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sroyj
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# Posted: 17 Jan 2012 11:40
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I've spent some time over the last couple month checking out this site and as the time to start my cabin grows near I could use some advice on a foundation. My plan is for a 12x24 cabin on a lot in northern Maine. My first thought when I started thinking about this was that I could just put my cabin on blocks (over gravel). The more I read and spoke with people the more it seemed like this was a bad idea. But, as I look for the "right" way to do it, I go from a simple, inexpensive, DIY solution to one that could require renting some excavating equipment (my understanding is the frost line is about 80" down, require a lot of concrete (where I have no power or water), could mean hiring a contractor, and pushing the cost of this project way up. So, as I continue to mull this over I periodically go back to the original plan of blocks and wonder is it really so bad? The ground is very solid. I believe it is compacted gravel from some past logging operation. I know I could still see frost heaves that could move things around a bit, but how badly, and how big of a problem would that be? Is the worst case that I would need to re-level it from time to time? I do hear people say blocks are OK for a "small" cabin. What is "small"? Another option I've seen is Diamond Piers (Pin Piers). Is anyone familiar with those and would they make sense for my project? Any input would be greatly appreciated.
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fpw
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# Posted: 17 Jan 2012 11:58 - Edited by: fpw
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It is always better to get below the frost line. 80" is not right for a frost line in Maine, I would recheck it, your frostline will be less than 40-42" (which is the MN frostline - climate a bit more extreme).
Piers and stumps work fine, lot of digging with a post hole digger and you have to haul in sack-crete. It took me two full weekends to dig and fill fifteen 20 inch diameter holes that were 42" deep.
If you build it on grade, it will get wonky with time. You can give yourself some adjustment by intstalling large screw jacks. Folks use this type of thing up in Alaska to combat the thermafrost.
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sroyj
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# Posted: 17 Jan 2012 13:39
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Thanks for the reply fpw. I'm unsure on the depth of the frost line. I saw a map that said 80" and just read a post that said 6'+ so it does seem like it's pretty deep. I should try and call the town manager and see if he can make any suggestions or point me to other cabin owners or contractors that can provide some suggestions. What I'd really love is a full walkout basement to store dirt bikes, snow mobiles, etc., but I'm afraid to even ask what that will cost. ;-) I guess I really need to make time to make some phone calls.
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MtnDon
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# Posted: 17 Jan 2012 14:34
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I seriously doubt the 80" frost depth. Frost Depth Map
Maybe 80" of snow ???
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sroyj
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# Posted: 17 Jan 2012 15:51
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Thanks for the map! That puts me closer to 55". Still pretty deep, but better an 80! If I use 2x8s for the floor, is there any rule-of-thumb for how many piers to use on a 12x24 cabin?
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MtnDon
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# Posted: 17 Jan 2012 18:01
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Depends on the size of the main support beams (girders) and the span between piers, the expected snow load, load bearing capacity of the soil and if it's one story, has a loft or is a two story.
50 psf snow, one story, two 2x8 make a girder if spaced at 4'10"
70 psf snow, one story, two 2x8 per girder at 4'6"
or
50 psf snow, one story, three 2x10 per girder at 7'5"
70 psf snow, one story, three 2x10 per girder at 6'10"
If the loft only had a mattress, no large items stored up there the above sizes would be pretty good too.
So the next question is what is the expected, average, ground snow load in psf? Parts of Maine get into the 80 to 100 psf range. That goes beyond the charts for a rough guide would be to cut 6 inches from the spans above for every extra 20 psf snow.
I'd use nothing smaller than 6x6 for the piers.
When it comes to sizing rafters they will also need to take into account the high snow loads that most of Maine gets. And because of the heavy snows if you were thinking of a loft I would not recommend dropping the loft joists down the wall studs at all.
Note: A 12 foot span (floor joist) is getting to be about the maximum for the average #2 lumber sold in most places. That's with 16" centers and L/360 as maximum deflection.
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MtnDon
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# Posted: 17 Jan 2012 18:07 - Edited by: MtnDon
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NE snow map
Note that areas marked "CS" are rated on a Case Study basis. There could be areas that are very high, 120 psf+ or lower. This common in mountainous regions. Then checking with local building departments is advised.
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sroyj
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# Posted: 18 Jan 2012 13:27
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Thanks for the great information. Thinking about snow does have me rethinking the roof a little. Mostly to go from 2x6 to 2x8. I'm going with a steep pitch (about 45 degrees, and with metal so it should shed the snow well, but I think it would be worth going up to the 2x8s to be safe. Make sense? As to the foundation, I'll need to try and contact people up there and see what my options are. It's hard to research from Massachusetts. It seems like very few businesses are online, so finding them and getting information is going to take a bunch of phone calls I think.
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optimistic
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# Posted: 24 Mar 2012 19:44
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HI
I'm by no means an experienced builder when it comes to foundation but I did research for my own future build and I found that what will be the easiest and reliable solution is cement piers. You can rent a two or one person auger at home depot - it runs on a gas motor so you don't need electricity - they dig holes quickly for you. Then you can buy at HD as well those tube forms (they have info online on how big you need per load) and another time saving thing will be those big foot system for the footer which takes two minutes to connect to the concrete tube.
You go out there with someone and the two man auger, dig down under the frost line, fill with gravel, connect form tubes to big foot (you need to screw it to each other and cut with a utility knife - all easy and not requiring electricity), place it down in the holes and align and plumb them, back fill it, insert some rebars and a metal connecter to the type of foundation you will have over it (6x6, triple 2x10, and so on), and then you need to fill it with cement. That is where you need to decide if you are going to mix yourself or try to get a cement truck to come there and pour it for you.
Bigfoot website has a calculator in which you put the amount of piers, their diameter, height, and the big foot system you will use (they come in different sizes) - and it will tell you how many cubic yards and bags you need... Mine was like 90 80lbs bags for 8 10" piers so I will try to get a cement truck over there. No way am I going to mix so much cement on my own. Worst worst case, if no cement truck will be willing to come, I will try to rent a commercial size mixer (the one in HD is for like 3-4 bags) so I can mix a lot of cement and fast.
Good luck!
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MtnDon
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# Posted: 24 Mar 2012 20:12
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MMmmm.. Bigfoot footers do work, but the smallest requires a 22" diameter hole at the bottom end, IIRC. The auger at my HD will only do an 18" diameter hole up to 4 foot 2 or 3 inches deep.
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optimistic
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# Posted: 24 Mar 2012 20:20
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Yup - it will do 18" wide and 51" deep. But you can just drill two right next to each other (or even three) and then clear it with shovels. look how fast it goes - http://www.youtube.com/watch?v=QuJKPZQetZo
Even if you have harder soil then that it will take a few minutes to drill two-three holes right next to each other.
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jgiffi
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# Posted: 24 Mar 2012 23:49
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Check your site first because in my area there were alot of rocks and we couldn't get the 2 man auger to get more than 12 inches deep. Found out later that everyone in the area uses excavators to dig the holes. If you hit even a small to mid size rock with that thing it won't have the power to push around it.
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