Is an emulsioned ceiling a vapour barrier?

I am lining my 1930's rafters to stop all the **ap flying in, therefore ventilation will be greatly reduced, so I need to make sure there's no moisture getting in there. My bathroom underneath has ELV downlights in, so I'm gonna need to seal them up somehow taking into account the heat build up (any ideas?). During the winter the outside wall streams with condensation (9"solid wall) after a bath/shower, do you think that moisture can also get through the emulsion and permeate it's way into my loft?

You need to fit an extractor fan or at the very least keep the bathhroom window open
Steamy air will condense on cold surfaces so why take the risk of it migrating to your loft. (I wouldn't of thought it would get that far)

MM

As suggested, an extractor fan is the best solution. Remove the moisture laden air before it has time to cause problems rather than having to solve the problems it causes.

You could also take a look at these:
Downlight Fire, Vapour & Thermal Seal Cap

Thanks Davy, gonna get me those hoods, on the subject of extractors, I fitted one in my last house..........hopeless, the thing wheezed away n never got the job done n that was fitted direct into the wall