try using vertical fins; however, these installations degrade the view and obscure the natural light that passes through the window.
In these situations, it is worth considering landscaping features to overcome the heating problem, such as tall trees. You are ineligible for the compliance credits, but you overcome the low-sky sun in the late afternoon while staying more energy efficient in regards to internal temperature control within the building.
If you would like more information, we are continually updating our blog with information regarding the latest regulatory and statutory updates. Check out our latest posts covering the basics of Title 24, achieving Zero Net Energy, new lighting standards, and guidelines for lighting controls.