Mid December we noticed frost and wet areas below our insulated northeast and northwest basement wall. We have insulation on the top 4 feet of the wall per code. It has a plastic backing with a r-13 value. I also have a daylight basement with that wall framed with 3 windows and blown in insulation with a vapor barrier on the inside. The rim joists have batt insulation in them. I pulled back the insulation and had 18 feet of frost on the wall along with wet and moldy rim joists. The builder came and cleaned the mold and wanted to put in batt insulation again and hang the original insulation on the walls. We have not let them do that because we don't know why its doing it. My humidity level is 35-45% in the basement with a temp of 60-65 degrees. It was recommended we put foam board in the rim joists and hang on the walls with a good seal but not sure if this is the answer. Help would be appreciated.

Hi Leah You are about the 3 the 5th insulation basement insul problems in as many days. Id seems there is still builders and home owners going about basement insulation the wrong way
To put it bluntly there should be NO fiberglass insulation in any basement exterior walls at all. You have the classic case that I keep hearing here 3 times a week it seems. To learn even more abut it in different situations mouse over to my 21 boat and look for basement Insul/water in etc. If you need more question answered after that post back. I'm soon going to just set a format to help educate the basement problems and remedies The foberglass and poly vapor is not how any basement should be insulated Spray foam needs to be in the rim joist cavities not batt insulation
YouTube - Best way to insulate a basement 800x600 (http://www.youtube.com/watch?v=4jSuWbdJy5A&feature=related)

YouTube - Install Rigid Foam Insulation in Basement Video (http://www.youtube.com/watch?v=oNE1QQreOkA)

http://www.youtube.com/watch?v=XNe3KUmXcWk&feature=related

This explains how a basement should be insulated.

Signed 21 Boat

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