Karl writes from Smithfield, North Carolina: "Some of the insulation in my un-heated crawl space became wet at one time and is falling down or looks like stalactites in a cave. Steps were taken to air the space out and it's been pretty dry now for a couple of years. My question is: Can I put new insulation over top of the old stuff or should I remove the original material and replace it all? I plan on using R19 Faced to do the job either way. I can't tell what type of insulation is now in there except to say that it's yellow and has a paper backing."

Answer: If the insulation is dry and was not damaged by contaminated water, it can be left in place. In this case we recommend adding only UNFACED insulation. Adding insulation with a vapor retarder introduces a second vapor retarder to the system and may cause moisture issues. If you choose to remove the existing, however, you should replace it with insulation that has a vapor retarder. We recommend having a total of either R-19 or R-25.