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toofewweekends
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# Posted: 9 Jun 2024 03:57
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I'll be building a 16x16 cabin in Alaska, 120m north of Anchorage. The current cabin sits on nine 6x6 PT posts, all of which were wrapped in thick (6 mill?) black plastic on the theory that frost movement will slide on the plastic and not jack the foundation. The current 16x20 cabin has stayed very level for 20 years, so part of me says go with success. The other part thinks, if they are surrounded by good gravel why put a waterproof raincoat to hold any moisture next to the post. Opinions? Experience?
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Steve_S
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# Posted: 9 Jun 2024 14:24
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Well, things are not terribly stable in the North anymore as the permafrost is thawing & heaving everywhere, faster every year. Unless you're anchored to bedrock (and even then) you're going to run into issues. I feel that this is something to be carefully considered, moreso now than ever before.
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gcrank1
Member
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# Posted: 9 Jun 2024 16:55
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Is it really so bad in the north country to go with a 'floating foundation' for smallish structures?
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travellerw
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# Posted: 10 Jun 2024 15:55 - Edited by: travellerw
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Quoting: gcrank1 Is it really so bad in the north country to go with a 'floating foundation' for smallish structures?
We just did winter 3 on ours (which is completely floating). There has been some movement for sure, however pretty minor. I have one drywall crack where 2 sheets butted (should have used mesh tape instead of paper). We have seen temps of -40C numerous times.
Now with that said, the cabin is on a slight hill with very well drained soil. My opinion is the building site is key for a floating foundation. It must be high and dry.
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ICC
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# Posted: 10 Jun 2024 19:16 - Edited by: ICC
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Foundations in Alaska are a special case. Much of what we 'southerners' know is wrong, maybe even really bad ideas. I would seek advice from local engineers.
I read once that 85% of the land surface in Alaska is sited above permafrost. I also read someplace that slabs should have 3" (R15) minimum of foam under them with more being better. Almost half of the Alaska pipeline is elevated, because the heat from the oil would likely cause problems with permafrost melting. So it's elevated, insulated.
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paulz
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# Posted: 10 Jun 2024 19:42
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Pretty sure Dick Proenneke’s cabin was floating. Lasted his lifetime, and still there afaik.
Now there is an Excellent watch if you can find it (Alone In The Wilderness).
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Brettny
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# Posted: 11 Jun 2024 00:01
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To me any building I dont want to have to put a new foundation under in my lifetime means no wood in the ground. Yes you could buy really really good pressure treated post but I bet they cost more than screw piles or concrete sono tubes.
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toyota_mdt_tech
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# Posted: 11 Jun 2024 01:03
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Quoting: paulz Now there is an Excellent watch if you can find it
I own the DVD, in fact, its at my cabin now as part of my DVD library.  
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travellerw
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# Posted: 11 Jun 2024 02:52
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Quoting: Brettny Yes you could buy really really good pressure treated post but I bet they cost more than screw piles or concrete sono tubes.
I think it depends on location. I couldn't find anyone to do screw piles when I was building. Then I found a company that does them for $300 per (driven), but it was too late. Even then I did "floating" so I could claim a mobile building and have more relaxed codes.
Concrete is pretty expensive these days and deep piles in northern climes can use a ton. Plus the rental equipment (mixer, concrete vibrator, ect). All expensive.
However, you can't put a price on doing things the correct way and passing it down to your kids. This topic seems to come up pretty often and there are lots of opinions. Location is such a big factor that I'm not sure we can give any meaningful answer.
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Brettny
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# Posted: 11 Jun 2024 12:22
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A 1'x4' sono tube with the concrete to fill it is $50. That's not that expensive..compared to blocks you could consider is expensive but there different types of foundations.
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paulz
Member
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# Posted: 11 Jun 2024 21:20
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Quoting: toyota_mdt_tech I own the DVD, in fact, its at my cabin now as part of my DVD library.
Yeah I watched nightly when building my place. Talented, hard working man. Here’s a free half hour of his journey. If you haven’t seen the whole two part doc, pony up, you won’t regret it.
https://www.google.com/search?q=dick+proemneke&ie=UTF-8&oe=UTF-8&hl=en-us&client=safa ri#fpstate=ive&vld=cid:87c17024,vid:hy-4NxJRxNQ,st:0
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travellerw
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# Posted: 12 Jun 2024 02:26
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Quoting: Brettny A 1'x4' sono tube with the concrete to fill it is $50. That's not that expensive..compared to blocks you could consider is expensive but there different types of foundations.
That sounds about right. So up here we need to go 10ft deep as the frost line is about 8.5. Factor the costs of the tube, concrete, metal hardware, rentals and you are darn close to the price of a driven screw pile. Then factor all the work.
For our foundation I used precast square flat pads at $12 per, plus 2 "reclaimed" cinder blocks at $6 per. So, $24 plus the cost of the road crush (generously another $20). Lets just say 50 per support footing. Pretty cheap, but a floating foundation and you will need to deal with building movement for sure (at least in frost areas).
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Brettny
Member
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# Posted: 12 Jun 2024 14:10
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10' deep frost line..I would also do a floating foundation. Generaly 4' will cover about 95% of the lower 48.
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travellerw
Member
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# Posted: 13 Jun 2024 03:57
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Quoting: Brettny 10' deep frost line..I would also do a floating foundation. Generaly 4' will cover about 95% of the lower 48.
Its cold AF here.. but I feel for the guys in Alaska. At least we don't deal with permafrost here..
Sigh, I'm planning my septic tank and all the experts are saying the bottom needs to be at least 9ft (preferably 10ft) due to our "casual use". Thats a pretty deep hole!
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gcrank1
Member
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# Posted: 13 Jun 2024 13:59
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Curious....what dif does casual use make?
Reg use is how deep?
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Tim_Ohio
Member
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# Posted: 13 Jun 2024 14:56
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Why not build it on runners, like a sled? If built well, the entire structure will float as the earth moves. Of course, you will have factor in movement for utilities, like water line, sewer and electrical feeds. However, the foundation under could be a nice bed of heavy gravel. It would cost a lot less. I dunno, there has to be a way where you don't have to go so deep with footers.
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gcrank1
Member
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# Posted: 13 Jun 2024 15:36
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Especially, imo, for a smallish structure.
But I don't live in Alaska 
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Brettny
Member
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# Posted: 13 Jun 2024 15:47
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Quoting: gcrank1 Curious....what dif does casual use make? Reg use is how deep
If a septic tank isnt deep enough and your not inputting warmth it can freeze.
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travellerw
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# Posted: 13 Jun 2024 15:48
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Quoting: gcrank1 Curious....what dif does casual use make? Reg use is how deep?
Regular use "introduces" new fresh bacteria and bacterial "food" often (probably daily). As the bacterial breaks down the "food" they generate heat. That keeps the tank from freezing even if its above the frost line.
Since we will only use the cabin 5-6 weekends over the winter we don't introduce enough "stuff". The bottom of the tank must be below the frost line or it will freeze once the bacteria run out of "food".
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gcrank1
Member
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# Posted: 13 Jun 2024 18:11
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Im feeling better about our composting T all the time.
Yeah, it doesn't 'work' in freezing weather either, but for a few winter visits it has been fine the past two years. All goes into the hopper at visit end and come spring it activates on its own again.
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