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Thread: Good backcountry foundation?

  1. #1
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    Default Good backcountry foundation?

    I'm working up some plans to build a 16'x16' two story cabin next summer. The place is only accessible by foot and by snowmobile in the winter (so I'll be sledding all my materials out this winter). One old engineer told me that I should pour a wad of cement at the base and use sona tubes with Simpson bracket at the top. He said about 4 feet under grade would be sufficient.

    The other day, I talked to a young engineer. He said that I should only need to use green (treated) 6"x6" posts that rest on 24"x24" treated wood bases (2x12s 2 layers thick, and criss-crossed). He said that I should only need to go 2 feet down!

    The land is in Homer, and it's towards Caribou Hills, so It's colder than Homer proper, but still, it's no Fairbanks. There is crushed sandstone under about two feet of soil and sand. Pretty good drainage, although it seems to always be draining. Also there is a grade to the building site so one end will be about 6 feet up, and the other only about 2 feet up.

    What type do you recommend?

    Another question is, if I build a deck on the 16x16 structure, should I build it separate, or right onto the same beams that will hold my floor joists up?

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    Member Akheloce's Avatar
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    Where in the Caribou Hills are you? I have my place in Moosehorn subdivision, about a half mile south of Caribou Lake... I built my place on pier blocks (concrete cast in 12x12")





    I've had no problems in a full year.

    I posted earlier in this thread:

    http://forums.outdoorsdirectory.com/...ad.php?t=36692

    And nobody seems to think it will be a problem. The blocks are adjustable, so if I ever get any frost heaving, I can just take a wrench and move them up and down as necessary. In the full year it's been there though, there hasn't been any movement at all.

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    Member AlbertJohnson's Avatar
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    I'm getting to be an old engineer...but i like Aklehoce's method and the young engineer's method sounds fine too.

    Looks like Akheloce put his joist supports about 6' apart. That's a big key. You don't want those too far apart. 5 - 6' apart.

    I'd go with a separate front porch/deck. I've built about 40 decks in my life and always went this route.

    Good luck, sounds like you're in for a good and satisfying adventure. Nothing like a place you built yourself.
    Last edited by AlbertJohnson; 09-16-2008 at 16:13. Reason: more info

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    Member Akheloce's Avatar
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    One more thing... notice that the treated lumber I used is reddish brown... "green" treated lumber is for above ground use. The reddish brown stuff is "suitable for ground placement" They sell it at SBS, and all the other stores up north. IIRC, the price was comparable and cheap insurance.

  5. #5

    Default foundation

    I built my cabin like the young engineer said except I went 4' deep. My cabin is on Flathorn Lake. It is about 20 years old now, and everything is still really level. It was pretty easy digging so the 4' deep was not a problem. The 4' also helps to give it more stability sidewise.

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    Member AKDoug's Avatar
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    One more thing... notice that the treated lumber I used is reddish brown... "green" treated lumber is for above ground use. The reddish brown stuff is "suitable for ground placement" They sell it at SBS, and all the other stores up north. IIRC, the price was comparable and cheap insurance.
    Negative. Most green colored pressure treated is foundation grade and buriable. The incised red stuff is suitable for ground contact, but not generally for buried use. However, with well drained soils the red incised stuff will last a long time if buried.

    Look on the tags. If it says .60 FDN on it it is foundation grade. If it says .40 it is ground contact. If it is .25 and it doesn't have the incise marks it is treated decking. ACQ is the chemical primarily found on lumber brought into Alaska. On the end of the board will have a tag.

    Now, there are some cases where you will find .60 treated wood that is the red color. In my lumber yard I have the mill I buy from treat our 6x6 posts to .60, but I have them stain it red. That way the posts match the color of the deck boards and railings that I sell 6x6's for most of the time.

    My recommendation for posts generally goes like this. Observe a 2/3's 1/3 rule. If you are planning to have the posts stick up two feet, bury them 4' into the ground. The 24" 2x12 idea will work fine as long as you get the bottom of the hole nice and smooth. Make sure you cross brace between the posts or use plywood like Akheloce did on his place. I have seen several cabins eventually fall over if the posts are not braced.

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    Member Akheloce's Avatar
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    Quote Originally Posted by AKDoug View Post
    Negative. Most green colored pressure treated is foundation grade and buriable. The incised red stuff is suitable for ground contact, but not generally for buried use. However, with well drained soils the red incised stuff will last a long time if buried.

    Look on the tags. If it says .60 FDN on it it is foundation grade. If it says .40 it is ground contact. If it is .25 and it doesn't have the incise marks it is treated decking. ACQ is the chemical primarily found on lumber brought into Alaska. On the end of the board will have a tag.

    Now, there are some cases where you will find .60 treated wood that is the red color. In my lumber yard I have the mill I buy from treat our 6x6 posts to .60, but I have them stain it red. That way the posts match the color of the deck boards and railings that I sell 6x6's for most of the time.
    I stand corrected. The guy at SBS must not have known what he was talking about (doesn't surprise me)

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    Member AKDoug's Avatar
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    Staying on top of product knowledge is a never ending battle. Even some of my guys don't know the difference, but I try and teach them the best I can.

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    Default Thanks for all the help

    This cabin is a walk in. I can sled in in the winter, and that's how I'm going to be bringing materials in. And, that's one reason I'm reluctant to use concrete. Using the 2x12 base, I can prefab. and they'll be pretty easy to handle.

    One thing I've decided is to move the cabin to a more level location, forgoing the more exotic "cabin on a hill" version.

    I think key is going to be cross-bracing so the foundation acts as one unit.

    Here's the potential building site out of homer. Looking out towards the back of Anchor. For Akhelose, it's actually Fritz Creek.
    Attached Images Attached Images

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    Any time you use piers or posts for a foundation, the fewer points of contact with the ground, the better. You can level a cabin that sits on four post very easily. If that same cabin has 8 posts you're in for a lot of work. When you stand a cabin above grade you've assured the ground below it will freeze deeper than normal since you've removed the typical snow cover from the area under the cabin. Expect some jacking. Prepare for it. If you use lots of posts expect the ones in the center to jack the most. That's usually how it works out.

  11. #11

    Default 8x8 posts or railroad ties

    I have built a few cabins over the years useing 8x8 green treated posts as well as railroad ties. The key is that when you set them dig deep enough to get into gravel or gravel sand mix. I also wrap my post about 6 inches below and above the top of the ground with thick visqueen it acts alot like a sono tube and lets the ground slide when the frost comes. Dont wrap the whole post or it will hold moisture and rot. I have a 24x36 cabin on 18 posts it hasnt heaved ever. The ground moves as much as 6-12 inches from frost but my cabin is still plumb and square. Also when you refill the post holes dont let any organics or the over burden in or touch the posts. Fill with clean gravel or sand. If you are near a river or creek you can haul your fill from there. Hope this helps.

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