Results 1 to 11 of 11

Thread: Advice on Sonotube foundation HELP

  1. #1

    Default Advice on Sonotube foundation HELP

    Let me start with the fact that I am brand new to building. I built a chicken coop and that's it. This summer I am building a 16x20 cabin on my land in Willow. 2 weeks ago I went and dug 9 holes with a hydraulic digger about 4' down. I used 4'x8" sonotubes and filled with concrete. I placed a J bolt in each one to attach a bracket for holding the beams. So 3 rows of 3 tubes each, Then laying a 20' 4x12 treated beam across each one. Creating a three 20' horizontal beams spaced 8 feet apart. So I created a platform to lay my subfloor on. I plan to attach the subfloor to the beams with thread rods later on.

    THE PROBLEM. After I poured the tubes I realized I should have made the footings wider by adding bigfoot footings or at least belling out the bottoms and lifting the tube after the pour. This would prevent jacking and also provide more weight distribution...Well too bad I didn't think of that when I poured them. SO they are 8" wide and have 42" below ground...leaving the top 6 inches or so above grade. My Question is what to do now!? I have sandy soil with a touch of clay/silt...hard to tell, but mostly sand below the 12 inch line. Well drained area...sits up higher than everything around it. Large birch and white spruce trees present. No water pooled up in the holes even after that rain we just had.

    I have been told by a few local builders that "its no big deal...a cabin that size is fine on 8inch feet since I dug down so deep into undisturbed soil ...and unless its really wet/silty soil, frost-jacking would not be a problem either since I have good drainage."

    I figure I can do one of a few things..ONE: get a bumper jack and remove all the tubes from the ground...discard and start again with bigfoot footings and rebar...wasting all my time and money previously invested and then buying it all and doing it again...not fun. TWO: add a 4-6 more piers to increase my load capacity and hope frost jacking isn't an issue. THREE: Add more piers WITH bigfoot and rebar to stop jacking and increase load capacity...HOWEVER...Ive heard that having some piers anchored and some not is MORE of a problem because they will settle and heave differently. FOUR: LEAVE IT ALONE and see what happens...They are on j bolts so settling is an easy fix...jack up the cabin, raise the bracket and set back down. Ive been told jacking isn't always a major problem...maybe the cabin will be a little unlevel but it should still hold for years to come??? Not sure..OPINIONS??? Should I face the fact that I blew it and spend the 1000 bucks to do it again...or is it good enough for a little fishing cabin in the woods... THANK YOU
    Attached Images Attached Images

  2. #2
    Member .338-06's Avatar
    Join Date
    Apr 2006
    Location
    Anchorage
    Posts
    1,045

    Default

    I'd leave it alone. You could have easily gone with 4 tubes.
    I may be slow, but I get where I'm going!

  3. #3

    Default

    My math is as follows: load bearing capacity of my soil, im guessing, is between 2500-4500#psf...just a guess based on the high presence of sand. So let's say 3000psf to be safe (please correct me if I'm wrong.) With 9 footings each with an area 50.24 inches squared and a soil psf of 3000. That is roughly 1000lbs per pier. There is 9 piers...that means 9000lbs of support before I punch holes in the earth. Is a 16x20 half loft less than 9000lbs? With snow, weight of concrete, and at least 500lbs of beer!?!? I just don't know. Plus if I did exceed the bearing capacity, what is worst case senario? Cabin ends up on the ground?

  4. #4
    Member jojomoose's Avatar
    Join Date
    Sep 2011
    Location
    Anchorage
    Posts
    312

    Default

    Quote Originally Posted by mbrenna View Post
    My math is as follows: load bearing capacity of my soil, im guessing, is between 2500-4500#psf...just a guess based on the high presence of sand. So let's say 3000psf to be safe (please correct me if I'm wrong.) With 9 footings each with an area 50.24 inches squared and a soil psf of 3000. That is roughly 1000lbs per pier. There is 9 piers...that means 9000lbs of support before I punch holes in the earth. Is a 16x20 half loft less than 9000lbs? With snow, weight of concrete, and at least 500lbs of beer!?!? I just don't know. Plus if I did exceed the bearing capacity, what is worst case senario? Cabin ends up on the ground?

    First off, great blue prints. Is that toilet paper?

    Second I would also leave them, you have to remember you are building a cabin not a sky scraper. you will be good, you will have some heaving but most cabins do anyway. Just use venear or plywood instead of sheet rock, it won't crack that way.

    Joe

  5. #5
    Moderator bkmail's Avatar
    Join Date
    Apr 2006
    Location
    Palmer, AK.
    Posts
    4,121

    Default

    Quote Originally Posted by jojomoose View Post
    First off, great blue prints. Is that toilet paper?

    Second I would also leave them, you have to remember you are building a cabin not a sky scraper. you will be good, you will have some heaving but most cabins do anyway. Just use venear or plywood instead of sheet rock, it won't crack that way.

    Joe
    Agree with Joe, your cabin will be just fine as is.
    Bk

  6. #6
    Member
    Join Date
    Jan 2015
    Location
    Southcentral Alaska
    Posts
    567

    Default

    I would just make sure that I built in an easy way to lift, level and shim the cabin, in case of differential movement. You will be fine.

  7. #7

    Default

    Well I am very pleased to hear all the votes to LEAVE IT ALONE. Thanks for the feed back everyone. I think ill call it good and start building. I will be able to jack and shim very easily with my set up.

    HAHAH yes...Napkin blue prints...gotta make due when posting from a restaurant on my iPhone hahah.

    I am going to do a french drain and overhanging ceiling to keep the water away from the tubes, as well as piling up lots of dirt and packing it around the tubes to they are as "deep" as possible. I am bringing the grade up to the tubes...haha might help...i dunno. Thanks again y'all

  8. #8
    Member akriverunner's Avatar
    Join Date
    Apr 2007
    Location
    wasilla
    Posts
    506

    Default

    You will be fine! I've definitely seen worse situations than what you say you have. Like mentioned above just make sure you can level it out if needed after a year of freeze/thaw cycle. Other then that I would do a two foot over hang on the roof and throw up some gutters to keep the rain away from the pilings as much as possible. Are you building stick frame or log? Also what are your plans for floor joists and subflooring?


    Sent from my iPhone using Tapatalk

  9. #9

    Default

    Thanks for the help on this one guys. I ended up adding a pier block in between each tube so my beams max span was only 5 foot instead of 10. Otherwise I risked failure...according to the computer at SBS. I am stick framing, I put in 2x8 treated joists 16" OC. Going to do a TnG OSB subfloor. 8 foot walls, premade Parallel trusses, 10/12 pitch so the loft is ROOMY...with open ceilings.

  10. #10
    Member 4merguide's Avatar
    Join Date
    Feb 2012
    Location
    Kenai Peninsula, Alaska
    Posts
    9,749

    Default

    Quote Originally Posted by mbrenna View Post
    I have been told by a few local builders that "its no big deal...a cabin that size is fine on 8inch feet since I dug down so deep into undisturbed soil ...and unless its really wet/silty soil, frost-jacking would not be a problem either since I have good drainage."
    If you haven't heard, another way to help against heaving is to make a few wraps of visqueen around the tubes before back filling. Believe it or not I learned this from a contractor that told me he was actually having a problem with is well casing heaving and breaking the line at the pitless. After repairing it a few times he was told to make the wraps with the plastic around the casing before he filled it back in. After that no problems. The dirt will grab the visqueen and the visqueen will slide against itself rather than the dirt grabbing the tube and lifting. Good drainage is a big plus, but anytime there is any dirt at all in backfills the potential for heaving will be present.

    Oh and btw.....what are you going to put over the osb floor? Whatever you use I'd make sure it will seal out any moisture because that osb will come apart if moisture has nowhere to go and allow it to dry out over any length of time. Personally I never use osb for floors just for that reason. Vertically applied is one thing, horizontally where water can puddle and stay is another. They don't call it "(O)h (S)hi**y (B)oard" for no reason.....lol. Although a bit more expensive, CDX is better for floors.....imo.
    Sheep hunting...... the pain goes away, but the stupidity remains...!!!

  11. #11
    Member 4merguide's Avatar
    Join Date
    Feb 2012
    Location
    Kenai Peninsula, Alaska
    Posts
    9,749

    Default

    Quote Originally Posted by mbrenna View Post
    10/12 pitch so the loft is ROOMY...with open ceilings.
    You may want to wire in for a ceiling fan up there......
    Sheep hunting...... the pain goes away, but the stupidity remains...!!!

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •