Vapour Barrier in Attic??

I've just purchased and moved into my new home. It's about 100 years old. There is no insulation of any sort in the attic (I can't believe it's been this way for 100 years!) Of course I intend to insulate ASAP. My question is; is it necessary to apply a vapour barrier before I blow in insulation? If so, is there any spec I show know about. The winters here are very cold, with temps as low as -40, if that has any effect on the type of barrier to use. Any info or advice would be greatly appreciated!!

 

If you blow-in insulation there is no need for a vapor barrier, considering the number of layers of paint on the ceiling. What you have to be careful with are the penetrations through the ceiling. Spray foam is ideal for this application. The trick here is to identify the holes through the ceiling before you begin to seal them with foam. The easiest holes to identify will show light through when you in the attic. The rest you have to go through attic floor cavity one by one to find them. Another trick is to tack a ribbon on the rafter directly above the hole. Once all the holes are identified and the ribbons show where they are, begin to start sealing them with the foam. As you seal a hole, remove the ribbon.