Insulating a Michigan roof

I have a 1200 sf ranch (california ranch, i was told) It is basically vaulted ceiling throughout, 2x8 rafters, no insulation, no attic. 1x6 for decking.

I was told that i could pull a board off every three feet. They could foam fill it 100% Then, no venting would be necessary.

After that, i would reinstall the boards i removed, throw 7/16 osb over the whole roof, then reshingle. Does this sound correct? I cant find any info so i have to go by what people tell me. Thanks so much.


That’s the hard way… you can buy polyiso insulation factory laminated to OSB or plywood (your choice) which you simply install over your existing deck. Shingles are then installed to the OSB as normal. Choose at least an R-30 in R value, which might entail using one layer of regular insulation under the nail base insulation. If you want ventilation you can purchase a vented version of this OSB/insulation board. Insulation manufacturers can provide you with installation instructions.


Looks like it would have to be at least five inches thick? R6 per inch?

They are called Hunter panels and they come in various thicknesses vented & unvented.

Just spraying in foam won’t be enough insulation and you will still get large icicles and possible ice damming.

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Ok. I did see hunter boards. And whatever I do add will be better than what i had. Thanks

Where in Mich are you?

Don and Axiom,
Though i dont live in a cold climate
I do want to learn good roofing techniques from there too.
Anything else yall want to share about why
To use vented or unvented board or a homeowner testimonial?

Vent the moisture mostly, let out the built up heat that causes ice dams.

@donl I just found this site. I have a question for you. I have read a large number of posts, and you are quite knowledgable. Please let me know how best to communicate directly with you. Thank you.