Do roof windows (velux) have a drainage system so you can keep them a little open at night?
Don't think do, most skylights do not open, those that do need to be closed if the weather becomes a problem.
They don't have a drainage system, but they do have a way for water that condenses on the glass to collect and evaporate, so that it won't run down your trim and stain your woodwork or ceiling. If you don't have an electric closer with the rain sensor, you may want to be careful just how much you leave them open. Water can splash in off the roof. So, no worries on condensation but be careful of the hard, driving rain splashing off the roof and in your house thru the open skylight.
