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

Best system for foundation waterproofing and insulating

MJDesigns | Posted in Energy Efficiency and Durability on

Local contractors in central OH (zone 5) are either applying a product such as Delta MS (dimpled mat) outside of the poured wall foundation for waterproofing and then applying blanket insulation on the inside of the wall in the basement … their thought being that once wet, the R-value of an exterior insulating product is severely reduced. Others are applying a damp proofing membrane such as Tremco Tuff-N-Dri to the exterior of the poured wall foundation followed by Tremco’s Warm-N-Dri 2 3/8″ R-10 foundation board (rigid fiberglass product). Which is the better method? Positioning the insulation to the exterior or the interior? If exterior, is fiberboard a better option than using EPS or XPS foam board … I read somewhere that it’s a better option as it provides for a drainage plane as compared to the rigid foam boards. Please advise. Thanks!

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. jklingel | | #1

    Besides searching here, you may want to read "Understanding Vapour Permeance and Condensation in Wall Assemblies : Volume 1: Main Report", written by the Canada Mortgage and Housing Corp and "Performing Basement Systems, Part 2....", written by the National Research Council Canada.

  2. GBA Editor
    Martin Holladay | | #2

    Either way can work fine; there is no definitive answer to this question.

    To me, the most relevant factors are:
    1. What is the R-value of the installed insulation? Of course, the higher the R-value, the better.

    2. If there is exterior insulation, is there a good plan for protecting the above-grade insulation from physical abuse and ultraviolet light?

  3. user-967937 | | #3

    I appreciate the simplicity of your answer Martin…as I plan the details of the foundation for our new home, the options and opinions can seem overwhelming at times.

    We’re also in a zone 5 and was planning a conditioned crawl space built with ICF’s., the rest of the house will be SIP’s. As I get closer to building though, I’m leaning more toward a simple stem wall design with a proven waterproofing detail on the exterior and 4” of rigid foam on the interior. The interior will be detailed for the most part as if I used the ICF’s but I’ll be able to finish the exterior of the foundation and framing on a single plane and remove the issues you mentioned above…I also figured we can save over $2k in ICF's which can be better used else ware.

    In keeping on with the original question, I’ve used liquid WRB for years on commercial buildings with great results and would like to use this on my SIP house. Is there any reason not to run the foundation waterproofing up the sheathing enough so it can be overlapped with the WRB for an air-tight (or close) seal?

    Thanks all!

  4. GBA Editor
    Martin Holladay | | #4

    Q. "Is there any reason not to run the foundation waterproofing up the sheathing enough so it can be overlapped with the WRB for an air-tight (or close) seal?"

    A. It depends on what you mean by "foundation waterproofing," as well as the width of the overlap and the details of your above-grade wall.

    Some walls are designed to dry to the exterior. Such walls shouldn't be covered with a vapor-impermeable membrane; 4 inches or so probably won't hurt, but 3 feet might.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |