Kathy writes from Azusa, California: "I live in a uninsulated house with a metal roof. The attic area is also a non-vented space. What is the best R-value to use with fiberglass batts? I'm thinking R-38 - my dad is leaning toward R-30."

Answer: Are you putting me in the middle of a family disagreement? It seems as though I am sure to upset one of you and that makes me uneasy.

I could duck the question, of course, by sending you to your local building department. They should have data on the best R-values to use. And thermal insulation levels must meet or exceed local requirements, although your home doesn't seem to at the present time.

Another option for me without taking sides is to recommend that you fill the cavity of the attic joists. For example, if you have 2x10 joists install R-30; if you have 2x12 joists install R-38.

I can also avoid picking either R-value by telling you that the U.S. Department of Energy recommends R-49 for most areas of the United States.

If you expect to keep the home for a long time, the insulation with a higher R value should eventually pay for itself by saving energy, which will also reduce your carbon footprint.

It is really your call - but I'm on your side. (Don't tell Dad and get me in trouble.)

Finally, adding ventilation will also help your insulation work more effectively, especially in the summer when air movement will allow heat to escape. You will need to do some math to calculate your ventilation requirement. The minimum ratio is 1/300. That means you need one square foot of ventilation for every 300 square feet of attic space. We recommend a ratio of 1/150.