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Question
I was hoping to save a bit of cash as were running out fast with our renovation. I was wondering if we could use a combination of fiberglass and sprayfoam. I was hoping to put R-12 fiberglass and then cover it with closed cell sprayfoam to finish off filling the 2X6 walls. I live in Northern Ontario and by code need a R-22. If this is not possible, can I get the walls sprayfoamed first with closed cell and then put the fiberglass? If I was to do this, would I need a vapour barrier? I love the idea of sprayfoam to stop air movement, but would really like to get the benifit of a moisture barrier as well. What about the ceilings? Is there anyway to be able to take advantage of the benifits in the attic on the cheap. Thanks alot. Ray
 
Answer
SprayFoam.com

Ray,

We call the combination of spay foam and air-permeable insulation, hybrid. Hybrid installations are possible by one of two methods:

1. Install a 0.5-1” flash spray of foam then fill the remaining cavity with your air-impermeable insulation. You will definitely need a vapor retarder on the interior side of this assembly. This is not the best option, because if the vapor retarder fails, there is a good chance that condensation could occur on the cold spray foam layer.

2. Install enough spray foam so that by adding the layer of air-permeable insulation, you will not have condensation at that juncture. In your area you’d need around an R-10 of closed-cell spray foam with an R-12 batt of air-impermeable foam.

For the roof deck, you may need around an R-30 of the closed-cell SPF and an R-19 amount of air-permeable insulation to finish the cavity.

It is possible, but you need to be careful. Also, these recommendations are assuming you are in a climate zone 7 per ICC-IECC building codes. Please consult with your contractor and/or the foam manufacturer that you choose to ensure you will not have any condensation issues.

Feel free to click on the "Contact the FAQ Administrator" to ask me a follow-up question.

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