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jessafiddle
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# Posted: 21 Jan 2013 08:44pm
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Hey everybody,
Hope you and yours are doing well.
I am starting my foundation Feb 1st, The cabin is being built in central
Alabama, I am using post and pier type foundation, cabin is 20x20 2 story. should I use 4x4 4 ft apart or 8x8 5 ft apart, the holes are already dug 4 ft apart 3 ft deep and I planed on putting crushed rock in the bottom, tamping, then setting the post on top of the rock and filling in with concrete, you will not hurt my feelings, In previous builds I have used poured footings, but budget is limited in this build. what you think, go ahead with 4x4 4 ft apart or even 8x8 on the corners?
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MJW
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# Posted: 21 Jan 2013 09:02pm
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We will be putting ours in the ground on or about Feb 8th and will be building our 20 x 32 using foundation grade 6 x 6s.
The foundation grade 6 x 6 seems to be the most often recommended post for the job.
Congrats on the start of your build. We are very excited about ours. 
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Just
Member
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# Posted: 21 Jan 2013 09:09pm
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In the north we would put, 8 in. of dry concrete mix in the bottom of the hole ,tamp it flat, put in the 4x4's ,and back fill with earth .but,,, i gess you have little or no frost so i'm not sure ??? You will need some cross bracing on your 4x4,s no matter what ..
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MtnDon
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# Posted: 21 Jan 2013 09:37pm
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My 2 cents... The foundation, whatever type, is the most difficult and time consuming thing to repair or improve, after all it's under everything else. If money is tight I believe you should try to skimp or delay on some other portion. Don't finish the interior walls or use the OSB sub floor as is for a year or two before doing it up nicer. It is my plain, bluntly spoken, opinion that putting piers in the ground on anything less than a rebar reinforced poured in place, concrete footer (16x16x8) is foolish, asking for future headaches.
If you don't want to do that then don't bother with the gravel. The plain dirt bottom, as dug, is no worse and no better and less trouble. Ditto concrete placed around the piers; waste of time. Pack the dirt back into the holes a few inches at a time. Hill it up around each post to coax water to run away.
Don't use 4x4 for a habitable building; go 6x6 or larger. The larger the pier the better it resists lateral movement in the dirt.
Seek out foundation grade post timbers and place an uncut end down in the hole on the concrete footer.
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jessafiddle
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# Posted: 22 Jan 2013 08:56pm - Edited by: jessafiddle
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8x8 it is, is there a reason for not filling hole around piers with concrete, it for some reason makes me feel better to put in concrete, can I just put a 2x4 concrete block at the bottom of the hole and back fill with dirt around the pier, it would save me from hauling in water.
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MtnDon
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# Posted: 22 Jan 2013 09:36pm
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My friend the structural engineer tells me it is a bad idea, I listen to him.
Quoting: jessafiddle a 2x4 concrete block at the bottom
Not sure just what kind of block you mean, but I've never seen a precast block with rebar in it. Rebar lends much strength to the concrete.
Concrete shrinks slightly as it cures. That makes for slight loose fit right off the bat.
Wood shrinks as it dries and expands when it gets more wet. The PT stuff we have here usually is much wetter than is normal when I buy it and want to use it. Put that in a hole with concrete around it and the posts shrinks and loosens.
If the wood is dry and then gets wet it expands. It might crack the concrete.
The only good thing about concrete around a post is it increases the effective surface area of the pier giving better lateral resistance. However it also can trap moisture in the wood and that is not good, even for PT.
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oldgringo
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# Posted: 23 Jan 2013 06:14am
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What is "foundation grade?" This is a term I've never encountered. Just PT, or is there more to it?
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tcmatt
Member
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# Posted: 23 Jan 2013 08:29am
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There are different grade of PT. Look for the numbers 0.20, 0.40, 0.60. The higher the number the preservative in the wood and the more suitable for harsher conditions. Some PT wood is suitable for above ground contact, below ground contact, structural below ground contact, etc. I've even seen it rated for immersion in fresh water.
For what its worth, I used 0.60 6x6's spaced 8' apart. I'm in very coarse sand (wooded dune).
hope this helps
matt
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Just
Member
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# Posted: 23 Jan 2013 09:53am
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home depot has fiberglass reinforst concrete mix just pore it in the hole and tamp ,,no water needed , it will attract water from the surrounding soil . IMO . WE HAVE BUILT MANY BUILDINGS THAT WAY, NEVER HAD ONE FAIL .LIFE IS ABOUT CHOISES .
JUST saying
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MtnDon
Member
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# Posted: 23 Jan 2013 10:16am
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= foundation grade if there is no heart wood
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MtnDon
Member
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# Posted: 23 Jan 2013 10:40am
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Quoting: Just it will attract water from the surrounding soil
Yes it will and many folks do that and anyone can do whatever they want. How many have dug it up after a time to see how strong it is.
Concrete needs the right amount of water to cure properly. If it doesn't get enough it can not cure to full strength. If there is enough moisture to start the process but not enough moisture to allow the cure to continue uninterrupted, the concrete will be crap. Dumping a pail of water in the hole is also bad practice and makes for lousy concrete.
The place fibermesh concrete shines is in resistance to surface cracking. Great for walks, driveways and floors. It is harder to work though. Foundations still use steel.
And yes, life is about choices; some good, some bad, or at least less good.
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Scott_T
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# Posted: 24 Jan 2013 11:12am
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What about using marine grade treated timbers like are used for beach homes along the coast? They are in contact with water at all times. Life expectancy? I would hope at least 50 years or there will be a lot of unhappy beach home owners if less than that.
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MtnDon
Member
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# Posted: 24 Jan 2013 01:06pm
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Quoting: Scott_T marine grade treated timbers
From foundation grade up there is a freshwater PT grade and a salt water PT grade. Either would be super, maybe more than needed to stick in the ground in most places. The major difference between the coastal system, is that those are driven deep into the sand. There is no footer just the pile. (name goes from being a pier or post to being a pile). The engineer calculates how deep they should be to develop enough friction between pile and soil/sand, to support the design load. You still need footings for our typical uses.
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Attreadwell
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# Posted: 29 Jan 2013 03:57pm
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I'm going the same route. Post on poured concrete footers.16x16x8 with rebar at 4" line. If I use marine grade pt 6x6, how long will they last? Is it worth the money over .60 pt 6x6?
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