Frost on Interior Walls

Hspirit22 asks,

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 2×6, 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 buildup 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 puzzled 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!

Our Answer

The frost is there because the surface is below the dew point and even the freezing point of water. This most likely occurs because the there is no insulation, just framing in the corner and therefore is conductive heat loss, though there could also be some issues with cold air infiltration due to wind.

The simplest thing to do would be to place an upright (floor-style) halogen-lamp fixture on the floor near the area. This will create lots of convection and radiant heat to warm the corner. There is no need for direct or close contact.

For the sliders, you can try some incandescent holiday lights hung with suction cups.