Fog trapped between skylight panes is a failed insulated-glass seal. The haze sits inside the unit. Wiping the room side does nothing. Wiping the roof side does nothing. It is not the same problem as condensation on the glass you can reach.
Austin humidity makes the mix-up common. A Hyde Park bath can dew the room-side glass on a cool morning and look milky from the hallway. That film wipes off or fades as the room dries. Between-pane fog does not.
The wipe test
Stand under the unit. If you can smear the haze with a cloth, you are on the room surface. That is condensation or a leak, or ordinary household film. If the haze sits in a layer you cannot touch, you are looking through two panes at moisture that entered when the edge seal failed.
Between-pane fog often starts at a corner and creeps. It can look like a cloud that never moves with the weather. It can show mineral trails where water dried between the lites. None of that is a roof leak by itself. The unit is still a closed sandwich. The view and the light are what fail first.
A leak is water in the well, on the ceiling, or in the insulation, timed with rain. Run the drip-location test on the leak diagnostic page if you have both fog and a stain. They can coexist after hail or after years of a slow curb leak.
Why Austin seals fail
Insulated glass is two lites, a spacer, and a seal. Heat, UV, and pressure cycling work the edge. Central Texas does all three. Summer attic air is harsh. A south-facing unit over a Round Rock living room takes more sun than a north unit on the same roof.
Hail is a second path. The September 24, 2023 storm was the costliest Austin-area hailstorm on record, with about $600 million in estimated losses across Travis and Williamson counties and hail up to about 4 inches in Round Rock. An impact can break the seal without shattering the pane. The glass looks whole. The haze shows up later.
Age is a factor without a published year count on this page. A specific average service life for skylight insulated glass could not be confirmed. Read the unit label. Ask the independent installer what the maker still supports. How long skylights last in Austin stays on that honest gap.
What fog does not tell you
It does not, by itself, mean the curb is rotten. It does not mean the flashing is open. It does not mean you need a full unit until someone checks the frame.
It does mean the insulated-glass unit has failed as an insulated unit. You will not restore the original clarity with a cleaner. Desiccant tricks and drill-and-fill kits are not a recommendation here. No verified local result for those methods could be confirmed.
If the frame is sound, when glass needs replacing is the next read. If the curb is soft, skip glass-only hope and go to repair or replace.
City of Austin Climate Zone 2 maxima for skylights are U-factor 0.60 and SHGC 0.28. A new insulated unit should be checked against those tables. Confirm the current numbers with the city and the product sheet.
What the pro should confirm
That the haze is between panes, not on a surface. That the curb can take a new insulated unit. That flashing can stay or must come off with the glass. That the replacement ratings match the energy tables for your address, whether that address is in Austin city limits, an ETJ, or Williamson or Hays County.
A dollar figure for glass-only work could not be confirmed here. Access, coatings, and size change the quote.
Bright Sky ATX is a referral service. The pros we send inspect the unit. We do not replace glass ourselves.
When to call us
Call when the skylight looks permanently cloudy and a cloth does not touch the haze. That is skylight glass replacement for an experienced, insured independent pro. Call (737) 477-8898.