Conflicting information on vapour barrier.

Trevor Karbashewski
Updated: April 25, 2023

Hello! I purchased a 50s era home last year and am looking at upgrading the attic insulation. Located in Calgary.

Right now there is cellulose almost up to the joists, and under that is a paper backed (both sides) layer of old fiberglass it looks like (it's black). So it could use a lot more. I had one company come look at it and they wanted to vacuum it all out, spray foam for a vapour barrier, and then loose fill. It was too much money for me, so I've decided to tackle it myself.

I have some recessed lights to seal and cover, bathroom fan to vent, attic voids above closets to seal, and baffles/insulation stops to install for ventilation. All that I can handle.

I had another contractor come out to take a look for quoting me on doing the loose fill once all my prep is done. He said to do all the prep I was planning, but not to worry about a vapour barrier; just loose fill right on top of what's there.

I found your website and I see some conflicting information.

This article ( stresses the importance of a vapour barrier: "But, if you have no air barrier at all, you really do need one. This requires lifting insulation, laying down a polyethylene vapour barrier over the whole surface (it can go up and down over joists) then reinstalling the insulation.".

But in this article (, specifically in the comments section, ecoHome suggests that a vapour barrier is not necessary.

Right now the attic has no serious problems. No ice or moisture build up. It's just poorly insulated and I want to get it to R50. I really don't want to introduce more problems by not doing this correctly.

Should I lay down a poly vapour barrier? It would be quite difficult with my truss design.



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