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Thread: Need advise on a foundation

  1. #1
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    Default Need advise on a foundation

    We finished our dirt work over the summer and have a nice level pad for a 18 x 24 cabin. There is about 12" of schist over bedrock, and we have great drainage. No evidence has been found of permafrost. We will be building on piers with leveling screws on top. We were thinking of pouring a 36" square reinforced slab about a foot thick under each pier. Now thats over kill for the weight but I have no clue about frost heave. Does this sound ok or do i need a diffrent plan

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  2. #2
    Member cdubbin's Avatar
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    Sounds skookum enough....if it truly is rock, you're good to go...only fines will heave much, and only under very certain conditions.
    " Gas boats are bad enough, autos are an invention of the devil, and airplanes are worse." ~Allen Hasselborg

  3. #3
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    If that bedrock is hard, dig down to it and take hammer drill and install concrete anchors into the rock. Spin a piece of threaded rod into the anchor and place a sonotub over it and pour a concrete pier. Wouldn't be hard to do and you'd have a pretty good foundation for the cabin. Rock won't frost heave.

    Now, if you can chip apart the bedrock with a pick, that's different.

  4. #4
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    All my pads are 2' X 2' X 6". I've built half a dozen 16x24 cabins with each pad 8' apart. A couple were on permafrost and moved an inch or two in the first couple of years. Very easy to level as needed if you have a couple of feet between floor joists and the ground. 1 foot thick is definitely over kill for that size cabin especially if you are so close to bedrock. Nothing is going to stop frost heave if it is under your foundation. That looks a lot like the Steese Highway area. I saw a lot of water oozing out from under the moss into and above the roads in the River view subdivision. Mostly black spruce in the burned area which indicates permafrost but lots of rock showing also. Make sure you have good drainage away from your footings if there is a chance of water coming in from above.

  5. #5
    Member ChugiakTinkerer's Avatar
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    Pad and post construction is usually chosen when soils are so bad or permafrost is a concern. Since you have bedrock so close you can anchor your foundation directly to rock and take the 12" of schist out of the equation.

  6. #6
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    a1shiva has it nailed. Pads are fine, but if water is surfacing or a sub-surface issue nothing will stop it from freezing and heaving in the winter. It's surprising how water can spring from the ground at high elevations. Use typical pads but allow for jacking and leveling in your design

  7. #7

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    I agree with the above comments, anchor into the bedrock and pour your pads directly on it. Just dont leave to much threaded rod hanging out the top, they can lay over with a slight change. Seen it happen a dozen times or more. Personally in that situation I would pour the pads on the bedrock, and just use blocks to hold the cabin up, it isn't going anywhere and is only a jack and a shim away from fixing down the road. You can also cable spring it so it keeps constant pressure to keep everything square, helps with re leveling and if the cabin tries to slide off one side for some reason.

  8. #8
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    God i wish i had some water on my place its dry as the saraha. However i will go straight to the bedrock. We used a D6 and dug the pad down to the point where the dozer would stall or slide sideways lol. The rocks we were able to dislodge were the size of car engines, they were the small ones. We used the schist just to level out. I am indeed in riverview on the steese, good eyes A1shiva. Thanks for the help folks!

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  9. #9
    Member DRIFTER_016's Avatar
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    I have good bed rock at my site and have done as others have suggested and pinned to the rock.
    I am using 6X6 and 8X8 PT piers attached to the rock with galvanized saddles that are installed with non-shrink grout.

    Here are a few images of the work.
    I have built it with a good sized "crawl space" with double doors for access.
    Will be great for storage and I can actually drive a side by side in there to keep it out of the weather.
    Perfect for the sleds, ladders and I will store my pellet supply for the stove under there as well.






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