How Many Square Feet of Skylight Can I Add Under Title 24?
It depends on the project type. A new home may have glass, skylights included, up to 20 percent of floor area. Additions use size bands with fixed square foot floors of 175, 120 or 75. A remodel can add up to 16 square feet without meeting the two area limits, but the U-factor and SHGC limits still apply.
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New home or new ADU
Total fenestration, skylights counted, is capped at 20 percent of conditioned floor area in every zone. In a 2,400 square foot house that is 480 square feet. West-facing glass is capped at 5 percent in zones 2, 4 and 6 to 15 (120 square feet here), with no limit in zones 1, 3, 5 and 16. A skylight pitched below 1:12 counts as west-facing whatever its compass direction. Separately, 16 square feet of skylight per unit may be as weak as U-0.40 and SHGC 0.30 in zones 2, 4 and 6 to 15.
Addition: find your size band
- Over 700 square feet: total glass up to the greater of 175 square feet or 20 percent of the addition's floor area, so a 1,000 square foot addition gets 200. West-facing glass up to the greater of 70 square feet or the new-home limit.
- Over 400 and up to 700 square feet: the greater of 120 square feet or 25 percent, so a 500 square foot addition gets 125. In zones 2, 4 and 6 to 15 west-facing glass is held to 60 square feet.
- 400 square feet or less: the greater of 75 square feet or 30 percent, so a 300 square foot addition gets 90, with the same 60 square foot west-facing cap.
Remodel: adding to an existing roof
An alteration that adds skylight area meets the U-factor, SHGC and area limits of Section 150.1(c)3A and Table 150.1-A. Adding up to 16 square feet is exempt from the total and west-facing area limits only, and zone 15 uses an SHGC of 0.23.
How the area is measured
Skylight area is the rough opening, and a skylight is fenestration on a roof less than 60 degrees from the horizontal. A steeper glazed unit is a window in a wall.
Glass specifications are on skylight requirements and ADU skylights. Related: room additions, skylight replacement, skylight shaft insulation and our residential reports.
Common Title 24 Questions
- When is Title 24 required for a home?
- Does a remodel need Title 24?
- Does a room addition need Title 24?
- What plans are needed for a residential Title 24 report?
- How much does a residential Title 24 report cost?
- How long does a residential Title 24 report take?
Frequently Asked Questions
No. It is the amount a remodel can add without meeting the total and west-facing area limits. New-home skylights count inside the 20 percent total.
It has its own: up to 3 square feet with a dual-pane diffuser per dwelling unit is excused from the table U-factor and SHGC.
Explore Skylights
- Skylight Replacement: Title 24 Requirements
- Skylight Shaft Insulation: What Title 24 Expects Around the Light Well
- Solar Tubes (Tubular Daylighting Devices): Title 24 Rules
- Title 24 Skylight Requirements for Homes
View all Skylights guides → · Windows and Building Envelope · Title 24 guide