Are Double-Pane and Low-E Windows Required in California?
No law names a glass type. Part 6 sets performance numbers: a mandatory weighted-average U-factor of 0.40 for new construction, and prescriptive limits of 0.27 or 0.30 with SHGC caps in most zones. In practice those numbers mean double glazing with a low-e coating. Windows you are not replacing carry no requirement.
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Numbers, not materials
The 2025 Standards contain no sentence requiring low-e coatings, argon or two panes. They set performance. Section 150.0(q) gives new homes and additions a weighted-average U-factor ceiling of 0.40. The prescriptive path in Section 150.1(c)3A and Table 150.1-A is tighter: 0.27 in zones 1 to 5, 11 to 14 and 16, and 0.30 in the rest, with an SHGC of 0.23 in zones 2, 4 and 6 to 14 and 0.20 in zone 15.
What those numbers mean in glass
The compliance manual is plain about it: windows that satisfy the prescriptive requirements are likely to have at least double glazing, a low-emissivity coating and argon gas fill with an improved spacer. Two panes laminated together are not double pane. Low-e cuts the center-of-glass U-factor but does nothing for losses through the frame.
Why a bare window with no label rarely works
Windows without a rating take values from the default tables, and the manual says no product in those tables meets the 0.40 maximum by itself. An unlabeled window can pass only if it is averaged with better products or traded off in a performance report. See NFRC labels.
Where single pane can legally stay
- Existing windows you do not replace, since an alteration reaches only the altered component.
- New glass in an existing sash and frame is a repair if it performs at least as well as the original.
- Up to 75 square feet of vertical replacement may use U 0.40, with SHGC 0.35 in zones 2, 4 and 6 to 15 and 0.23 in zone 15.
- In new construction, up to 10 square feet or 0.5 percent of floor area is exempt from the 0.40 cap, and buildings under the Wildland-Urban Interface code are excepted from it.
Choosing the coating by climate
Low-solar-gain coatings usually give an SHGC of 0.40 or less and cut cooling load. High-solar-gain coatings keep solar heat for heating climates.
Read which number matters, windows under Title 24 and the single-pane remodel answer. We prepare residential reports from your window schedule.
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. The Standards do not mention it. The manual only expects compliant windows to commonly include it, alongside low-e coatings and an improved spacer.
Usually yes if you are not replacing them, because only the altered component must comply. Replacing them brings the U-factor and SHGC limits or an exception.
Explore U-Factor and SHGC
- Dynamic Glass and Electrochromic Windows Under Title 24
- Mixing Window Types: How the Area-Weighted Average Works and What to Do When One Misses
- Title 24 U-Factor vs SHGC: Which Number Matters?
- Where Window U-Factor and SHGC Appear: CF1R, Plan Set, Label and Installer Certificate
View all U-Factor and SHGC guides → · Windows and Building Envelope · Title 24 guide