Velux has a 20 year warranty on their IGU system against fogging. I would expect it to last a lot longer than 20 years.

There is no better skylight available than Velux.

They are incredibly well engineered these days.

Have you had the old bubble acrylic skylights or glass? The acrylic ones are notorious for fogging (it’s actually the plastic crazing). I’ve used the velux a dozen times with no issues including my last two personal homes.

We installed a Velux operable skylight with double pane low-e glass in 1986. Still AOK.

I installed a Velux skylight (fixed) a couple years ago to replace an old-style acrylic dome. It's an enormous improvement. Not only much brighter, but the LowE coating on the Velux that was not on my acrylic bubble means the sunlight directly underneath the skylight is not hot at all. It was quite hot under the acrylic dome in summer. So the light streams in much brighter, yet is not as hot. And the double-pane glass also means the cold air in winter does not seep in the way it did with the acrylic dome. I've never seen condensation on it. Would recommend the Velux highly.

We had our skylights replaced with Velux in 2013 when our roof was replaced. The one in the kitchen is operational, the one in the master bath is stationary. We wish we had done both operational. We have had no issues with fogging, steaming, leaking or anything else.

Have 2 Velux Solar/Rain Sensor Skylights. One is 7 years old and the other replaced another brand that was 25 years old 2 years ago Highly recommend

We had a Velux skylight put in new 20 years ago when we got a new roof installed. No issues whatsoever. Tornado hit our house 8 years ago and did quite a bit damage to roof right near where Velux skylight was - had to get another new roof but same Velux skylight. Again, no issues whatsoever! Wouldn't install anything but a Velux!

Avoid Velux if you can. They do not actually offer any meaningful support or genuine troubleshooting long term, even if you want to pay for it. The shades break, and support has no sense of how to actually help customers.

We have had two sets of Velux skylights over a 35 year period. Never had an issue with leaking or fogging.