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Will a non-waterproofed foundation freeze in the winter if insulated on the interior?

David Cook | Posted in General Questions on

This question has arisen on many reno projects where the homeowners do not want to pay to have the old foundation waterproofed. Of course, we want to insulate the basement but there have been some voices who have stated that insulating would cause the “wet” foundation to freeze in the winter and thaw in the summer and thus, over time, deteriorate. Is this a valid concern? Or is there little to no risk of the foundation itself freezing? Thanks.

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Replies

  1. Riversong | | #1

    Unless the foundation is liquid, it's not going to freeze.

    But I suppose you're asking if freeze-thaw cycles can damage a foundation over time, and that depends on the type and condition of the foundation, the seasonal saturation level of the site soil, the proximity of the water table and the capillarity of the soil, the type of backfill used, the surface grading and presence or absence of gutters, downspouts and leaders, whether the foundation was damp-proofed...

    Masonry and stone foundations in wet soils are far more vulnerable than poured, reinforced concrete, for example.

    So, what's your question?

  2. GBA Editor
    Martin Holladay | | #2

    David,
    Concrete foundations freeze all the time. Many unheated barns have poured concrete basements. Don't worry.

  3. Riversong | | #3

    Concrete doesn't freeze, it cures ;-)

  4. John Klingel | | #4

    Isn't insulating on the OUTside generally a good idea? I don't see how the foundation could be hurt if kept warmer. Why not dig it out, water proof, insulate(flash, etc), and bury it again? j

  5. David Cook | | #5

    Thanks for all your replies. We seem to have covered concrete but all of the old home we renovate are typically around 80 years old. To my memory not one foundation has been concrete. So for stone/brick/masonry foundations: if a customer refuses to have the foundation waterproofed is it best to leave the foundation uninsulated? Or is there another solution?

  6. Roy Harmon | | #6

    There are many variables to be considered before deciding. Each project could have a different approach depending on the existing conditions. If there are no interior moisture problems to begin with, you might consider a compromise by damp proofing and insulating down to the frost line. Detailing at the bottom of the insulation would require a well executed system to move or direct any potential water away from the foundation. Cost would be a lot less than doing the full foundation unless the frost line is 6' deep. I would then insulate the inside without worry. It would be very important to first understand the reason for refusing damp proofing and or insulating from the outside. Sometimes messing with a masonry foundation~ stone, brick etc. on the outside, brings about problems that otherwise may never occur. The proper bonding of any material used on the outside of masonry that has been "in ground" is a critical factor to be considered.

  7. Riversong | | #7

    David,

    There won't be a freezing problem unless the soil around the foundation can get saturated. Get rid of the water sources and you've eliminated the problem. Gutters with leaders at least 10' away from foundation, grading of at least 5% for at least 10', swales, French drains to interrupt surface and subsurface flows, etc...

    If the foundation is allowing water entry, then there is an existing problem that must be corrected before insulating the basement. If it's bone dry on the inside, there's not likely to be a water problem on the outside.

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