You noticed it after the last rain — a brown ring on the ceiling drywall, right below the skylight. It might be small. It might have been there longer than you think. Either way, it won’t fix itself, and the longer it sits, the more it costs.
The 4 most common skylight leak causes
Skylights leak for a handful of reasons, and almost none of them are the skylight’s fault. The glass or acrylic dome is usually fine. The problem is almost always at the connection between the skylight frame and your roof.
1. Failed step flashing or saddle flashing
Flashing is the thin metal that seals where the skylight curb meets the roof surface. Over time, San Diego’s thermal swings — hot, dry summers followed by winter rain — cause metal to expand and contract. That movement works sealant loose and can lift flashing edges away from the curb.
2. Dried-out butyl or silicone sealant
Most skylight installations use a butyl tape or silicone bead along the frame. UV exposure degrades both. A skylight installed in 2010 has sealant that’s 15+ years old. It’s not a question of if it fails — it’s when.
3. Condensation mistaken for a leak
This one trips up a lot of homeowners. If the stain appears during cold nights rather than rain events, you may be looking at condensation dripping off the glass interior. It’s still a problem worth fixing, but the repair is different — usually improved ventilation or a thermal-break upgrade, not a roofing fix.
4. Cracked or crazed dome
Older acrylic skylights crack from UV exposure and thermal stress. A hairline crack in the dome lets water in directly. If your skylight is original to a home built before 2005, check the dome itself for yellowing or crazing — that acrylic has likely reached end of life.
How to tell if it’s the flashing or the seal
This distinction matters because the repairs are different in scope and cost.
Signs it’s the flashing:
- Water appears during moderate rain, not just heavy downpours
- You can see daylight or daylight gaps at the skylight corners from the attic
- Staining is concentrated on one side of the ceiling, not spread evenly
- A roofer finds lifted or missing flashing on inspection
Signs it’s the seal:
- Water seeps in during wind-driven rain specifically
- The stain follows the full perimeter of the skylight opening
- Sealant around the frame is visibly cracked, shrunk, or missing in spots
A good first check: get in the attic with a flashlight during or right after rain. Look at the skylight curb from below. Fresh moisture tracking down one side of the curb almost always points to a flashing failure at that corner. Moisture coming in at the frame edge is usually sealant.
If you’re unsure, a roof inspection by a licensed contractor gives you a documented answer before you spend money on the wrong repair. It’s also worth ruling out other nearby penetrations — pipe boots are a surprisingly common culprit that gets blamed on skylights. Our post on pipe boot leaks in San Diego covers what to look for there.
Repair vs. replace: the 10-year rule
Here’s a straightforward way to think about it: if your skylight is under 10 years old, repair almost always makes sense. If it’s over 20 years old, replacement is usually the smarter spend. The 10-20 year window is where you have to think more carefully.
Repair makes sense when:
- The frame and dome are structurally sound
- The failure is isolated to flashing or sealant
- The skylight is a quality brand (Velux, Fakro, or similar) with available parts
- The surrounding roof is in good condition
Replacement makes sense when:
- The acrylic dome is yellowed, crazed, or cracked
- The frame has visible rot or corrosion
- You’ve had the same skylight repaired twice in five years
- Your roof is due for replacement anyway — skylights should be replaced with the roof whenever possible
Replacing a skylight during a full skylight installation project is significantly cheaper than doing it as a standalone job later. Roofers are already working the same area, scaffolding is set, and the tile or shingle work is already open.
One more factor: if your roof is tile, adding or replacing a skylight on a tile field takes more labor than on a shingle roof. The surrounding tiles have to come off cleanly, the flashing has to be custom-fit to the tile profile, and everything goes back in the correct order. It’s not a quick job, but a good crew does it right the first time.
What a skylight replacement costs in San Diego
Prices vary based on skylight size, type, and roof material. Here’s what you can realistically expect in San Diego County as of 2026:
Flashing and sealant repair only: $350–$700 for most single skylights. More on tile roofs where surrounding tiles need to come off and go back.
Fixed skylight replacement (like-for-like): $900–$1,800 installed, depending on size and brand. Velux FCM fixed units in the 22×46 range typically land around $1,200–$1,500 installed on a shingle roof.
Venting skylight replacement: $1,400–$2,800 installed. The venting mechanism adds material cost, and solar-powered venting units (no electrical required) are increasingly popular in San Diego given the sun exposure.
Curb-mount vs. deck-mount: Curb-mount skylights are easier to flash correctly and tend to hold up better long-term. Deck-mount units sit lower-profile but require more precise installation to avoid recurring leaks.
Permits: San Diego County requires a permit for skylight replacement in most cases. Check requirements at the City of San Diego Development Services or San Diego County PDS depending on your jurisdiction. Any contractor who tells you a skylight replacement doesn’t need a permit is worth questioning — verify their license at the CSLB license check tool before signing anything.
When ceiling stains mean the leak’s been going for months
A fresh leak leaves a wet ring. An old leak leaves something worse.
If the drywall around your skylight is soft, bowed, or crumbling, water has been infiltrating longer than one rain event. That means the damage has likely moved beyond surface staining into the roof deck, the rafters, or the insulation above the ceiling.
What to look for:
- Drywall that feels spongy or gives when pressed
- Mold or mildew smell in the room below
- Paint bubbling or peeling in a radius around the skylight frame
- Dark staining on the ceiling that extends beyond the immediate frame area
When you see these signs, the repair scope expands. It’s not just a flashing job anymore — it potentially involves replacing sections of sheathing, treating for mold, and repairing the ceiling from below. Getting that assessed early limits how far the damage spreads.
If water is actively coming in right now, our emergency roof repair team can tarp and assess same day. For a full picture of what’s happening at your roof — not just the skylight but all penetrations, flashing, and field condition — our roof inspection checklist post walks through what a proper inspection covers.
When to call us
If your skylight is showing stains, dripping during rain, or you can see daylight gaps in the attic, it’s time to get eyes on it from a licensed roofer — not a handyman with a caulking gun. Sealant-only patches on failed flashing buy you one rainy season at best. Call us at (858) 925-5546 for a same-day estimate.