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Thread: Cabin Foundation Advice Needed

  1. #1
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    Default Cabin Foundation Advice Needed

    I will be building a cabin on Kodiak next summer and am struggling with foundation decisions and need advice. If access and time was not a problem, then I would dig down below the frost line and pour a concrete foundation, etc, but this is water only access and I also want to get the footings in place quickly so that I can get the floor started this trip. I can have Sakrete delivered to the site by the pallet along with a 2 or 3 bag mixer and will also have use of a backhoe. From my reading I see the following as possibilities, vertical piles set in concrete footings below frost line, sonotube version of same, concrete block version of same, and wood pad and cribbing methods I saw referenced here. I have lots of questions about how each of the above would best be done in this setting. Add that I have built lots of pier and beam buildings but am not familiar with building north of the Mason Dixon line so am not sure what frost heave, etc. is or looks like. Thanks in advance for any suggestions and resource recommendations!!

  2. #2

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    When we built our cabin north of Anchorage, I didn't want to spend the money on pouring footers and then using sonotubes. I had a buddy cut piles out of 7" casing and weld a 2' x 2' steel plate on the bottom as a footer. I dug holes with a backhoe and dropped them in. Getting them alighted precisely was difficult but I made sure they were aligned within the diameter of the pipe so I could move the joist brackets back and forth to line them up and also that they could be adjusted with jackscrews to get them level.

    We filled most of the tube with gravel and topped off the last foot with cement mostly to keep the joist brackets in place.

    We did this over 15 years ago and haven't had a problem since. This might be a more costly solution than sonotubes but if you have access to junk casing and steel plate and a welder, it could be a good solution.

    If you don't do something like this, you will definitely want to use sonotubes to eliminate frost jacking.

  3. #3

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    The first thing I would do is contact some folks on Kodiak and find out how they made thir foundations and what has worked. And also ask what the frost line is there. I'm guessing it's been done more than one way. I would recommend the sauna tubes about a foot or so in diameter with about four 1/2 sticks of rebar in each. It would be good to have about a 2'x 2'x 8" thick footing under each sauna tube with some rebar also, and rebar sticking up out of the footing to tie in the sauna tube concrete pier. You should place about 6 inches or more of gravel under your footings. The less water you use in mixing you concrete the better - less water means stronger concrete. You could build a *floating* foundation and put piers near or at the ground surface, but frost heave is a very powerful force and if you get uneven freezing and thawing, lifting and settling your doors and windows will likely start bindng on you.

    Have fun with your project.

    Cheers,

    Mark

  4. #4
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    Thanks, and I have a few more questions (more than a few) and thoughts on any of the following would be helpful and appreciated. The welded poles idea sounds quick and good, but unfortunately I don't have advance access to a welder to fabricate anything and the materials have to be stock items delivered to the dock and placed on the beach before I get there.

    Assuming its a 40 inch frost line (I will check that- so far dont see anything published on it), then I assume that I just have to get below 40 inches (do you have to put the entire thickness of the footing or pad below frost line- does that matter?).

    As to sonotube method, I assume this is correct and can be done in one pour if possible- gravel in hole, followed by rebar and 3 or 4 bags of Sakrete, then stick the sonotube into the wet concrete, plum and brace, cut tube to correct height above grade, put in rebar, and then fill up the tube? As to concrete strength, its twice as expensive but we are talking about 8 to 10 footings so is there anything wrong with using quickset?

    If delivery of concrete block is not an issue- is there a frost issue on using them (blocks on top of footings) and are they commonly used?

    I like the simplicity of a vertical piling foundation, creosote poles or ties stuck in a puddle of concrete and later cut at correct height with chainsaw once concrete is cured, but is that common as well? I assume that it would last a long time, but I like to overbuild and don't want a permanent cabin with a temporary foundation.

    Finally, I can't quite understand what is meant by floating foundations. Have seen drawings of peices of creosote beams or ties stacked in large holes like cribbing, alternating with rocks at each layer, and which are stacked up to above grade then backfilled, with beam strapped to it above grade. I have also seen drawings of wooden pads just placed on grade. Are these "floating" foundations? These seem relatively easy- at least no mixing of concrete by the bag, etc, but are they really used unless you are trying to avoid permafrost issues, which I won't have?

    Thanks for the help.

  5. #5
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    Quote Originally Posted by ehb View Post
    Assuming its a 40 inch frost line (I will check that- so far dont see anything published on it), then I assume that I just have to get below 40 inches (do you have to put the entire thickness of the footing or pad below frost line- does that matter?).

    As to sonotube method, I assume this is correct and can be done in one pour if possible- gravel in hole, followed by rebar and 3 or 4 bags of Sakrete, then stick the sonotube into the wet concrete, plum and brace, cut tube to correct height above grade, put in rebar, and then fill up the tube? As to concrete strength, its twice as expensive but we are talking about 8 to 10 footings so is there anything wrong with using quickset?

    If delivery of concrete block is not an issue- is there a frost issue on using them (blocks on top of footings) and are they commonly used?

    I like the simplicity of a vertical piling foundation, creosote poles or ties stuck in a puddle of concrete and later cut at correct height with chainsaw once concrete is cured, but is that common as well? I assume that it would last a long time, but I like to overbuild and don't want a permanent cabin with a temporary foundation.

    Finally, I can't quite understand what is meant by floating foundations. Have seen drawings of peices of creosote beams or ties stacked in large holes like cribbing, alternating with rocks at each layer, and which are stacked up to above grade then backfilled, with beam strapped to it above grade. I have also seen drawings of wooden pads just placed on grade. Are these "floating" foundations? These seem relatively easy- at least no mixing of concrete by the bag, etc, but are they really used unless you are trying to avoid permafrost issues, which I won't have?

    Thanks for the help.
    In anchorage we have to go 42" below the frost line by code, for foundations. For sonotubes we usually place 6-12" gravel then the tube, level it then pour concrete then place J bolts. Block is not a common footing material here, though it is used. If using crosties or power poles I have seen them used without the concrete, but you might get more movement with this system. Be sure that you use a frost break in the active frost layer, wrapping the pole with plastic from the ground line to the bottom of the frost line will keep the frost jacking to a minimum. Floating foundations are ones that allow the building to move with the seasons. If you don't mind an unlevel floor, or re-leveling 1-3 times a year tis works fine. Also no one mentioned Helical foundations. With a backhoe you could install them in no time. They cost 1-3 thousand a piece but you could install all 8-10 in a day or two. Below is a supplier in eagle river and their phone number. The web link is to the brand of helical foundations they carry.


    ALASKA FOUNDATION TECHNOLOGY INC 907-694-3740
    http://www.abchance.com/helical-anchors.asp

    Also check out this old forum post http://forums.outdoorsdirectory.com/...dations&page=3
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  6. #6

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    Footings can or can not be used under the sauna tube. It just gives you a bigger footprint to prevent sinking and your soil bearing capacity would be a factor. I would put the footings in since it's a cabin to be lived in. You could pour them at the same time, but if you're hand mixing sacrete, just fill the footing stick some rebar in, put the tube on the footing and start filling the tube and stick some more rebar in. As you fill the tube, tap the sides and aggitate the concrete with a piece of rebar to get the voids out. I've never used quickset, so I cant comment on it. Sacrete should be fine and if you want increase the strength of it then buy a few bags of portland cement and throw in a half shovel for every bag of sacrete. Also, concrete that is exposed to freeze thaw cycles should be air entrained to prevent it from being deteriorated by freeze and thaw. Onr trick I've heard to air entrain do it yourself concrete is to mix a little dish soap in the water you mix into your concrete. You might also a local concrete batch plant to get their opinion.

    A floating foundation is basically a foundation system that rests on or slightly below grade (floating on grade) and is subject to frost heaving and settling. Moving with the seasons as garnede said.

    Hope this helps.

    Mark

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    You can also buy what is called a bigfoot for the bottom of the sonotube. It an upside
    down funnel. Basically a plastic form for the bottom of the tube that forms the footer. The tapered part is important, it helps keep the frost from lifting the pier.
    They come in different bottom diameters. One bigfoot will fit 3 different sonotube sizes.


    http://www.bigfootsystems.com/include/contact.htm

    Doug

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    You are not going to have the frost problems on Kodiak that we do on the mainland. Yes, it can get cold there, but not enough long enough to jack the foundation much.

    Sonotubes on top of BigFoots buried 48" will be more than enough for a small cabin.

    You can buy BigFoots from Spenard Builders..if they don't stock them in Kodiak they can get them quickly. Are you building within city limits? I'm sure they have some sort of building codes out there. Best to check.
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