GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Insulating basement without foam

user-1137156 | Posted in Energy Efficiency and Durability on

Can a basement, that is free of bulk moisture problems, be safely and reliably be insulated from the inside without using plastic foam? My thought is: 3″ mineral wool (8#/sq ft rigid) against the concrete. Inside the mineral wool, a 2×4 stud wall with exterior face covered by ThermoPly, with seams tapped and corners caulked. The ThermoPly serves as an air and moisture barrier which prevents interior moist air reaching the cold concrete. The stud bays can optionally hold additional bats of mineral wool.

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. wjrobinson | | #1

    I have seen many dry cellars that are built from poured concrete be insulated with commercial rolls of fiberglass that comes with a layer of white poly. Have yet to find a dry cellar with moisture problems when the cellar has a hot air furnace running often as in standard days builder/developer grade leaky construction.

    The best way to find out about your build would be to build it at least a section and see results, and post results back here.

    My guess is your build would work as well as all is built.

  2. GBA Editor
    Martin Holladay | | #2

    I don't recommend your approach. The ThermoPly is a vapor barrier, and the wall assembly won't be able to dry to the interior. Any moisture that enters the stud bays from the concrete side won't be able to dry out, so it will be very easy for the studs to get moldy.

    Putting a vapor barrier on the interior side of basement studs is a recipe for mold.

  3. wjrobinson | | #3

    Martin, I read this post as saying...

    rigid rock wool

    I think you misread it to have thermoply next to drywall which would be not correct.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |