This skylight has a lot of condensation forming on the underside of the interior pane of glass. Because it's in a bathroom, the high level of humidity in the air (from showering), causes an excessive amount of condensation to form, during cold weather. The colder the  winter temperatures outside, and the higher the humidity level inside, the more condensation will form. IN Fact, the condensation was so much that it would occasionally drip down onto the drywall below and it has caused the paint to bubble.

This is an example of a skylight drainage system working properly. This Velux curb mounted glass skylight’s condensation drainage system is allowing any condensation that forms on the inside of the glass, to drain properly to the exterior. In cold weather, this continuous slow drainage of condensation, forms like an icicle.

Theres so much condensation on the inside of this skylight that you can clearly see if from outside. Eventually , all this condensation drips down into the gutters, drains down to the low end of the skylight, and is discharged to the outside.

This is something that we see quite often. The homeowner got his roofer to upgrade his vents at the same time as he was re-roofing the house. The roofer installed the large 14" turbine vent. Unfortunately, he put it on top of the old small hole (for the old passive vent that was there before), rather than cutting the hole to the size of the new vent. As you can imagine even though the new vent is much larger, it still doesn’t’t draw much air as it has to draw through a small hole. 

When installing new, more efficient venting systems, the hole in the plywood has to be cut to match the size of the new vent, for the new vent to be effective.