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I have a 1989 house with a cathedral ceiling built 2x10 rafters 24" oc. I am about to redo the roof, which would give me a chance to pull up the decking and improve the insulation.

I am guessing the insulation is fiberglass batt with no ventilation baffles. What I want to do it put in the plastic baffles to ensure good air flow from the soffit to the ridge vent.

One concern is since these baffles are plastic and not breathable, will I be trapping moisture in the insulation below them?

Also, should I bother with baffles where there are skylights fit between two joists with no way for air to pass them?

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To answer the question, the baffles allow air all around them, with the exception of spraying foam insulation on one side of them, so it does not matter if they are breathable or not.

In my opinion, if the insulation was done properly, you should have 8" of insulation, perhaps only 6", stopping at the wall, and not going into the soffit. The air space over the top of the insulation to allow for air flow, you should not need any baffles. Check out the possibility of adding rigid foam over the sheathing to adding more R value to your existing. If you use 1 1/2' foam 2" edge flashing will still cover without looking too much out of place. This type of install may only help with the summer heat, but not the cold of winter.

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