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mkphillips4
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# Posted: 1 Dec 2014 13:06
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New to forum. Plan to begin construction on a cabin in 2015 with the end goal of getting it under roof by fall. Looking for recommendations on good reference material. Cabin will be completely off-grid. Biggest hurdle right now is understanding how to properly construct a pier and beam foundation. Web search isn't helping much.
Thank you in advance.
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bldginsp
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# Posted: 1 Dec 2014 13:42 - Edited by: bldginsp
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Welcome to the forum.
To 'properly construct a pier and beam foundation' you would need to hire an engineer. Just because, to properly do it, calculations need to be done and existing soil conditions and freeze depth need to be considered.
But, for most small cabins, people don't hire an engineer, they sort of wing it. Most important things are to get below your frost depth to avoid heave and, if you have a snow load, be sure your piers have enough area to support the load.
If you draw a plan or give us a basic description of what you plan, I'm sure several people will weigh in with suggestions. But I doubt you'll find a how-to book that will explain how to do it because the writer of the book cannot take all factors into consideration for all the different design possibilities. That's what engineers do.
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mkphillips4
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# Posted: 1 Dec 2014 13:55
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Great feedback bldginsp. Cabin will be 24' x 28' with a 6' porch spanning the entire 28' length. Wanting an 8/12 pitch over the main structure sitting on 8' walls which will allow me to add a loft/storage area. Porch roof will tie in with a 4/12 pitch. Plan on using sonotubes but the spacing and distance between each has me quite puzzled.
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MtnDon
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# Posted: 1 Dec 2014 14:29 - Edited by: MtnDon
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For something of that size I do not recommend using piers at all. IF you need to build something that size on piers I would look at the Bigfoot system. They still can not meet existing building code criteria, but they do have some impressive enough test data for lateral resistance to movement.
Compare the costs of digging the required footing holes and cost of materials to the cost of digging out for a full perimeter concrete block (or poured) wall and footing.
What is your climate zone? If the frost depth is shallow as in much of the south and SW all you need for a full perimeter footing is a 12 inch deep trench. You can dig that with a rototiller and a shovel.
Tell us more about where you are, frost depth, terrain, snow, rain, wind, and so on.
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mkphillips4
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# Posted: 1 Dec 2014 18:08
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interesting MtnDon. Didn't think the Bigfoot system would have that great of an impact. I assume it provides increased stability for lateral loading. I will investigate the use of block foundation. Frost depth in Kentucky is 24". Anyone know how the costs stand up when comparing Pier system to block foundation?
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Don_P
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# Posted: 1 Dec 2014 21:23
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IIRC the test data for bigfoot revolved around one of their larger sizes, a very short out of ground height and their idea of failure and what most folks would consider a failure were two different things, read the footnotes. Although they advertise that they are code approved, they are code approved if designed by an engineer.
Lateral stability is the big problem with piers and the reason why they are not prescriptive in the codebook, and why the design info that used to be available has been retracted. Most important things are to get below frost depth, be footed well enough not to sink AND be laterally braced (just as everything sitting on your foundation is required to be). Not only can they move up and down, piers can overturn relatively easily if not well braced by something.
With pier and beam vs perimeter foundation, some hidden costs;
The cost of the girders is one thing to factor, also floor vibration and deflection are not only caused by the joists, any girders in the mix are also deflecting and adding to floor bounciness.
You need to do a better job insulating and protecting the insulation.
You need to protect plumbing and utilities between ground and the floor.
If piers were a real bargain contractors would be all over them... you don't see that.
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mkphillips4
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# Posted: 2 Dec 2014 12:30
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Don_P, I appreciate your thought process. I will investigate the use of a block foundation. No larger than the cabin will be I don't see it blowing up my budget. At a 24" frost line I would venture that 3 courses would bring me to just above ground level. The main issue will be getting the materials to the job site. Property location is a 1.5 miles off a small country road down an old logging road with a couple of interesting grades. It sounds like the conversation is worthwhile though.
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Don_P
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# Posted: 2 Dec 2014 21:22
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Seems like the vast majority of the houses I've built were down that road. I was in my 20's when we followed a lost cow to the top of the hill and decided it was a good place to put a house. The block truck left the blocks at the bottom and we shuttled them up in the back of the old Willy's. Pouring required a dozer to pull the trucks up, but it all worked out. The dozer built a road back to the cliff/ rock pile at the far end of the property while he was waiting between pulls.
The footing is typically 8" thick and the bottom of it is at 24" below grade, so 16" or 2 courses to grade if the site is dead level. Remember that untreated wood needs to be a minimum of 8" above grade and no untreated girder framing closer than a foot to grade or untreated joists closer than 18". Probably more like 5 courses.
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