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Community and Q&A

Need for waterproofing?

Brian Adams | Posted in General Questions on

I’m in the process of sealing our crawlspace now during building. Our land gently slopes and our crawlspace goes from 2’ish feet to about 6 feet. Typically, only the bottom block at any point might be under grade. The garage, slab on grade, is attached to the uphill side. 

Do you think we still have a necessity to lay drains and waterproof the exterior of the block?

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Replies

  1. Expert Member
    Malcolm Taylor | | #1

    Brian,
    Yes you need both. You can get away with omitting the perimeter drains on the low side of your foundation, but without one on the top and sides you will end up with water making its way under your footings and coming up somewhere on your sloped crawlspace floor.
    Having your footings that high will make installing the drainage a bit tricky. I usually aim for at least 18" between the top of the footings and grade to accommodate the pipe, drain rock, fabric, downspout drains, and some material to cover it all.

  2. Brian Adams | | #2

    Yes, that's the hard part. Due to the amount and depth (or I should say shallowness) of rock, there are points where the footings are all but exposed. There are a few spots where I might have 18", then there'll be the next footing step and I'll be back up to 6".

  3. Expert Member
    Malcolm Taylor | | #3

    Brian,
    It's a bit late for you, but generally in those circumstances it's best to raise the top of the foundation, or lower the rock. Neither option is particularly palatable, but if you don't end up with a sufficiently high foundation wall, you end up with the problem you are facing now.

  4. GBA Editor
    Martin Holladay | | #4

    Brian,
    Malcolm is giving good advice. If you have a tricky sloped site, there are three ways to address these difficulties with footing drains:
    (1) Raise the foundation by adding another course of concrete blocks;
    (2) Raise the exterior grade by moving around some soil (or hauling in some purchased soil if necessary; and
    (3) Raise the interior grade (the floor of the crawl space) by adding gravel or sand.

    The most trouble-free crawlspaces have a floor level that is above the exterior grade.

  5. Expert Member
    Peter Engle | | #5

    I would also mention that the rock itself can be a water problem. On a sloping site, any low spots, cracks and similar features in the rock can channel water from uphill and under your garage, emerging in the crawl space. Cutting a swale in the rock on the uphill side would be a good idea, or at least cutting through any significant ridges so that you can install outside perimeter drains below slab level.

  6. Brian Adams | | #6

    Ok, waterproofing is done. There are only two portions of uphill facing wall that is unprotected by the garage, I put a lot of effort on those spots. Since I waited so long there was some dirt buildup on the footing, very difficult ( impossible) to clean to allow a really good connection with the sealant from block to footing. I did my best.

    The entire backside of the house is both protected by the garage placement uphill and with what will be a 10' over hang over the back porch. The soil there should never get wet. It got some waterproofing for good measure.
    The front will have nearly a full surround porch as well, again offering protection.
    And with so much of the immediate perimeter of the house being protected and covered by porch, I don't necessarily have to backfill those spots. This would help keep the interior grade higher than the exterior. Am I right in this or off the mark?

  7. GBA Editor
    Martin Holladay | | #7

    Brian,
    Before anyone can give you advice on backfilling, you need to tell us your geographical location or climate zone. One reason for backfilling is to protect the footings from freezing.

  8. Brian Adams | | #8

    CZ-4A, Chattanooga, TN.

  9. GBA Editor
    Martin Holladay | | #9

    Brian,
    I'm not sure how deep you need to bury footings in Chattanooga. Just make sure that your footings are backfilled enough to protect them from freezing -- if you don't know how deep they have to be in Chattanooga, ask local contractors for advice.

    The fact that you have a garage on the uphill side of your house is no guarantee that the soil on the uphill side of your crawlspace won't get wet. In late winter or early spring, soil can get saturated, and natural underground springs are always a possibility.

    If you know that your crawl space is dry, that's great. But plenty of crawl spaces installed on a hillside (with or without a garage on the uphill side) have water entry problems due to wet soil on the uphill side.

  10. Brian Adams | | #10

    I've decided to bite the bullet and have my builder do a proper job waterproofing the crawlspace.
    Thank you all for the input. I'm sure I'll be much more pleased with a dry crawlspace!

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