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Below grade insulation/waterproofing

mfredericks | Posted in Green Building Techniques on

I’m hoping for some advice on my proposed waterproofing plan. I have a 60 year old house that has a small leak in the basement and I expect to see more leaks as that the house is built into a hill and there seems to be a lot of water in the soil against the bare concrete foundation.

We intend on creating living space in the basement and would like to waterproof and insulate the exterior of the foundation. We have incentives from our provincial efficiency group for adding R10, so I’m planning on 2 inches of XPS to meet the requirements for this rebate. However we have a lot of ants around our house so I’m concerned about them eating into this XPS. So to get good waterproofing/insulation, and insect protection, my plan is to:

-excavate around the foundation and clean the surface (repair any damaged areas)
-roll on asphalt damp proofing
-R10 XPS down to the footing
-Wrap the XPS with Blue Skin peel and stick membrane, (wrap over the footings)
-install a new footing drain
-backfill with clear gravel

This has added up to an expensive build out and I’m not sure how well the Blue Skin will adhere to the XPS or if there’s another product that would be more appropriate to protect the insulation from insects while also adding another water barrier.

Any thoughts or ideas would be appreciated!

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  1. Expert Member
    ARMANDO COBO | | #1

    Why don't you excavate, clean, fix and waterproof the outside of the basement walls, and then insulate the interior of the basement.
    Marc Rosembaum just wrote 2 blogs about it:, and
    Here is a blog from Martin Holladay:
    You also need to have positive drainage outside the house, guttering system away fom the foundation and possibly exterior drainage to a pump.

  2. GBA Editor
    Martin Holladay | | #2

    A layer of plastic dimple mat on the exterior is always a good idea -- especially if you are going to the expense of excavating down to the footing...

  3. mfredericks | | #3

    Thanks guys,

    Martin - do you think the dimple board would be a good additional step to protect the Blue Skin membrane during backfill, or could this mat replace the membrane and save me some money? I'm interested in having a really waterproof and insect proof barrier which is what led me to the peel and stick membrane placed over the XPS, even though it's a bit expensive. I'm just unsure of how well it would hold up.

    Armando - we've already insulated the interior of the basement using a very similar approach shown by Marc. We did this in the winter when we couldn't do much exterior work and completed the whole basement with the exception of the area around the small existing leak. We're now ready to excavate outside to solve this water problem and figure if we have the foundation exposed we may as well add exterior insulation, especially with the available rebates.

  4. wjrobinson | | #4

    Mark, no guarantees when using exterior insulation. Local exterminators and longtime builders there would be worth talking to. And there may be no payback. Another thread mentions resistant products.

    I am not an overkill advocate. Keep it simple. But have backup plans when flying in a space shuttle.

    Only you and onsite contractors know how bad your water problem is. Near me we have specialists and their guarantees.

    Myself, I would skip the insulation, and just tar and poly for low cost or move up to membrane if the budget was there along with scarey water veins and puddles. And proper drain piping, gravel, etc.

  5. GBA Editor
    Martin Holladay | | #5

    You might want to consult with local waterproofing contractors on this issue.

    It's better to follow an approved foundation waterproofing system, and to follow a manufacturer's instructions, than it is to devise your own details.

    Here are links to two dimple mat systems:

    Delta MS

    System Platon

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