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225digger
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# Posted: 9 Mar 2012 08:20pm
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hey everyone , so much on this site i might have passed the info , or just forgot what i was reading lol .
but anyways , this summer is the summer for my cabin build , its not going to be to small . 20x26 roughly , i guess its boarder line small house , but , the foundation , this is going to be built in north west wyoming , the ground is mainly sandy with limetone base , so it wont be to bad to dig holes for a pier type foundation .
but my question is this , between a pier foundation , and just using those concrete blocks that you can set a post onto . which one would you go with ?
obviously i know better to even ask this question but maybe there is something im over looking and should just keep it simple since its not going to be a permanant living cabin .
any insight on which foundation you would go with ?
thanks !
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225digger
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# Posted: 9 Mar 2012 08:46pm
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i should also mention , the pier style i am mentioning is not your typical concrete pier with wood attached to the top of it , im talking 6x6 post in the ground , with concrete poured into it , like a pole barn type building
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Just
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# Posted: 9 Mar 2012 10:31pm
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Quoting: 225digger n north west wyoming ,
I THINK YOU WOULD BE MUCH HAPPYER WITH A FOOTING BELOW THE FROST LINE .with a cabin that large.
dig your holes 4 ft deep pour in 6 in cement then x some rebar then 6 more in. cement ..tamp the cement flat.then stand a 6 x 6 or larger pt post on the cement and back fill with earth only NO CEMENT.or the post will heve from the frost.brace the standing pt posts against side forces.about 1 post every 50sq. ft. of cabin that size.
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MtnDon
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# Posted: 9 Mar 2012 11:16pm - Edited by: MtnDon
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Those "concrete blocks that you can set a post onto" are called deck blocks, not cabin blocks. And as far as that goes in any location with winter freezes like WY I would not even use them for a deck. 6x6 foundation grade PT piers, set below frost depth as a minimum, on rebar reinforced concrete footers. Nothing less for your small house. And plenty of lateral and lengthwise bracing from piers to beam and joists.
Deck blocks offer zero uplift resistance. And little if any lateral resistance.
Concrete belongs under the piers, not around them as 'Just' mentioned. Ram the dirt back in around the pier, hard packed.
Lower edges of beams/girders should be 12" above ground minimum or be made from PT lumber. Floor joists should have their lower edges 18" above ground or be PT lumber if less. On the other hand don't make the piers poke up any three feet unless you are ready to put 6-7 feet in the ground.
Have you any idea what the psi load bearing of the ground is? One story, loft - no loft, two story??? This all affects the foundation.
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jgiffi
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# Posted: 9 Mar 2012 11:31pm
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Don, great break down of the options and what to look for! When my building inspector came out in my area he said if you are above 2ft from the ground I had to cross brace the 6x6 together and then back to the middle posts. PT 6x6 was a cost effective means of creating an appropriate foundation for the camp because poured concrete and block would have placed me well above budget and thought it would be alot more challenging leveling and placing the block. I placed the 6x6 closer together as well as used wider floor joists so that if I decided to add a second level at a later date I could do so without doing anything to the foundation.
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225digger
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# Posted: 10 Mar 2012 12:01am
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with the piers stuck in the ground and cement poured around them what is wrong with that ? there are plenty of pole barns built this way here in the north east {im in Pa around harrisburg}
i dont know what the load bearing of the ground is , but the cabin will be one story with an upper loft .
but for snow load , this is northwest wyoming , but it gets little snow , on average its 12" of participation a yr .....
one thing that helps , or does not help , no codes or building inspections , so im sort of free to do what ever , but i want to do it right , and having done a few commercial buildings with permits and such i know what is right or wrong , i guess im just looking for some insight to keep the budget low .
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MtnDon
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# Posted: 10 Mar 2012 12:29am - Edited by: MtnDon
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Quoting: 225digger ...with the piers stuck in the ground and cement poured around them what is wrong with that
Concrete poured around piers like that offers many surfaces for ice / frozen dirt to "latch onto" as the hole sides are seldom smooth and straight. That can exert sufficient up force to lift the post. Not saying it will happen for sure or that it will happen to every pier every year, but there is a very good chance it will happen sometime. Once a pier frost heaves, it does not go back down in spring. Some buildings do not exhibit problems if their windows and doors are loose fitting.
I have a gate post I set in concrete 20+ years ago. It has moved upwards about 5/8" over time. It doesn't move every winter, just on the colder ones it seems. I keep moving the latch. It serves as a reminder to me. The hinge side is anchored to the house; that does not move.
Plus it is a waste of concrete in many cases.
The only advantage to concrete around the pier is that increases the cross section area of the pier. That in turn increases the ability to resist lateral (horizontal) force. Piers won't necessarily move sideways; they are more prone to rotate around some point along its buried length. The top goes one direction and the bottom goes in the opposite direction. If you want to do that, set a large diameter (12" minimum) Sonotube full depth in the hole with the PT pier in the middle. Bring the concrete to above the surface and form to shed water away from the pier. My second closest neighbor in the Jemez did that using 20" dia. tubes, 4 feet deep.
The best piers are ones that are driven into the undisturbed earth. Not something an owner-builder can easily do.
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razmichael
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# Posted: 10 Mar 2012 09:26am
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Quoting: MtnDon set a large diameter (12" minimum) Sonotube full depth in the hole with the PT pier in the middle
This is exactly what I was about to ask about. I'll be building (hopefully this summer) in an area that includes a cold winter and about 3 ft of clay before you hit sandy soil. The cabin will be 16 by 24 with the front 8' being a deck with an overhang loft. Most of the cabin will be on fairly flat ground so I'll likely just dig down below frost and use sonotubes with cement (so the beams can rest directly on the cradles inserted into the top (maximum about 18" above ground). The front however will have a fairly big drop of about 3' so I was considering foundation grade posts as described in the quote. If I can get the posts long enough they can continue up to the loft support so I have no junctions or connections between the cement pad and the upper loft floor. Would it make sense to pour the base/pad, insert the sonotube, back fill around it and then add the post and pour cement? This might allow for some adjustment to make it easier to keep the post vertical. I would cross brace plus the posts would be connected to the floor beams and the upper level.
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MtnDon
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# Posted: 10 Mar 2012 10:53am
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Tall piers that are connected to upper floors, ceilings and roofs are good as long as all the connections are secure and use enough nails for the forces that will be acting on them. That's what makes a pole barn type of construction work. There are nailing schedules in the IRC.
When a wall is framed between two or more such posts and then skinned with plywood or OSB then the entire wall braces the structure. It's called a brace wall or if an engineer designs it for a particular application it is called a shear wall. Brace walls are covered in the IRC as well.
Links to the IRC are found in the resources and links board on this forum.
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