The 30-second version
- Skylight condensation is a moisture-balance problem, not a skylight defect. The skylight is just the coldest surface in the room.
- Three actual causes: interior humidity too high, skylight glass too cold, or inadequate air movement across the glass.
- Three permanent fixes (in order of cost): bathroom exhaust fan upgrade, add drainage flashing kit, upgrade to warm-edge dual/triple-pane skylight.
Why skylights condensate
Warm humid air holds more moisture than cold air. When warm interior air contacts a cold surface (the skylight glass on a cool morning), the air cools rapidly and drops its moisture as liquid condensation. This is basic physics — the same reason cold beverage glasses "sweat" in warm rooms.
Whether your skylight condensates depends on three variables: interior humidity level, skylight glass surface temperature, and air movement across the glass. Fixing condensation permanently means addressing at least one of the three.
Cause 1: Interior humidity too high
Most LA homes are dry enough (35-45% relative humidity) that skylight condensation shouldn't occur even on cold mornings. Skylight condensation usually indicates elevated humidity from a specific source:
- Bathroom shower with inadequate exhaust ventilation — humidity spikes to 80%+ during showers, migrates through the house
- Kitchen without exhaust hood venting to outside — cooking humidity accumulates
- Whole-home humidifier set too high
- Un-vented gas appliance (rare in LA but occasional)
- Plumbing leak inside a wall creating chronic moisture source
Cause 2: Skylight glass too cold
Older single-pane skylights, aluminum-framed dual-pane skylights without thermal breaks, and dual-pane skylights with argon leakage over time all have colder interior glass surface temperatures than modern warm-edge dual or triple-pane products. On a 45°F LA morning, an older skylight can have an interior glass surface at 50-55°F while a modern warm-edge unit stays at 62-68°F. That 10°F difference is often the difference between condensation and no condensation.
Cause 3: Inadequate air movement across glass
Deep skylight wells (from vaulted ceilings or tall rooms) create dead-air pockets around the skylight. Warm humid room air can't circulate to the glass surface, so any moisture that does reach the glass condenses and stays. This is why condensation is often worse in taller rooms than in flat-ceiling rooms with the same skylight.
Fix 1: Upgrade bathroom and kitchen exhaust ventilation
Cheapest and often most effective. Bathroom exhaust fan should be sized to 1 CFM per square foot of bathroom (minimum) and vented directly outdoors, not into the attic. Kitchen range hood should be ducted to outside, not recirculating. Cost: $200-$800 for a bathroom fan upgrade with proper outdoor ductwork. Result: interior humidity drops from problematic 55-65% back to normal 35-45%, and skylight condensation goes away.
Fix 2: Add drainage flashing kit (temporary but effective)
For older skylights that will still be replaced in a few years, Velux and other manufacturers sell "condensation drainage flashing kits" that collect and drain condensation to a discreet drip point rather than letting it drip onto the ceiling below. This doesn't fix the underlying condensation — it just manages it. Cost: $200-$450 installed. Buys 3-8 years while you plan for eventual replacement.
Fix 3: Upgrade to warm-edge dual or triple-pane skylight
Permanent fix. Modern Velux dual-pane skylights with warm-edge spacers (LoE glass with argon fill) have interior glass surface temperatures 10-15°F warmer than older single-pane or aluminum-spaced dual-pane units. Triple-pane skylights add further improvement — mostly useful in coastal fog zones or homes with unavoidably high interior humidity. Cost: $1,800-$5,000 installed depending on size and glazing. See our Velux skylight guide for product selection.
What NOT to do
- Don't seal or caulk around the skylight from inside — this traps moisture that then goes into the wall/ceiling assembly and rots framing. The condensation is a symptom; sealing it in causes worse damage.
- Don't run a dehumidifier as the primary solution — you're addressing symptom not cause. Fix the humidity source, don't run equipment 24/7 to counteract it.
- Don't blame the skylight installation. Installation defects cause water intrusion (which shows as pooling on the ceiling below during rain), not condensation (which shows as morning droplets that dry up during the day).
Halo Build Co diagnoses skylight condensation as part of general skylight service. If you're experiencing condensation and need help identifying whether the fix is humidity-source, skylight replacement, or both, request an on-site diagnostic.
Frequently asked questions
Is skylight condensation a sign the skylight is failing?
Not directly — condensation is a moisture-balance problem, not a skylight defect. The skylight is simply the coldest surface in the room, so it's where water in humid air condenses first. Fix requires addressing interior humidity source (bathroom exhaust, kitchen hood), glass surface temperature (upgrade to warm-edge dual/triple-pane), or both.
What's the difference between condensation and a skylight leak?
Condensation appears as small droplets on the skylight glass in the morning and dries up during the day, and is worst in winter. It's uniform across the glass surface. A leak appears as pooling water on the ceiling below, occurs during or immediately after rain, and is localized. If unsure, note when it happens — condensation is weather-independent, leaks correlate with rain.
Should I seal around the skylight if it's condensating?
No — sealing traps the moisture inside the assembly, where it condenses on cool framing and can rot roof deck and rafters over time. The condensation is a symptom; sealing it in causes worse damage. Address the underlying moisture-balance problem instead (humidity source, glass temperature, or air movement).