Ridge Vent has Condensation on the underside after a heavy rain
 

Had new roof installed. Roofers installed ridge vents. Had a hard rain today and noticed condensation all on the underside of the ridge vent. Why?

Soffit vents blocked with insulation, no soffit vents or not enough of them.

No foam baffles and insulation blocking air flow.

Condensation is occurring because the attic air is warmer than the ridge vent being coupled to the outside air temperature. Figs. 2,4: http://www.buildingscience.com/docum...bout-diffusion

Gary

Condensation is indicative of poor airflow. A ridge vent is great, but if there isn't adequate venting at the eaves, they're all but useless. A good roofer would have checked for sufficient venting at the eaves. But, it's possible that you're fine there and that the problem is, as Joe mentioned, that the vents are blocked by insulation. Soffit baffles will solve that.

You mentioned a hard rain, which, interestingly, shouldn't have anything to do with condensation. Are you sure it's condensation and not water penetration? Did you have a hot day yesterday and a very cool night/morning?