Frost on Interior Walls

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2 expert, -1 community

We built a ranch style home in 2012.  When it is extremely cold (below zero) and the wind blows we find areas of frost on the the interior walls @ ceiling level.  The exterior walls are 2x6, with blown in fiberglass insulation.  The attic is insulated to 48 R with blown in fiberglass.  The attic is ventilated with soffit vents and ridge cap venting.  Interior humidity runs 34-38%. We have Anderson 100 windows and do get moisture and ice built up on them as well, I get the ice on the windows but struggle with frost on the interior walls.  The general contractor and insulating contractor are puzzeled as well, but are still working with us.   Looking for ideas on identifying and correcting the problem.  We have lived in SD all our lives(55 years) in numerous houses both new and older and have never seen any frost on interior walls. Thanks for your help