Peter writes from Saint Paul, Minnesota: "I was planning to insulate a 2x4 cathedral ceiling with R-13 batts in the cavities and 1" Foamular attached to the interior side of the rafters. Does it matter if the batts are faced or not? Is it necessary to tape the seams of the Foamular?"

Answer: In your area you should use Kraft-faced insulation. Taping the seams is recommended but not required. I am not sure exactly what you have in mind for your total assembly but remember that building codes generally require covering foam insulation with a product having a 15 minute thermal barrier, such as gypsum drywall, for fire safety.