William writes from Ossining, New York: "I have a home built around 1955. My attic has some fiberglass insulation and blue Styrofoam boards covering the fiberglass on the attic floor. I don't plan on using this space. Can I roll r-30 unfaced insulation over the top of these boards or do I need to pull the boards out and roll the insulation on top of the old insulation? Should I use raft-r-mates if this is the case, and will 2" soffit vent circles provide enough airflow?"

I recommend that the polystyrene foam be removed since it should not be left exposed. That is a code violation.

Roll the new insulation directly over the existing fiberglass insulation.

Use RAFT-R-MATE® attic rafter vents only at the eaves where the insulation meets the roof deck.

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.