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I am rebuilding a house and the sill plate is below grade

Michael Kasales | Posted in Green Building Techniques on

I am putting new ZIP sheathing over the whole house but 10 inches is below grade. I was thinking of putting Durock below grade for the 10 inches but some say pressure treated plywood might be better? Either product will be treated with a waterproof coating and then 3 inches of rigid foam then a stone exterior which is best or can I use something else? The foundation is block they just build it below grade …


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  1. GBA Editor
    Martin Holladay | | #1

    You've got a major problem on your hands.

    The correct solution is to lower the grade by at least 18 inches.

    If circumstances don't allow you to lower the grade, you should hire a house-moving company to jack up the house so that the foundation can be raised 18 inches.

  2. Michael Kasales | | #2

    Thanks but that's not going to be an option of house raising. The house is 24 years old and only one spot has rot from improper grade sloping to the house. I have 2 inches of insulated R 10 drain board which should carry any water load to the base of the basement wall. I know they build homes of pressure treated wood foundations..not good but I still need an option ?

  3. GBA Editor
    Martin Holladay | | #3

    Can you lower the grade?

  4. Michael Kasales | | #4

    No I can not lower the grade... They make a PVC panel as well very expensive but not sure how well that might work ?

  5. GBA Editor
    Martin Holladay | | #5

    It's one thing to engineer an All-Wood Foundation on a new house, using pressure treated lumber, pressure-treated plywood, stainless-steel fasteners, many truckloads of below-grade crushed stone, and a well-engineered underground drainage system.

    Trying to solve a problem with a 24-year-old house that has been mistakenly backfilled 10 inches above the sill is an entirely different matter.

    I think you are making a mistake. I advise you to lower the grade or jack up the house.

  6. Michael Kasales | | #6

    thanks for your help ....

  7. David Kominek | | #7

    Why not just build a retaining wall to stop the soil just short of the wall, creating a space between the wall and the soil. That way you do not have to worry about the potential of any wood-to-ground contact.

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