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Thread: Cabin Foundations?

  1. #1
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    Default Cabin Foundations?

    I am planning on building a small cabin this spring on the Kenai Peninsula, after I haul in all of the building materials over the winter. However I am undecided on how I am going to make the foundation. Any ideas from those guys with experince with this sort of thing? What has worked for you in the past?

    Thanks in advance,
    JB


    Plan on building 12x16 cabin.

    No Perma Frost.

    Wet soils... closer to silt/mud than sand.... seems to be bottomless, to at least to 4' down. Test post holes started to fill with water after a few minutes, level of water was about 18 inches below surface(???).


    #1
    I am leaning towards:
    Sinking pressure treated posts down about four feet. Wrapping with plastic to prevent heaving. Backfilling with what I dug out of the hole. Deal with settling as it occurs.


    #2
    Haul in premix concrete. Use sono tubes. Back fill with what came out of the hole.


    #3
    I have heard of this:
    Digging a hole 24" square to a depth of 16". Back fill with gravel/crushed rock. Lay down concrete pavers and place pyramid shaped concrete block on top of pavers. Not sure if this will heave???


    I would like to stay away from #2 & #3 because I have to carry every thing 300 yards. I don't think I can get up the bank with snowmachine, hope to find out when we get some snow.

  2. #2
    Member JOAT's Avatar
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    Default

    Quote Originally Posted by jrb View Post
    Sinking pressure treated posts down about four feet. Wrapping with plastic to prevent heaving. Backfilling with what I dug out of the hole. Deal with settling as it occurs.
    I can tell you that this idea probably won't work and 4' isn't nearly enough depth. I used to have a deck off the back of my house (came with the place when I bought it) where they used treated posts wrapped with plastic for the outer supports. I'm on dry, level forested land and the outer edge of the deck (over those posts) would heave nearly a foot between summer and winter. I replaced the whole deck and when I pulled up those posts, the plastic did nothing more than hold water so the bottom of those posts were completely water logged. It was the worst idea I ever saw. On my new deck, which is over 3 times larger than the original, I used sono tubes and it hasn't moved an inch since.

    To prevent heaving, the pyramid shaped base will work better than a cylinder, but since it sounds like you're building in a swamp, you've got other issues. If there is any way to drag a pile driver in there you could sink some steel pilings down into solid soil. Short of that, you may be able go down 6' or better with sono tubes... depending on how fast the water comes in. A gas powered earth auger might help you out and they are portable.

    I've never built anything in that kind of soil, so hopefully others will have some more specific recommendations.
    Winter is Coming...

    Go GeocacheAlaska!

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    Default hmmmm..

    Good thing I have all winter to come up with a plan!

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    Moderator Daveinthebush's Avatar
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    Default My place

    My place is actually two warm-up cabins left over from the oil spill, nailed together. That said, it was originally sitting on 56 railroad ties and five rail road rails. What a mess. And a few footers.

    It used to be about 24 x 30 but grew 9 feet to about 32 x 30. The soil was gravel, someone hauled in a lot of fill. As I started leveling, I found that I could raise the entire front by jacking one rail and it never bent at all. So I left them under. I poured four footers under each rail, 6-8" deep and 2' x 2' and piled double rows of concrete blocks until I needed wood spacers and leveled. I must be about 3 foot above firm earth. I cut the rails off of one end as they stuck out. The other end they stuck out 6' so I left them. Two years latter, I added footers under those rails and added a full length porch.

    I have not had to level the place in two years. I do experience some heaving at times but not much. Just letting you kow what I did. Swampy earth you may have to lay down a gravel pad first as they did here.

    Vietnam - June 70 - Feb. 72
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  5. #5

    Default Old timer advised me.

    I have a 24 x 28 ft. cabin sitting on steel pilings that were driven down 9'. It still moves occaisionaly.

    A good friend that grew up here on the Kenai Peninsula, (family was one of the original homesteaders), advised me to not do anything for smaller cabins. He has built many cabins, most are smaller, like the size you stated.

    For those he puts down railroad ties and builds on them. His theory is the cabin will float with the ups and downs. Occasionally he breaks out a jack and levels it up. Once in the summer and once in the winter. For an hour each time to jack the savings are worth it. IMO

  6. #6
    Member garnede's Avatar
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    You need to decide if you are willing to accept a un-level floor. If you are then you should go with a skid design and let the cabin float on the surface. If not then you need to drive piles. Wood will work but steel or concrete is better. If you go with wood use treated at the least and creasote(sp) at the best and DO NOT wrap in plastic. It will eventualy get water traped inside the plastic, usualy a week or less, and then hold the water against the wood. Also 4' is too shallow for wet soil. Here in Anchorage with well drained soil foundations are that deep or deeper to prevent frost from heaving the concrete foundatins out of the ground. On wet/weak soil you need to co much deeper. Preferably untill you hit solid ground, but you should see 10' as a minimum so that the friction between the ground and the piling will pervent you from sinking too fast.

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    Member Ripper's Avatar
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    Default

    It sounds like this site is relatively inaccessable to larger equipment? If pile driving isn't an option, I'd create some kind of a skid/mat/pad that would "float", but be resistant to much twisting. In fact, I'd probably do that over pilings anyway. In that wet of a situation you may experience some movement even with 10' piles. It is easier to design a pad with jack attachment points and just level as you need to. I like the rail idea, but I-beams will work too. The key is to make something rigid enough such that when it moves and you jack it, it moves as one piece. Just my 2 cents...

    I'm in Sterling...if you want to chat more about it, shoot me a PM.

    Ripper

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    Moderator Daveinthebush's Avatar
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    Default Actually

    Actually when I was living in Elim they built the jacks right into the foundation on the permafrost. Pads, pilings, jacks, beams w/ house on top.

    You might be able to find some cheap screw adjust bottle jacks and build them into the design, or some support posts with screw adjustments.

    My porch has the triangular concrete pads with a connector and a screw adjustment. Pretty simple to lay a level on once a year and adjust with a Crescent Wrench. You can even buy cheap levels (RV or camper)and permanently attach them to certain points of the cabin so a quick look and you know if it needs leveling.

    Vietnam - June 70 - Feb. 72
    Cancer from Agent Orange - Aug. 25th 2012
    Cancer Survivor - Dec. 14th 2012

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    Member Dirtofak's Avatar
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    Default

    If anyone has any pictures or drawings etc of adjustable piers I would be very grateful.

    Jacking and blocking just doesn't appeal to me.

    Thanks,
    Mike

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    Default Screw anchors

    These are the words of U-Bob and a pic of his neighbor down on the Peninsula:

    "As all you bush rats know the method of wraping your treated posts in poly or visqueen is a well proven method widely used. We did ours that way over 20 years ago and they are still doing good. The only problem is whatever you use for fondation over tundra it will settle.
    There is a new guy on the block in our neighborhood and when he first showed me his method I was very skeptical but have become a believer after I got involved as a sidewalk superintendent with his construction. Basically it is a modified auger that screws into the ground and the upper tip has an attachement fitting for your support beams to set on. It also has very long threads on the auger so WHEN your foundation settles you can easily adjust it. The augers are cheaper and lighter than pressure treated lumber and if you get lucky the auger ended up like theres setting on light gravel and rock at about 5'. When the augers were first set they didn't seem very sturdy to me but once they were locked together with the beams and then the joists they were very sturdy.
    He also used blueboard around the entire base of the foundation for insulation. All in all a very well done job. Will be interesting to see how it works over time but it looks very promising to me.
    The problem out here in the rural areas is we have our head in the sand and we need new blood to inject something new." End of quote.

    U-Bob's health is declining, he never got back with more info. The picture however gives a guy a good understanding what he is referring to. If you read this Bob - get well soon!

    Gord


    "He was a man of no patience, you could see it in him. That was a notch against him. In the wild country, a body needs patience".

  11. #11
    Member garnede's Avatar
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    Default

    The proper name is Helical Foundations. I have seen them used for the foundation of a 100' fire tower before on the edge of a swamp. I am not sure about adjustment though. If you use the large machine designed to "screw" them into the ground then they can be deep enough that should be no worry about adjustment. The great thing about these foundations is no concrete.

  12. #12
    Moderator Daveinthebush's Avatar
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    Default Thest may work too.

    These might work too. It would only take a little bit of metal working skills to make up a set.

    http://www.ellisok.com/ellisok/products_screwjacks.html

    Vietnam - June 70 - Feb. 72
    Cancer from Agent Orange - Aug. 25th 2012
    Cancer Survivor - Dec. 14th 2012

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    Member Dirtofak's Avatar
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    Anyone have a source for the beam cradles and threaded adjusters (like in the pic)? I can weld up a base.

    Mike

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    Default Thanks for all the info

    We will not be living in this cabin, so a little bit of movement is acceptable. It will be basic... only a wood stove. Might wire it for a generator down the road.

    Jacking it up to level or incorporating screw jacks into the foundation is a reasonable expectation for us.

    Sounds like posts in this soil type may heave no matter what. So I will try and learn a little bit more about the various pad / skid ideas.

    Keep the ideas coming.

    Thanks,
    JB

  15. #15
    Moderator Daveinthebush's Avatar
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    Default Suggestions

    Quote Originally Posted by dirtofak View Post
    Anyone have a source for the beam cradles and threaded adjusters (like in the pic)? I can weld up a base.

    Mike
    If you know the width of your beam, you might be able to buy some channel iron and have the supplier cut it into 8 - 12" sections. There are many lengths, widths and thicknesses out there. They would probably use a horizontal bandsaw so the cuts should be good. Sometimes paying for someone elses time is cheaper than your time when they have the right tool.

    Another option is to use two pieces of angle iron and weld the edges together to form the U.

    If you don't need a U shape, a simple L should work if you bolt through it into the beam. Again, lots of widths and thicknesses out there.

    Vietnam - June 70 - Feb. 72
    Cancer from Agent Orange - Aug. 25th 2012
    Cancer Survivor - Dec. 14th 2012

  16. #16

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    Quote Originally Posted by dirtofak View Post
    Anyone have a source for the beam cradles and threaded adjusters (like in the pic)? I can weld up a base.

    Mike
    Google up Chance Anchors or Chance Anchoring Systems. They can't be beat.

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  18. #18
    Member Queen of Kings's Avatar
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    Default If you can weld?

    Quote Originally Posted by dirtofak View Post
    Anyone have a source for the beam cradles and threaded adjusters (like in the pic)? I can weld up a base.

    Mike
    I could'nt find anthing without specail orders, and they still were not what I wanted. So, I took some 4" x 6" x 1/4" wall box tubing, cut of the one top part, to leave basicly 4" x 6" "U" shaped braket 12" long, drill holes through the sided for lag bolts, welded some 1" all thread to the bottom. Then I drilled 1 1/8" holes into the vertical post for the all thread to fit into, then used 1/4" x 6" x 6" alum plates with a 1 1/8" holes for the large washer on top of the post, used standard 1 1/8" washer with anti-sieze on top od that. My 4" x 12" beam sits i this saddle and I have all the adjustment and strenght I need
    2003 220 Hewescraft Sea Runner 115 Yam'y, Soft Top "Schmidt Happens"

  19. #19
    Member SuYentna Dave's Avatar
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    Default Screw Jacks and Sonatubes

    Your Foundation is the one thing you want to do only once. Take it from a guy that has redone my twice.

    The first time was built on natural timbers cut with a alaska chainsaw lumber mill, painted with weatherproofing, coated with roof tar and wrapped in visqueen. They last 8 years and when I replaced them they was complety dry rotted. Wood ants got into them and had breakfast, lunch and dinner.
    The Second time I did it was with replacing the posts with railroad ties. Talk about some heavy piss of ...wood. They lasted pretty good but when I put a addition on they started to split.

    I dug out and put in sonatubes , hauling in 60 lb p-mix sacks and set the screw jacks in. The cabin is rock solid and if I get a low spot it takes very little effort to level the cabin up. White spruce trailers had some screw jacks that work well as things settle.

    Remember your foundation is like that Fram filter...pay me now or pay me later

    Good Luck

  20. #20

    Default Screw Jacks

    The brand White Spruce sells are anchorposts. Here is the link to their website:

    http://www.whitespruce.com/anchorposts.htm

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