Question: How should I insulate walls and under a flat roof?
Jay writes from Mesa, Arizona: "I have 2X6 exterior walls with a 2X10 flat roof on my addition. What would be the appropriate insulation to install? I want the best insulation value for the space."
Answer: The best you can do in this situation is to install R-21 fiberglass insulation in the 2 x 6 walls and R-38C in the 2 X 10 joist.
If you have an open attic space above the 2 x 10 joist, I recommend using blown in insulation. You can get more R-value and it will be more affordable.
