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Weekend Hillbilly
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# Posted: 23 Jun 2013 01:20pm
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I am in the process of starting a 16' x 24' cabin build in a remote area of West Virginia. I am planning to use treated 6" x 6" and 4" x 6" post for the foundation. The bulding site is relatively flat and I was hoping to build the cabin approximatley 20" off ground level. When digging the post holes - I hit rock. I was only able to dig four holes to 24", five to less than 10" and the remainder of the holes between 10" and 20".
One person's advice is to use the dug holes as they are, pour concreate around the post, and the weight of the cabin will hold the cabin in place.
Any wisdom before I proceed will be appreciated.
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bldginsp
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# Posted: 23 Jun 2013 06:26pm
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What is your frost line? You want your footings to be deeper than the earth freezes to prevent heaving earth from moving the footings.
Unless, that is, the rock you hit is bedrock. Bedrock is the best of all foundations because it won't move at all. But if the rocks you hit are not bedrock, they themselves could move with frost heave, and if your footings are on the rocks they will move too.
Are you sure you want to set wood in concrete? Even if it is pressure treated, it will eventually rot and then you have a problem. I'd pour footings a good 8-10 inches above ground with post bases, and then start the wood.
But if you are making a pole barn that's a different story. If so, you will need to dig a lot deeper than 24"
Good luck!
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Martian
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# Posted: 23 Jun 2013 07:42pm
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If frost heave is not a concern, I'd take a bar and chisel a hole in the rock, and then pour a pad with a bracket embedded in the concrete for the post to sit on. With good cross bracing, nothing is going to move.
Tom
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Storogoth
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# Posted: 24 Jun 2013 02:05am
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I was lucky and only had to dig deep holes for 2 of my 12 footings. Most I was able to hit bedrock on the surface or at less than 12-18". I built some cheesy forms out of particle board, drilled 1/2" holes and epoxied rebar about 6-8" into the hole. Pic #1. Some were up to 15" long and I then made a heavy wire cage for support. I did add maybe 10% extra portland to the Quickcrete when mixing (advice from on old concrete guy I knew) and so far they have been great. Had 3 winters, high winds, lots of snow at 8000' and very happy with the results. I am with Bldginsp on just pouring a good footing and topping with a post base. Pic #2. I bolted a 4x6 on that and then sistered pressure treated 2x4 under the beams for peace of mind. My crawl space is almost 4' and will give me a place for water tanks and lots of storage.
Hopefully the rock that you hit is bedrock and not just a small boulder right were you don't need it. If is is big enough you might be OK. Good luck !!!
Footing box
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Footing in crawl space
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Weekend Hillbilly
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# Posted: 25 Jun 2013 12:31am
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The frost line in our area is approximately 18 inches. I am not sure if I am into bedrock. We had an experienced dozer operater clear the area and he told us then that we only had approximately 18" of dirt on top of a shelf of rock.
I have debated about using concrete around treated post. Local contractors have told me that the post will outlive me (I am in my mid-40s). My biggest issue with concrete pads is how remote this cabin is - I do not have access to water.
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soundandfurycabin
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# Posted: 25 Jun 2013 02:33am - Edited by: soundandfurycabin
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Give the rock a good whack with a sledge hammer. If the hammer bounces off with a pinging sound, it's bedrock. If it thuds it's a boulder.
For a one story cabin, pouring concrete footers right on bedrock might be fine. If you are building two full stories then you have to take into account whether your area is ever subject to high winds, in which case pinning the footings to the rock becomes critical.
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