Skylight Replacement in California: Timing, Flashing, Glazing and Title 24

Skylights fail differently from windows and are replaced differently. This guide is part of our California window guide. If you are deciding between a skylight and a tubular device, see our sibling guide on skylights versus solar tubes.

When a skylight needs replacing

• Fog or haze between the panes. The insulated glass seal has failed. It will not clear, and the unit has lost insulating performance. The cause is the same as in a window; see why windows fog between the panes.
• A yellowed, crazed or cracked plastic dome. Acrylic and polycarbonate domes degrade in sunlight. Once brittle, they crack under hail, a fallen branch or foot pressure.
• Leaks you have already patched. Roofing cement around a skylight is a temporary repair. Repeated patching means the flashing has failed.
• Stains or soft drywall in the light shaft. Evidence of leaks or long-term condensation.
• A venting skylight that no longer opens or closes fully. A skylight that will not close is an emergency before the first storm.
• Age. VELUX states that its skylights can last 20 to 30 years and suggests updating after about 30 even without a visible problem.
• Single glazing or a clear dome over a hot room. Old skylights are often the largest source of summer heat gain in the house.

VELUX lists discoloration from sunlight, mildew stains from moisture, leaks and condensation around the panes as signs that an old bubble skylight is due.

When it does not

A dry, clear skylight with intact flashing does not need replacing because of its age alone. Condensation on the room side of the glass on winter mornings is an indoor humidity problem, more common in bathrooms and kitchens, and a new skylight will only partly cure it. Run the exhaust fan and see our page on fighting condensation.

Curb-mounted and deck-mounted

These are the two main ways a skylight attaches to a roof, and which you have largely decides what you can replace it with.

VELUX also sells self-flashed units with the flashing built in, which it lists for flat or low-slope roofs. Pitch ranges are product-specific. VELUX lists its deck-mounted fixed skylight as suitable for roof pitches of 14 to 85 degrees and its curb-mounted solar-powered model for 0 to 60 degrees. Check the range for the exact model against your roof.

The code addresses low slopes too. Section R324.6.8 of the 2025 California Residential Code requires unit skylights on roofs with a pitch of less than 3 units vertical in 12 horizontal to be mounted on a curb extending at least 4 inches above the roof plane, unless the manufacturer's installation instructions specify otherwise.

Many California tract houses from the 1970s through the 1990s have acrylic domes on site-built curbs. Those are the easiest replacements: a curb-mounted glass unit is ordered to the curb's outside dimensions. Converting from curb to deck mount is possible during a reroof, when the curb can be removed and the opening reframed.

Flashing is the job

Skylights have a reputation for leaking. Most of it traces to flashing that was improvised on site, relied on sealant, or was disturbed during a later reroof. The skylight unit is rarely the leak.

Manufacturers now sell engineered flashing kits matched to the mount type and the roofing material. VELUX, for example, lists separate kits for asphalt shingle, metal and tile roofs, with the tile kits including risers to accommodate tile height. It describes three layers of water protection on its skylights: a deck seal or gasket, an adhesive underlayment wrapped over it, and the flashing as the final layer.

What to ask for:

• The manufacturer's flashing kit for your roofing type, not site-bent metal and mastic.
• Self-adhered underlayment wrapped up the sides of the unit or curb and lapped correctly with the roof underlayment.
• Step flashing woven into the courses on shingle and tile roofs, so water is shed at every course.
• No reliance on exposed sealant. Sealant on a roof has a short life in California sun.

Warranty terms follow the flashing. VELUX states that its deck- and curb-mounted skylights carry a 10-year installation warranty, plus 20 years on glass, 10 years on product and 5 years on blinds and controls. Ask the installer which flashing is being used and whether the installation qualifies for the manufacturer's leak coverage. A site-built flashing may leave you with product coverage only.

Glazing safety: CRC Section R324.6

The 2025 California Residential Code regulates skylight glass in Section R324.6, skylights and sloped glazing (in the 2022 code these rules were under R308.6). Glass overhead is treated differently from glass in a wall because broken pieces fall on people.

Permitted materials under R324.6.2 are limited to:

• Laminated glass with a polyvinyl butyral interlayer of at least 0.015 inch for panes of 16 square feet or less whose highest point is no more than 12 feet above a walking surface, and at least 0.030 inch for larger or higher panes
• Fully tempered glass
• Heat-strengthened glass
• Wired glass
• Approved rigid plastics

Retention screens. Where the pane facing the room is fully tempered, heat-strengthened or wired glass, the code requires a broken-glass retention screen below it, with exceptions. No screen is required where laminated glass is the single glazing or the inboard pane. No screen is required for fully tempered glass where the glass area is 16 square feet or less, the highest point is no more than 12 feet above a walking surface, the glass is no more than 3/16 inch thick and, in multiple glazing, the other panes are tempered, laminated or wired. A second exception covers steeply sloped glass close to the floor.

In practice: typical residential skylights with tempered glass in ordinary ceilings meet the exception. In a room with a high or vaulted ceiling where the skylight sits more than 12 feet above the floor, the simplest way to comply is laminated glass as the inboard pane. Laminated glass stays in the frame when it cracks, so it is the better choice above beds, stairs and seating in any case.

Labeling. Under R324.6.9, unit skylights and tubular daylighting devices must be tested by an approved independent laboratory and bear a label identifying the manufacturer, performance grade rating and inspection agency. A factory-built skylight has it. A site-glazed assembly made from loose glass does not.

Title 24: skylights have their own numbers

The Energy Code defines a skylight as fenestration installed on a roof less than 60 degrees from horizontal. It is rated with the same two values as a window, U-factor and SHGC, on an NFRC label. The requirements differ from those for windows.

So the figure to check on a replacement skylight is 0.40 and 0.30, not the 0.27 and 0.23 quoted for windows. Current glass skylights with low-e coatings and argon generally meet it. A single-layer clear dome is unlikely to, so check the label before assuming a like-for-like dome replacement will pass.

Sixteen square feet is roughly two skylights of two feet by four feet. Beyond that, added skylights have to meet the standard window values or the project moves to the performance approach. Our page on Title 24 for replacement windows explains climate zones and compliance paths, and how to read an NFRC label explains the label.

In fire hazard severity zones, skylights also have to meet California's Wildland-Urban Interface Code. Ask the manufacturer whether the unit you are considering is approved for those zones. See wildfire-resistant exteriors.

Timing with a roof replacement

Skylight flashing is interleaved with the roofing. That makes the reroof the natural time to replace skylights, for four reasons:

1. The roof is already open. The labor to remove and reflash around the skylight is being spent either way.
2. Tear-off is rough on old units. Prying up roofing around a decades-old skylight can break seals and crack brittle domes.
3. Warranties line up. VELUX notes that replacing skylights with the roof synchronizes the skylight and roofing warranties.
4. You avoid cutting into a new roof. Replacing a skylight five years into a new roof means disturbing new roofing and its warranty.

If you are reroofing and the skylights are more than about fifteen years old, plastic, or have any history of leaks, replace them with the roof. If the skylights have failed and the roof has years left, a competent installer can replace the skylight alone by removing and relaying the surrounding roofing; it is done routinely on shingle roofs and takes more care on tile and metal.

The reroof is also the time to decide whether you want the skylight at all. An opening can be framed in and roofed over, and for a skylight that overheats a room that is sometimes the right answer.

Venting skylights

A skylight that opens lets hot air out at the highest point of the room, which is useful in bathrooms, kitchens, stairwells and upper floors without air conditioning. Under the Residential Code's natural ventilation provision, openable skylights are among the openings that count toward a room's required ventilation area.

• Manual units open with a crank or pole and suit skylights within reach.
• Electric units are wired to house power and controlled by a switch or remote.
• Solar-powered units need no wiring, which makes them practical as replacements. VELUX describes a small exterior solar panel that charges a concealed battery, and a built-in rain sensor that closes the skylight automatically at the first sign of rain.

Venting units have more seals and moving parts than fixed ones, so use fixed skylights where you only want light. Blinds are worth considering on any skylight over a bedroom or a west-facing roof; they are easier to add at installation than later.

On tax credits: the IRS states that the Energy Efficient Home Improvement Credit, which covered skylights along with windows, applies to improvements made through 31 December 2025. Do not plan a 2026 project around it.

Choosing the replacement

• Glass over plastic for clarity, longevity and energy performance, unless the roof or budget dictates otherwise.
• Laminated inboard pane for high ceilings and over places people sit or sleep.
• Low solar gain glass on south and west roof slopes in the Central Valley. A skylight sees the high summer sun that vertical windows mostly avoid. See the best windows for cooling.
• The right mount for the pitch, and the manufacturer's flashing kit for your roofing.
• Same size where possible. Changing the size means reframing the roof opening and rebuilding the light shaft. Enlarging it usually means cutting a rafter or truss, which needs engineering.

A permit is generally required for skylight replacement in California, because the work involves the roof covering and fenestration under the Energy Code. Rules are local; see permits for window replacement. For budgeting, see our cost hub.

Sources

• 2025 Building Energy Efficiency Standards: definition of skylight (Section 100.1), Sections 150.2(b)1A and 150.2(b)1B with exceptions, Section 150.1(c)3A with exceptions
• 2025 Single-Family Residential Compliance Manual, Chapters 3 and 9
• 2025 California Residential Code, Chapter 3: Section R324.6 (skylights and sloped glazing) and Section R325.1 (natural light and ventilation)
• VELUX: Replace Your Skylight, Mounting and Flashing, No Leak Skylights, deck-mounted fixed skylight, curb-mounted fixed skylight, solar-powered skylights and FAQ
• IRS, Energy Efficient Home Improvement Credit

Working with Heritage Exteriors

Our work is windows, doors and siding, and skylight replacement overlaps with roofing. We can help you specify a skylight that meets the Energy Code and the glazing rules and coordinate it with a window project, and we will tell you plainly when the right first call is a roofer. Licensed in California, CSLB #1055919. Call (916) 546-2991.