Best economical way to seal a tongue & groove ceiling with rigid foam

Green Building Q&A: Best economical way to seal a tongue & groove ceiling with rigid foam

My son's house has the notoriously leaky tongue & groove ceiling with fiberglass batt insulation. Our plan is to pull up the fiberglass batts and foam seal in rigid foam between the joists. Because finances are an issue, we will probably do it in steps and have to re-use the fiberglass over top. Then when it is complete, we will add blown in cellulose on top. What would be the minimum thickness and best type of rigid foam to use for this? When re-using the fiberglass, do we leave the paper facing on, or should it be removed?

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