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willywilly2020
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# Posted: 2 Jul 2020 12:47am
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Hi cabin forum friends,
I have poured/built the first part of my foundation! It is designed to support a 20x12 shed roof cabin with two sides of deck.
It’s currently set-up to have two 25’ long parallel rows of piers with 12’’ sonotubes/piers every 5’. The rows are 12’ apart. Each row of piers supports a 6’’x12’’ beam. Joists are 2x10s, 16’’ spacing. They span 12’, and cantilever out 4’ on one side. See the attached foundation sketch.
My question: is 12’ too far apart? Should I add a third beam halfway between the two beams??
Thank you all in advance for your advice! I just worry that I haven't built it out enough (got some advice from my dad on original design that might be suspect)
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deercula
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# Posted: 2 Jul 2020 05:30am
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I am NOT a carpenter. Amish built my 16 X 30 with 3 rows of piers. 2 X 8 floor joist on 16 inch centers. Floor is rock solid. 4 years old in S.W. NY, fairly harsh winters. I was cautioned about using 3 rows of piers. Theory is that you will/could get a hump or a ditch in the middle if the piers move. If the piers move with 2 rows the floor will not be level, but it will still be a flat plane. Not sure if this is true, just how it was explained to me.
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Brettny
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# Posted: 2 Jul 2020 07:01am
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Didnt you alreaty ask this question in the other thread you had?
Is the roof canalevering out or the floor joists? 4ft is a huge over hang for either.
At a 12' front wall and 8' back wall and 4ft of over hang you may be covering the top of the windows with your over hang of you understand what I'm saying.
If you get a hump in the middle of your sono tube foundation you didnt go below the frost line. Usualy the ground freezes less under a cabin due to less moisture in the ground. I can kind of understand how you would get humps with a skid or block foundation because it shifts with frost. Shouldn't happen with sono tubes.
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Princelake
Member
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# Posted: 2 Jul 2020 07:08am
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I'd go online find a span calculator. 2x8 might be a bit bouncy. Worst case upgrade to 2x10 they are only a few bucks more per board.
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jsahara24
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# Posted: 2 Jul 2020 09:33am
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Quoting: willywilly2020 They span 12’, and cantilever out 4’ on one side. See the attached foundation sketch. My question: is 12’ too far apart? Should I add a third beam halfway between the two beams??
A 4' cantilever sounds like too much to me....
A 12' span sounds fine for 2x10s, 5' spacing for piers sounds good as well. Of course it all depends on your soil and the weight bearing on them....and i'm assuming you are below the front line....So without having enough information to really say, I would guess you should be OK.
but you might want to add some piers to catch your 4' cantilever...
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woodspirit
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# Posted: 13 Aug 2020 07:23pm
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deercula
Hey I'm in SW NY also.
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Aklogcabin
Member
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# Posted: 14 Aug 2020 10:01am
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Is the 4 foot cant for a deck ? If so you may feel the floor shake inside when someone uses it. May need some support there but you should be able to do later if needed. The rest looks good to me. Have fun n stay safe
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