GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter 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 an unheated, concrete walk out foundation

braydee | Posted in Energy Efficiency and Durability on

Building an unheated boat house -architect design lower level to be poured concrete and slab built into a hill, with 4th side open to a lake. Wood framed shed like structure above. I’m concerned about condensation in the summer so would like to insulate under slab and foundation walls, but what will happen to slab and foundation when exposed to ambient temps of NH’s winter? Which is the bigger risk? Or insulate and Construct super insulated/tight doors?
I would appreciate any thoughts.

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. GBA Editor
    Martin Holladay | | #1

    You will never totally eliminate condensation in an unheated building, but insulating under the slab and on the exterior side of the foundation walls can't hurt. The insulation will reduce the amount of condensation.

    In the spring, when a period of cold weather is followed by warm, humid weather, you will get condensation. That's just physics.

    Don't worry about the integrity of your building, however. Unheated sheds and barns on good foundations can last for hundreds of years.

  2. braydee | | #2

    Thank you Martin...and of course I've seen many hundred year+ old foundations in good shape. But then, I've never seen a hundred year old foam insulated foundation with on grade level insulated slab. I'm guessing neither has anyone :)

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |