I'm about to get the attic spray foamed CC 2" then cellulose to R60 TOTAL. The insulation installer suggested that the vapour barrier is a waste of time?

I'm in Ottawa, Ontario, Canada, this an ICF to the rafters bungalow, any thoughts about just relying on the CC foam as a vapour barrier, I haven't talked to the building inspector yet?
 
John

Before you spray your deck, ask if your roofing (especially if you are using asphalt shingles) will still have a warranty.

I am no expert but having 2 levels of insulation sounds like a dew point and condensation problem. I'm sure someone will wade in on these possible issues.

I would think the vapor barrier would be a technical problem.

Posted By JohnyH on 26 Jan 2012 04:48 PM
I'm about to get the attic spray foamed CC 2" then cellulose to R60 TOTAL. The insulation installer suggested that the vapour barrier is a waste of time?

I'm in Ottawa, Ontario, Canada, this an ICF to the rafters bungalow, any thoughts about just relying on the CC foam as a vapour barrier, I haven't talked to the building inspector yet?
 
John

Just to clarify, you are talking of spraying the top side of the drywall ceiling and than adding the cellulose. It is a vented attic?

Yes this is a vented attic and it's on top of the ceiling drywall! John

Hi Johnny,

Please review:
http://www.buildingscience.com/documents/reports/rr-0912-spray-polyurethane-foam-need-for-vapor-retarders-in-above-grade-walls

I would agree with your contractor if it is a CC foam. However, for the cost of the polyethylene sheet, bonding to your ceiling drywall doesn't happen and any future changes to your ceiling makes it easier to remove drywall not having that bond. CC foam bonds exceptionally well if you've ever tried removing something after it has cured. Nice that you are incorporating both insulations - CC foam makes a very good airtight connection as well around any perforations through your ceiling.
Good luck.

I was in the exact same place as you this summer. I built an ICF up to the rafters with a trussed roof. I talked to the Spray foam installer about a vapour barrier. We discussed not installing, but he mentioned the inspectors in my town don't like it. He also stated that it wasn't going to cost much to install the vapour barrier.

After due diligence the vapour barrier will be installled!

John

I went through this issue last year in Toronto, the OBC does not address spray foam and not using vapor barrier. So as much as your installer is right, you still require it.

Canada is not up to date on spray foam installations like the US is, but at the same time, more spray foam is used in the US than Canada so the research dollars are spend there, unfortunately Ontario doesn't always accept US testing