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Thread: Big Log cabin foundation suggestions

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    Default Big Log cabin foundation suggestions

    I'm building a 30 x 25 log cabin on the Deshka River. The foundation is my project for this summer. I've had a lot of suggestion from many different people, but still haven't decided to do an underground pier foundation or an above ground footing / pier foundation. At this time I'm leaning towards above ground footing i.e. Big Foot Forms. I'd like to hear from you doer's out there.

    I'm working on sand / gravel and usaully a layer of clay. The site has very little slope to it. Thanks

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    Member Dirtofak's Avatar
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    Go talk to Lyle at AAA Fence in Anchorage. He knows big log homes. His is on piling and it is HUGE! His company drives piling at remote places.

    Mike

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    A building of this size on that terrain needs 8 Chance Helical Piers. Anything less would be inadvisable.
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    Quote Originally Posted by GrimeyAK View Post
    At this time I'm leaning towards above ground footing i.e. Big Foot Forms. I'd like to hear from you doer's out there.

    I'm working on sand / gravel and usaully a layer of clay. The site has very little slope to it. Thanks

    Those Big Foot Forms normally go underground. Dig a hole, drop in the big foot form with an appropriate length sono tube attached to it, and fill em up with concrete. The wide base on the form spreads the weight out over a larger area of soil and the concrete pier (the sono tube) transfers that weight from the building down to the base.

    How deep is the clay? You really should have the footer below that clay layer.

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    The clay is pretty shallow 2'-3' down. I think I'm going to set the bigfoots just below the clay formation and sick with a 8' sonotube.

    20" big foot forms spead 4x4 ( totaling 16)

    That's 2.8 cu.ft of concrete / form and tube.

    thats 44.8 cu.ft concrete.

    67 bags(80lbs) Holy ****!!

    I was looking load spans for the beams and floor joist and I came up with 4x8 beams, and 2x10 joist @ 19.2" OC. Anybody see any problems with that.

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    Member cdubbin's Avatar
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    Have to know your beam span first; I'd go bigger than 4x8. Joists should be fine.
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    Don't waste your time on 19.2 o.c. it's a pain in the butt when it's all said and done. Just go 16" o.c.

    Your real strength needs to be around the perimeter. The row down the middle is only taking the flex out of the floor if you don't have any load bearing points.

    One issue with BigFoot forms is that if you space them narrower than 6' apart at 5 feet down you might as well just dig one long ditch. The material between the holes will just cave in anyway.
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    Default structures

    Anything short of full structural analysis may cost you more money in the future.

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    16 Big foot forms 24". 4x12 beams. Need to fab up some jack bolt brackets for beams. Going to be off the ground soon.

    https://picasaweb.google.com/lh/phot...eat=directlink

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    Quote Originally Posted by GrimeyAK View Post
    The clay is pretty shallow 2'-3' down. I think I'm going to set the bigfoots just below the clay formation and sick with a 8' sonotube.

    20" big foot forms spead 4x4 ( totaling 16)

    That's 2.8 cu.ft of concrete / form and tube.

    thats 44.8 cu.ft concrete.

    67 bags(80lbs) Holy ****!!

    I was looking load spans for the beams and floor joist and I came up with 4x8 beams, and 2x10 joist @ 19.2" OC. Anybody see any problems with that.
    With the 19.2" joist spacing it appears that you plan not to stagger joints in the subfloor. That might be a mistake. Will 16" or 24" be too much a problem for you for some reason ?

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    Quote Originally Posted by AKDoug View Post
    Don't waste your time on 19.2 o.c. it's a pain in the butt when it's all said and done. Just go 16" o.c.

    Your real strength needs to be around the perimeter. The row down the middle is only taking the flex out of the floor if you don't have any load bearing points.

    One issue with BigFoot forms is that if you space them narrower than 6' apart at 5 feet down you might as well just dig one long ditch. The material between the holes will just cave in anyway.
    ALL buildings will settle over time. The foundation pads at the corners only resist one-half the tributary load as do the others along the exterior walls. They should be somewhat smaller to eliminate differential settlement !!!

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    I think you missed my point... the row of posts down the middle of the floor, not the middle of the outside perimeter.

    With proper sizing and construction, that difference in settling on perimeter posts will be minuscule. There is also NO WAY to calculate how much settling each post is going to see, so it's not worth the time to even try to figure it out.

    My biggest concern in Grimey's photo is that beam joint doesn't land on a post.
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    Default Big Log cabin foundation suggestions

    If you are already going to fab the brackets, I highly highly highly recommend building wood girders instead of using a typical 4x12 beam, which is totally crap in terms of strength and quality of the wood.

    Three 2x12s or four 2x10s (my preference) will give you FAR more rigidity and strength, be easier to haul and put (build) in place, and you can plan the length precisely. Stagger the ends of the individual pieces of lumber to split directly over separate interior sonotubes (I used four 10 and four 18 footers for each of my 28 foot girders), slab subfloor glue in between the boards, and nail together every 4 feet with 3 or 5 galvanized nails. Tar paper along the top and at the ends will keep your girders dry and sound.

    The entire span will be a single unit. Glulams accomplish this, but they are spendy, hard to move, and you can do better yourself. Mine are sitting on above ground footers, and bolted down with allthread that I secured to the rebar in each footer and ran up through holes drilled in the girders. So no brackets with mine, but you will have to build the brackets just over 6" wide to accommodate 4 2x10s, which is why I mention this.

    Consider it.

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    Default Big Log cabin foundation suggestions

    Ouch, looked at the photo and see you already have your beams. Oh well. I share doug's concerns, but as long as each individual beam rests on at least two footers you should be ok. Not great, but ok.

    I also disagree with downsizing the corner footers. If the building moves, it has to start at a corner to do so, and thus your corners need to be as stout as possible, with everything tied together from footer to rafter.

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    Quote Originally Posted by AKDoug View Post
    I think you missed my point... the row of posts down the middle of the floor, not the middle of the outside perimeter.

    With proper sizing and construction, that difference in settling on perimeter posts will be minuscule. There is also NO WAY to calculate how much settling each post is going to see, so it's not worth the time to even try to figure it out.

    My biggest concern in Grimey's photo is that beam joint doesn't land on a post.
    Exactly what AkDoug said...also how deep are those sonotubes and how much is sticking out of the ground...

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    also in the pic although hard to tell that beam does not look plumb.... what are you using for connection points from sonotube to beam.. be sure to temp plumb while steeing anything on top to keep everything nice and plumb and square

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    Pics are deceiving. When I took pics of my footers this summer they looked totally messed up.
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    Andy- I have to disagree with your comments on 4x12's. They are graded just like any other quality lumber. The grading allows us to look in engineering manuals and determine the proper span for them. When you go to build-up beams you go into no-man's land. If not built properly they will not be stronger than a comparable sized solid wood beam. You have to follow design factors such as nailing schedule and glues to build them correctly. This info is not available, to my knowledge, without hiring an engineer for high load bearing span. I have found data that gives spans for interior floor beams. I do know that the recommended nailing schedule for 2x12's is 5 nails on 12" on center.

    If kept to the proper spans, 4x12's are good to go. They are also easy to handle with two guys on 20' long ones.
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    Quote Originally Posted by AKDoug View Post
    My biggest concern in Grimey's photo is that beam joint doesn't land on a post.
    Yeah......not good.....not ever, but especially for a heavy LOG home of this size.
    Sheep hunting...... the pain goes away, but the stupidity remains...!!!

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    If it's the internal beam to support the floor it may be just fine. Along the outside edge, not so much. The one thing a log home does is transfer loads down to the foundation completely differently than a framed house. You essentially have a stack of beams and ,depending on window and door cutouts, it can defy normal assumptions about how a pier style foundation acts. The logs are HEAVY though, and that cannot be ignored. Because of this weight, you have to be really careful about cantilevered floor joists.
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