Where is the correct vapor barrier location in Chicago?

Joel Peerson
Updated: Feb. 3, 2021

I live in a 1970's era raised ranch in the metro Chicago area.  The foundation walls raise 4.5 feet above grade.  The floor joists on top of the wall extend out 30 inches from the foundation wall.  There is an overhang, common in a lot of raised ranches.  I want to insulate this "overhang" area.  The floor joist is 7".  So 2 batts will fit in the area.  What to do about a vapor barrier??  I can place a poly sheet at the top closest to the floor of the upper level or at the bottom on the side closest to the outdoors.  Or I can maybe put on some vapor retardant paint on some of the surfaces.  I hope my question and explanation is clear and there is an opportunity to respond.  I look forward to your advice. 

Thank you, Joel Peterson    

Responses (2)

Joel Peerson 3 years ago

Thank you for your reply.  Sorry I was not more clear that the overhang is enclosed.  The home's exterior siding goes down to the bottom of the floor joist and the bottom of the floor joist is covered with 2 layers of 3/8 plywood, the layers separated by about 1 inch of space.  The bottom plywood coverings go to the foundation wall.  The interior wood surfaces of the space are untreated.  The overhang space is accessible only from the basement.  Does this information modify your advice?

Thank you very much, Joel Peterson