Greg writes from Portland, Oregon: "I have a 40's house with a finished attic that has 2x4 rafters. Given my "zone" I'm recommended to have R-38 in the attic space, which I can get above the collar beam and then enough at the knee wall but not at the area in between (whatever that's called). I've seen suggestions that say I should "fir" out the 2x4's to allow for more space, however an additional 8 inches out would close in that space considerably! With so little space to work with should I consider not putting in rafter vents and just fill with insulation and then install gable venting??"

Answer: Lack of proper ventilation may affect your roofing manufacturer's warranty. A minimum one-inch airspace is typically required when insulating under a roof deck. Unfortunately, you do not have an option for achieving an R 38 insulating value in 2 x 4 spacing. We typically suggest furring as you have described.