In order for VELUX to ensure the homes and buildings that feature our skylights are structurally sound and energy efficient, it's important that we follow state- and nation-wide building codes and regulations.
In California, the building codes are written into a bit of legislation called Title 24. And there are a few exceptions in there regarding skylights and other types of fenestration you'll want to make sure you're up to date on.
Skylights and Title 24
In Title 24, skylights are addressed in conjunction with other types of fenestration, like vertical windows and glass doors. It establishes rules for implementing them, as well as their labeling and certification, as they relate to
- U-factors,
- Solar heat gain coefficients (SHGCs),
- Visible transmittance, and
- Air leakage.
All of these rules for implementation are to ensure that not only is the building structurally sound, but that it's also as energy efficient as possible.
There are two ways you can be sure you're compliant with Title 24:
- The Title 24 prescriptive method, where you go through each aspect of the building, one at a time, to verify that that aspect is up to code.
- The Title 24 performance method, where the energy consumption of the entire building is considered at once by a computer program that calculates energy trade-offs to find the most cost-effective method to satisfy the Title 24 code.
What Is the Title 24 Exemption?
Title 24 actually has many exemptions built into its codes, but there's one in particular that affects fenestration and skylights that we'd like to focus on.
According to Title 24, only a certain percentage of any given building may feature fenestration - or windows or doors - on its elevations. For example: the maximum total fenestration area of a building, including west-facing skylights tilted in any direction when the pitch is less than 1:12, cannot exceed the percentage of conditioned floor area.
Additionally, the area weighted average U-factor and SHGC requirements of the initially installed fenestration products is outlined in Title 24's TABLE 150.1-A, along with Sections 110.6(a)2 and 110.6(a)3.
In these sections, Title 24 also outlines the exceptions to these codes:
- Exception #1: For each dwelling unit, up to 3 sq. ft. of new glazing area can be installed in doors and up to 3 sq. ft. of new tubular skylights with dual-pane diffusers (like VELUX's Sun Tunnel Skylights) are not required to meet the U-factor and SHGC requirements. This is equivalent to 3 separate 14" sun tunnels.
- Exception #2: For each dwelling unit, up to 16 sq. ft. of new skylight with a maximum U-factor of 0.55 and a maximum SHGC of 0.30 is allowed. These skylights can be fixed or ventilating and can be installed as
- one 4' x 4' unit OR
- two 2' x 4' units OR
- two 2' x 3' units and one 2' x 2' unit
How This Affects You
In much simpler words, these two exceptions allow you to add skylights and sun tunnels to buildings that have already reached the fenestration limit set by Title 24.
According to the first exception, you can add up to 3 square feet of new sun tunnel skylights without regard for the normal U-factor and SHGC requirements.
And the second exception says that, in existing buildings where the fenestration limit has been met, up to 16 square feet of new skylights can be installed so long as the newly installed skylights don't exceed a U-factor of 0.55 and a SHGC of 0.30. And VELUX does offer skylights that meet these restrictions.
If you're using the Title 24 prescriptive method to verify compliance, you won't need to receive approval to utilize these exceptions. However, if you're using the Title 24 performance method, you will need approval from the energy engineering group certifying the structure.
So, as you can see, these exceptions are important to know about when you're installing skylights and sun tunnels in California! If you have any questions regarding Title 24, you can find more information in the Residential Compliance Manual or by contacting your regional DSA office directly.
