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Trimming a house with a sinking basement slab

john_bowne | Posted in Construction Techniques on November 13, 2023 06:36pm

My sister lives in the suburbs of Denver. She has a small house that was likely built in the 70’s. The house was built in an area that has expansive soils. Apparently, the exterior concrete foundation was tied to bedrock with some piers. However, the slab floor of the basement was left to float on top of the soil. In the first 10-15 years, the slab moved up and down, seasonally by about an inch. Recently, a neighbor had some remodeling done that involved some heavy equipment running up and down on the property line. The slab on that side of the house has dropped an additional 1-2″.

I’ve been trying to help her finish the basement, but with this gap, I’m running out of ideas. The bottom plate of the walls has a gap of 2-3″ now.  It seems that the practice has been to fasten a 2×4 to the concrete, then rest the double bottom plate on it. Then using a 6-8″ spike, to give the wall some lateral support, with a inch or two between the top of the double plate to the underside of the head. With the recent movement, most of the spikes have used up the slack and are now lifting the plate off the floor or the spike as lifted clear. 

Likely, the best temporary answer is to get someone to do some mud jacking, but the $60K estimates are out of her price range, being a government worker. 

I’ve been looking for a way to at least trim out the walls, so there are 2-3″ gaps at the base.

Also, just wondering what all of this motion is doing to drain lines. 

Any thoughts?

    johnbo

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Replies

  1. 1095mike | Nov 13, 2023 08:07pm | #1

    maybe a soil test?

  2. jameswbush | Nov 15, 2023 01:29am | #2

    You can try using metal brackets or shims to fill the wall gaps temporarily. Keep an eye on the drain lines for potential issues and consider getting a professional opinion on the foundation when possible.

  3. calvin | Nov 15, 2023 09:04am | #3

    John,
    My first encounter on moving basements was on this forum a long time ago. If you search here any key word you can think of, you might get lucky with an answer.

    Commercially I found metal deep throat track was used at the top of a wall to allow the stud wall (shorter)the room to slid up/down while still being trapped in plane.

    This won’t help you now but it stuck an idea in my head. Not thinking it’ll interest you nor even work…..

    2 pc baseboard, one over the other with room to move, ie. one glued to the floor with (PL Premium adhesive), the other fastened to the wall and rabbited so the one on the floor slides up/down behind the one basebd fastened to the wall.

    Now that you’re done laughing……

  4. john_bowne | Nov 15, 2023 12:14pm | #4

    Sorry, work took over for some days.

    A soil test has been done and amounted to "Yeah, all of the houses in this area have the same issue".

    Regarding the metal brackets (from jameswbuch), my concern has been trying to finish the sheetrock when the length of the wall keeps changing.

    I do like the idea of the 2 pc baseboard, as long as the wall can stay aligned with the spikes, or replace them with longer ones, this might work for this application. I was toying with a similar idea, but hadn't thought of the adhesive approach.

    I'm trying to visualize how the track brackets could be used, when trying to finish the wall, as there would need to be some way absorb the movement, short of a very large cornice molding, to avoid a gap at the top. It does solve the drain problem, but might now cause a plumbing problem, unless PEX was used to make an isolator from the basement plumbing to the upstairs plumbing.

    Something is definitely going on under the house. There was one area of the slab, that if I jumped slightly on the concrete, things would rattle a couple of feet away. Makes me believe that the slab is not done dropping and the mud jacking MIGHT help, assuming that the soil is not flowing out underneath the foundation.

    Thanks,

    1. calvin | Nov 15, 2023 06:09pm | #5

      I don’t envy your situation.
      For the top of the wall since you couldn’t use the deep metal track, perhaps there’s an angle available with a long and short leg. A crown or even a flat trim to cover.

      Are these walls finished, Sheetrock done?

  5. john_bowne | Nov 16, 2023 06:01pm | #6

    Yes, all of the walls have been finished with sheetrock and paint.

  6. stamant | Nov 16, 2023 09:51pm | #7

    -- might consider anchoring the studs with roof truss clips such as simpson STC to provide some lateral support.

    --regarding the gap at the floor, you have a piece of ell-flashing attached to the floor and floating on the wall. then have a piece of tall baseboard attached to the wall above the flashing. The slab could move up and down without a visible gap -- the reveal would just change between the wood trim and the metal angle.

    test for radon levels if it's an issue in the region. sounds pretty open to the earth.

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