Reroofing an uninsulated house
We need to reroof our A-frame which has exposed 2×6 tongue and groove ceiling with no insulation to speak of. We’re contemplating an exposed fastener metal roof (standing seam too expensive), but on top of what? I’ve been given suggestions of radiant barrier; cool roof (possibly exacerbating atmospheric warming? mold issues); metal on top of decking on top of 2×4’s on edge with fiberglass insulation; possibly others.
Priorities: 1) Reduced energy consumption 2) Comfort (which has escaped us thus far). Advice?
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What is your zip code or location? It will affect how much insulation is recommended. To keep your ceiling, reclaimed polyiso is probably the best option along with air sealing.
I suggest reading https://www.greenbuildingadvisor.com/article/how-to-build-an-insulated-cathedral-ceiling.
Simplest thing is foam, as much as you can and/or makes sense in your climate zone.
I agree with Keith. If you are only going to be working from the outside, installing rigid foam over the roof sheathing is probably going to be your best bet, though I have seen over-roofs built and the cavities filled with spray foam. Air-permeable insulation like fiberglass will be muck trickier to make work.
Without knowing where you are located, it's not possible to talk about R-values, but your unlikely to hit code minimums working just from the outside. You will want to make sure that you have enough insulation to keep the sheathing warm for condensation control. I suggest you read these two articles, which will give you a good understanding of what you are dealing with:
How to Build an Insulated Cathedral Ceiling
How to Install Rigid Foam on Top of Roof Sheathing