Gary writes from Cromwell, Connecticut: "My daughter recently purchased a home in CT that was built in 1958. The attic rafters are 2x4 and the insulation is old and only 1 inch thick. I was planning to run R13 Kraft faced batts between the joists and R25 non-faced across the joists. I saw in earlier questions where you recommend not using faced batts over old insulation as it will act as a second vapor barrier. However, the old insulation is ridiculously thin and ripped in spots and I did not see any non-faced insulation for 2x4 walls/ceiling at the local home stores. Should I remove the old insulation and install all new batts or keep trying to hunt down non-faced batts?"

Answer: Because your existing insulation is so thin your plan of installing a Kraft insulation over top is fine. Rule of thumb is that the vapor retarder needs to be in the warmer third of the insulation. Since you are installing over 11 inches over top the Kraft vapor retarder will be well within that third.