If you put a porous insulating material above a crownboard with "ventilation" holes the water vapour will escape through the holes and as soon as it hits the cold air it condenses and everything gets wet. The best idea is block off the holes with a small square of plywood and then put your insulation material on top. 25-50mm polystyrene stuck inside the roof all year round is IMHO is the way to go and has for the last 46 years for me on a poly hive. Sugar and honey stores are too expensive to waste in winter heat loss!!
Heat will permeate through the CB and condense any moist air above and lead to wet, esp. if roof vents are open to atmosphere. Forget wool and use 50mm of PIR in direct contact with the upper face of the CB.
Unless you made the roof yourself, it would have two vents fitted
Is it an Abelo poly roof? That (sensibly) has no vents.
Over the years I have used roofing felt but they do split over time - hot-cold-hot cold. I now use pondliner and it's very tough, waterproof (obviously!), easily cut and fitted, lightweight and dirt cheap. Only thing to watch is not to put your smoker on it!! However it can be easily fixed with a bit of gorilla tape. Have used it for 5 years now and haven't had a leak yet.
I used wool to insulate the hives in the teaching apiary last year and you could tell when disturbing it to add a tub of fondant that it was doing a good job as the heat hit you as you lifted it off. But, it did seem to get damp in certain conditions, I would assume when the dew point was within the fleece the condensation formed at that point and caused a damp patch.
