Vapor barrier or not

[vtcnc]

Airflow through the soffit vents, through up-and-between each rafter section and up through to the ridge vent.

Ice shield is obviously on the outside between roof sheathing and shingles.

I got a ridiculous deal on 2-1/2” foam board. Cut each section to rafter bay width and stuffed them between till they were flush. Probably about an 1” gap behind the insulation and the roof sheathing. Drywalled over the top. My shop is ridiculously airtight and I use the upstairs as heated dry storage. Room temperature in the winter and almost never turn on the AC in the summer.


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[MyLilMule]

As long as you have unrestricted airflow from soffit to ridge vent you should be good with out an interior vapor barrier.

I’m in NW Vermont, I did put ice shield on the roof sheathing as an added layer of protection. But inner barrier for insulation. I used foam board and left the gap behind it.


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My entire roof (shop, house, garage) has ice and water shield under the shingles. I'll never do another roof without that. It's cheap and is multitudes better than just tar paper.