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 exterior above grade foundation

GrumpyIowaHomeowner | Posted in General Questions on

It all started with our porch. There is an unfinished “cold room” that has a tin roof and rusted over beam that condensates like a shower all winter from the ceiling and maybe the top of the walls.

For the sake of this question, assume we have a plan for tackling interior solutions to this issue, as well as directly adding some oomph to the exterior part of the ceiling (porch floor).

We have to futz with a bunch of the drainage and/or landscaping anyway, so we started asking ourselves what other minor “why not” adds could we add to our plan to make it a little more holistic/well rounded without much more labor/cost.

Some context: the basement is about half finished. But no matter where you are in the basement the majority of the perimeter walls are encapsulated. Presumably because they didn’t want to dig up the foundation to the footing, they added inside those fun perimeter metal braces to the foundation and a new french drain, second sump pump system. Depending on who you talk to, there was a “trickle” in the basement but they were taken to town by the basement systems company.

Since we have been here (a year including a winter) there has been no issues apart from this cold room.

Now due to what we already have going on inside, I don’t think its necessary to get overkill on insulating the exterior down to the footing.

What we did think of doing, from a cost and ease perspective, is digging 2 feet below grade, and adding some styro insulation skirt panels to add a little bit of insulation, and improve the aesthetics of the admittedly nasty looking above grade foundation exterior.

1. Waterproof the visible part, add insulation skirt panels that go 2 feet below grade up to the sill.

Is this reasonable? I don’t care if its a minor improvement, I just want to know if there is any reason I absolutely shouldn’t do this. If I’m missing something obvious.

Online, I’ve read lots of opining on waterproofing exterior above grade foundation, insulating it ranging from don’t touch it, go all the way down or nothing, why would you bother, etc. I’ll concede part of it is also aesthetic, and a desire to waterproof around the window wells, though there is no grand problem with them at the moment.

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. Expert Member
    Dana Dorsett | | #1

    There are a number of things to consider here.

    What DOE/IECC climate zone are you in?

    Is the encapsulant an insulating type? Is it somewhat vapor permeable?

    Is there a capillary break between the top of the foundation concrete and the foundation sill to prevent ground water from wicking up into the foundation sill?

  2. PAUL KUENN | | #2

    Did a shallow frost protection skirt last year using 3" used EPS about 14" down at wall with about 1" drop for drainage outboard. Just enough so perennials could grow above. Foam boards covered four feet out from foundation. This was a 130 year old stone basement. Owners said it was the first time they didn't hear loud pops and thuds all winter and noticed the walls were much warmer into December. We start seeing 0F degrees in mid to late November. Noticeable difference for sure.

  3. GBA Editor
    Martin Holladay | | #3

    It took me a while to figure out what you meant by your "cold room" -- it sounds like a basement room that extends under your porch, so that the porch floor is above the cold room. These rooms are difficult to detail.

    I hope you know that you need to retrofit (a) horizontal insulation at the level of the ceiling of the cold room (or above the existing porch floor), and most important, (b) roofing (for example, EPDM membrane). Once this roofing is properly installed and flashed at the perimeter, you can install a new porch floor above the roofing.

  4. Peter Yost | | #4

    GBA has a lot of resources on insulating either from the interior or the exterior of the foundation: just type in "foundation insulation" in the GBA search bar.

    I think your question is about the benefits of insulating just from the exterior and just the above-grade portion and then 2 feet down below grade?

    Building code issues aside: the greatest benefit from an energy perspective is insulating that portion of the foundation that sees air temperatures (the above-grade portion) and the first few feet below grade.

    In my opinion, we insulate with the same thickness of insulation from the top to the bottom of the foundation wall in new construction because:

    1. we can, easily
    2. it keeps the plane of the wall the same top to bottom

    From an energy perspective, the benefit of that same thickness does not make sense top to bottom. The delta-T does not justify it. BUT, from a thermal comfort and moisture management perspective, if you are finishing the basement, worth maintaining the insulation levels.


Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |