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40ACRZ
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# Posted: 4 Jun 2024 11:39pm
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Trying to determine a somewhat economical design for a pier and beam cabin to be built in central Texas for a hunting cabin. Thinking an 18’x36’ footprint on a very minimally sloped site but can’t determine what design to use for the piers. Concrete filled tubes may get too expensive. What would my alternatives be? 8”x8” pressure treated wood? Concrete blocks? Other?
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travellerw
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# Posted: 5 Jun 2024 01:17am
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My cabin is 16X28, 2 stories and it was built 4 years ago.
Its built on a 2ft hole, filled 3/4 with packed road crush then a precast slab. On top of that is cinder blocks(2 side by side). I then used pieces of pressure treat (2x6) on top to shim up each beam to level (there is at least 1 piece of 2x6 on top of each cinder block to ensure the beams don't touch concrete). Pieces of floor tile can be used if you need thinner shims.
I have 2 main beams and 5 of these supports for each beam. A cabin the size you are suggesting will require 3 beams with 6 supports each. You may want to rethink the 18ft width as I don't know anywhere to buy 18ft dimensional lumber. So you would need to cut 2ft off (waste). Also at 18ft you are beyond the span for standard lumber and will need to buy floor joist grade or go with engineered stuff.
Now with all that said, if I did it over again I would probably just go with a screw pile. I found a company that will do screw piles for $300 per pile driven with a welded pile cap. It would have saved me a HUGE amount of work and gave me a foundation resistant to frost heaving.
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Brettny
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# Posted: 5 Jun 2024 09:54am
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The foundation is not the place to cheap out on.
Sono tube placement should be done under every joint in a girder. With 36' you can do 9' spacing with 18' lumber or 6' spacing with 12' lumber. You would be looking at 15 or 21 sono tubes with a center girder. I would also pull the outside girders in 12in and the outside sono tube in from the girder ends 12in.
I would get 18' floor joists.
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40ACRZ
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# Posted: 5 Jun 2024 11:54am - Edited by: 40ACRZ
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Quoting: Brettny Sono tube placement should be done under every joint in a girder. With 36' you can do 9' spacing with 18' lumber or 6' spacing with 12' lumber. You would be looking at 15 or 21 sono tubes with a center girder. I would also pull the outside girders in 12in and the outside sono tube in from the girder ends 12in.
We were already thinking 15 piers (3 rows every 9’). But I don’t understand your last sentence about pulling the sono tubes in 12in.
What diameter sono tubes would you suggest if I go with 15 piers? 10”?
I’m not yet sure how deep I can dig for the tubes but what would be an optimal depth. Decent chance I’m going to hit large rocks 1-2’ under the top soil.
What size wooden beams would you suggest? And what size floor joists?
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travellerw
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# Posted: 5 Jun 2024 03:45pm
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Quoting: 40ACRZ What size wooden beams would you suggest? And what size floor joists?
You need to do some googling about spans and beams for buildings. Especially if you plan to use hardware store materials (SPF wood). This part takes some engineering and different counties may have different rules for code. The foundation and the "dance floor" are areas that you don't want to screw up.
P.S. The numbers also change if you want to use pressure treated material.
While we can provide you with some general advice, you really need to do the numbers yourself to be sure. Its your money and I wouldn't trust it to advice from a bunch of internet strangers.
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Aklogcabin
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# Posted: 5 Jun 2024 04:06pm
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We used used cedar utility poles I got from a company that does power line installation. Works great. Inexpensive and will never rot. After installing, I cut them level and added a shoulder cut into the top to bolt 6x12 beams with galvanized bolts.
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Brettny
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# Posted: 5 Jun 2024 07:51pm
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Quoting: 40ACRZ We were already thinking 15 piers (3 rows every 9’). But I don’t understand your last sentence about pulling the sono tubes in 12in
Pull the sono tubes in from the end of the girders so there well under the building.
12in tubes for anything structural.
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spencerin
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# Posted: 7 Jun 2024 02:55am
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#1 Sonotubes
#2 Foundation-grade 8 x 8s or 6 x 6s with sleeves
#3 Block, but I would avoid this for a cabin your size
9' spans between piers is too far apart. Like previously mentioned, consult span tables. But, most people would recommend 4' to 6' between piers.
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Brettny
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# Posted: 7 Jun 2024 10:03am
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Here is how we layed out the piers for our 20x32, isqft smaller than a 18x36. The square around the piers is the outside of the building. We used 2x10x20' floor joists and trippled up 2x12x16 and 2x12x8'' for the girders. Every break in the girder boards is over a pier.
You can buy 2x10 and 2x12 lumber longer than 16' at most any lumber yard up to about 24'. The cost difference is prety minimal but makes putting your floor joists on really easy.
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