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

Waterproofing Foundation Wall

Singsing | Posted in General Questions on

This question concerns a 60 year old winterized cabin in Quebec (climate zone 6). It sits on a concrete block crawlspace wall that is insulated with EPS on the inside. There’s a poured concrete footer below the wall. The foundation is only 4 blocks high (so 32″). The foundation is not as deep as it should be, given the 4 ft frost line. But the footings appear to be intact and level.

I’ve just excavated and replaced a 25 section of the block wall (including a corner) which was cracking horizontally (half way up the wall) and starting to cave in. The soil is a mixture of sand and clay: it it seems probable that hydrostatic water pressure was to blame for the damage.

The new block wall now has rebar and grout every 2 feet, so it should be sturdier. Gutters keep rainwater from the roof at bay, but the grade on that side of the cabin slopes uphill, and presumably receives a lot of seepage from the hillside above.

My questions are:

1. given the crawlspace has a dirt floor (and will be encapsulated with polythene sheeting) is it necessary to waterproof or use dimple mat etc to prevent water ingress? Would it help strengthen the wall? Or is waterproofing only recommended for finished basements?

2. The grading makes it virtually impossible to daylight a french drain. Is it still worth laying drain tile anyway, even though it doesn’t ‘go’ anywhere? (perhaps terminate in a dry well?)

3. What should I use to backfill? I had planned to backfill with 3/4″ clean gravel, lay landscaping fabric and then top the gravel with 6″ of clay. Would it be worth laying rigid foam horizontally above the gravel to keep the CMU wall warmer?

Many thanks in advance for your 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. user-2310254 | | #1

    Hi Leo,

    I'll give your post a bump.

  2. Lindaloowho | | #2

    I thought you might find this interesting.

  3. GBA Editor
    Kiley Jacques | | #3

    Hi Leo,

    Here is a recent post about damp- and waterproofing foundation walls by Scott Gibson. He discusses a number of products and “good-better-best” approaches to situations like yours. There is also some talk about drainage, and additional resources that may help inform your plan.

  4. Singsing | | #4

    Great, many thanks for the links.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |