Windows installed in California must meet the California Building Standards Code (Title 24), which sets rules for emergency escape openings, child fall protection, safety glazing in hazardous locations, thermal performance by climate zone, and flashed installation. The California building code window requirements changed on January 1, 2026, when the 2025 Energy Code took effect for all new permit applications and tightened U-Factor limits in many of the state’s 16 climate zones.1California Energy Commission. 2025 Building Energy Efficiency Standards Most replacement work is covered too, not just new construction.
Egress Windows in Bedrooms and Basements
Every sleeping room and every basement with habitable space needs at least one window an occupant can climb out of, or a firefighter can climb into. The California Residential Code sets four minimums that all apply at once:2City of East Palo Alto. Residential Emergency Egress Windows Worksheet
- Net clear opening area of at least 5.7 square feet (5.0 square feet is allowed for grade-level windows that open directly outside)
- Clear opening height of at least 24 inches
- Clear opening width of at least 20 inches
- Sill no more than 44 inches above the finished floor
The area requirement is the one people miss. A window built to the bare 24-by-20-inch minimums produces only about 3.3 square feet, well short of 5.7. One dimension has to run substantially larger than its minimum for the opening to qualify. Measurements are taken with the sash fully open and screens removed.
Bars, grilles, or security grates over an egress window have to release from the inside without keys, tools, or special knowledge. Anything that could slow a panicked exit fails inspection.
Fall Protection for Operable Windows
A separate rule protects children from falling out. When an operable window sits more than 72 inches above the exterior grade below it, the lowest point of the clear opening must be at least 24 inches above the interior finished floor. For any window opening within 24 inches of the floor, the operable portion cannot allow a four-inch-diameter sphere to pass through.3Tuolumne County. Residential Egress Windows
Most windows meet this by geometry alone. When they don’t, you have two options. Install a window opening control device that limits the initial opening to four inches but includes an emergency release allowing the window to open fully for escape, or install a window guard or fall prevention screen. Either device must meet ASTM F2090, which covers fall prevention for children five and younger while preserving egress.4ASTM International. Standard Specification for Window Fall Prevention Devices With Emergency Escape (Egress) Release Mechanisms F2090-21
The emergency release must operate without keys, tools, or excessive force. A device that blocks a child from falling out but stops an adult from escaping a fire defeats the point of having an egress window in the room.
Where Safety Glazing Is Required
Certain window locations put glass in the path of people who might walk or fall into it, and the code requires tempered or laminated safety glazing in those spots:5Humboldt County. Guards and Window Fall Protection CRC R3
- Glazing within a 24-inch arc of either vertical edge of a door, when the bottom edge is less than 60 inches above the walking surface
- Glazing within 60 inches, measured horizontally and vertically, of a bathtub or shower drain inlet
- Fixed or operable panels with a bottom edge less than 18 inches above the floor and a top edge more than 36 inches above the floor
- Glass along stairways, landings, and ramps where the bottom edge is less than 60 inches above the walking surface
Safety glazing carries a permanent etched marking in a corner identifying the manufacturer, the glass type, and the applicable standard. Inspectors look for this stamp. When you replace glass in any of the locations above, the replacement must be safety glazed even if the original wasn’t. California Health and Safety Code Section 25997 backs this up for all glazing replaced in hazardous locations.
Energy Performance Under Title 24
Title 24, Part 6 controls how much heat a window loses and how much solar radiation it lets through. Two ratings do most of the work: U-Factor (heat loss through the assembly) and Solar Heat Gain Coefficient, or SHGC (solar radiation transmitted inside). Lower numbers are better on both.
New Construction After January 1, 2026
The 2025 Energy Code applies to permit applications filed on or after January 1, 2026.1California Energy Commission. 2025 Building Energy Efficiency Standards The previous 2022 cycle set a 0.30 maximum prescriptive U-Factor statewide. The 2025 code drops that to 0.27 in many cooler and inland climate zones while holding 0.30 in the rest. SHGC still applies in warmer zones and generally caps at 0.23, though projects can use the performance compliance path to trade off between building components.
California’s 16 climate zones run from the foggy coast to inland desert, and the requirements shift accordingly.6California Energy Commission. Climate Zone Tool, Maps, and Information Cooler zones (1, 3, 5, and 16 among them) have no prescriptive SHGC limit because blocking solar heat there works against you. Warmer zones enforce SHGC strictly.
Replacement Windows
Swapping windows in an existing home gets a more relaxed prescriptive standard up to a point. For up to 75 square feet of window replacement, the maximum U-Factor is 0.40 and maximum SHGC is 0.35 in applicable zones. Cross the 75-square-foot threshold, or add entirely new windows where none existed, and the tighter new-construction numbers apply.7Napa County. Windows, Skylights, and Other Fenestration – Guide to Energy Code Requirements
Substantially expanding total window area typically forces you onto the performance compliance path, which uses a computer energy model. That usually means hiring an energy consultant or HERS rater to run the calculation and produce the required documentation.
NFRC Labels
Every new or replacement window has to carry a National Fenestration Rating Council (NFRC) label certifying its U-Factor, SHGC, visible transmittance, and air leakage.8California Energy Commission. Building Energy Efficiency Standards Inspectors check for these labels at final inspection. A window without one can fail even if it would have met the numeric requirements.
Flashing, Fasteners, and Air Sealing
A code-compliant window still fails if it isn’t installed to shed water. The California Residential Code requires approved corrosion-resistant flashing installed in a shingle pattern around the full window perimeter and integrated with the water-resistive barrier behind the siding, so any water reaching the assembly drains outward rather than into the wall.
Pan flashing at the sill is mandatory. It’s a tray that catches whatever gets past the weather seal and sends it back outside before it hits framing. Leaving pan flashing out is a common installation mistake, and inspectors look for it.
Manufacturer instructions govern fastener type and spacing when the manufacturer provides them. Absent that, the industry baseline is minimum 6d fasteners no more than 16 inches apart, with a fastener within 10 inches of each corner but no closer than 3 inches to the corner itself. Air sealing the gap between the window frame and the rough opening is required as well, both for moisture control and to prevent energy loss through infiltration.
When You Need a Permit
Whether a permit is required depends on scope. Replacing glass within an existing frame, or dropping a vinyl insert into an existing frame without disturbing the weather seal, is generally treated as maintenance and needs no permit. Removing the whole window including its frame, replacing flashing, changing the opening size, or cutting a new opening requires a permit.
Skipping a required permit tends to be more expensive than pulling one. Unpermitted work can surface during a home sale, force a bring-to-current-code correction, or leave a homeowner without insurance coverage if a bad installation causes water damage.
Permitted projects get at least one inspection, typically after installation but before interior trim goes on, so the inspector can verify flashing, fastening, air sealing, and the NFRC label. Scheduling the inspection at the right stage of the job avoids tearing off finished trim later.
Lead-Safe Rules for Homes Built Before 1978
Window replacement in any pre-1978 home triggers the EPA’s Renovation, Repair, and Painting (RRP) rule on top of the California code. The contractor must be a certified renovation firm, and at least one worker on site must be a certified renovator who has completed EPA-accredited training.9US EPA. Renovation, Repair and Painting Program – Firm Certification California does not run its own version of this program, so the federal rules apply directly.
Before any old window comes out, the work area has to be contained with plastic sheeting extending at least six feet in every direction for interior work, and at least ten feet for exterior work. Warning signs go up, and HVAC ducts in the work area get sealed to keep lead dust from circulating.
After the work is done, the certified renovator cleans with HEPA vacuuming and wet wiping, then performs a cleaning verification on every window sill in the work area using disposable cloths compared against a standardized card. Contractors who skip these steps face fines of up to $37,500 per day per violation.
The Federal Window Tax Credit No Longer Applies
The Section 25C energy efficient home improvement tax credit, which covered 30% of the product cost up to $600 per year for qualifying windows, is no longer available for new work.10Internal Revenue Service. Energy Efficient Home Improvement Credit Federal legislation terminated the credit for any property placed in service after December 31, 2025.11Internal Revenue Service. FAQs for Modification of Sections 25C, 25D, 25E, 30C, 30D, 45L, 45W, and 179D Windows installed in 2025 or earlier can still be claimed on the applicable return. Windows installed in 2026 or later do not qualify for the federal credit.