Good morning,
New to the forum, Ive been searching and reading a ton of older build posts that are similar to the build I'm starting. I have some questions, my hope is they are not super redundant and I've just not used the search option enough.

Unusual spring winter storm here so I figured I would ask some questions.

I am starting to build a 32x20 cabin it will be two stories on a mountain ridgeline. I just completed digging the footing holes. I will be doing sonotubes on footings. There are no building codes in my area I need to follow but I will spend the money to "over build" with some constraints. It has been almost impossible to get contractors to show up so that is why I have decided on a pier foundation.

The soil is rocky, shale, and clay. I have excavated 18 pier/footer holes, (3 rows of six). I plan on pouring 2'x2'x1.5' footings, they will be 24-30" below grade. I will be using 12'" sonotubes formed up so I can pour the footer and pier together using pump truck. I will be adding rebar to the footing and sonotubes. 

I'm pretty green at all of this but the folks Ive met and discussed with think I'm over doing it, (I'm fine with that). Also the walls will be 2x6, 10 foot main level with approximately 4.5 foot knee wall and a 10:12 roof pitch. The upper level loft will be approximately half the lower level so 32x12 or so.

I'd really appreciate and insight or suggestions on how this all sounds. I've done a lot of construction in my day but that is definitely not my profession. I'm from another state with flat land so this mountain building is foreign to me.
Thank you in advance for any help you can offer.

That's going to be a very busy day when the ready mix truck arrives.  I would not be so brave to try this plan, it will be heartbreaking if the concrete poured into the Sonotubes merely flows down and becomes part of the wet footing.  The "slump" of the ready-mix has to be rather exact for this method to work.

I would suggest you pour the footings first and then, after some cure time, the piers.  Use the re-bar to tie the footing to the pier.  Two separate ready-mix deliveries, separated by some time, would work.

I would study the possibility of mixing the concrete for the piers using a on-site mixer.  This would give you more control of the process, and you might be able to reuse one (re-engineered) Sonotube for all piers.  Those Sonotubes can get pricey. 

JRR
Thank you for the input, your concerns were my concerns exactly. I believe the Perkins builder brothers did a video with Crafted workshop where they used a 3 slump, (where I got the idea).
I don't have power at the site for a mixer or water, ( I do have a generator and a 60 gallon water bladder though). The pump truck will cost me $800-$1000. The piers will only be at most 75 bags of concrete. I think I will take you advice and err on the safe side.
Unless a number of folks that have tried this monolithic pier/footer pour and it worked? I have my doubts as not much info pops up on Google.
Thanks again JRR!

Thoughts on my footing size for the two story? I can bump it up to 2'x2'x2'

Best,

Mike

I'm not a fan, and have no experience with pier foundations.  But I realize piers have their place and value in certain situations.

I tend to wonder about individual pier footings.  I would be more inclined to have three continuous footings with rebar turn-ups at each pier location.  This would, of course, cost more material .. but I would be more comfortable about stability.  Of course, every thing begins with knowledge of your property and the nature of your soil.

I use to use a slump cone and actually measure "slumps".  Every thing else being equal: the lower the slump, the stronger the concrete.  

BUT .. 3" slump is not very workable, and can tire muscles pretty soon if there is much manual placement required.  Its great for a massive monolithic pour.  I prefer 6" for my smaller DIY projects.  But as more water is added, more Portland cement should be added to the mix to keep the strength up. Talk to your concrete supplier about your plans.  They may suggest additives, such as retarders.   

I have used a pump truck but also hired a sub-contractor familiar with pumps .. .. because I was out of my depth.  I'm OK with a regular ready mix truck with pour-chutes, but no pumps please .. unless required.

A continuous footing is vastly superior to individual footings under each pier.  The continuous footing "ties" the foundation together, resisting any lateral movement from the bearing soils while providing support for individual piers distributed over a larger area compared with spot footings. Masonry (CMU) piers can be installed and tied to the continuous footing with rebar and filled voids in the CMU. Or a concrete pier can be poured in a form onto top of the continuous footing.

The plan is to go as deep or deeper than the historic frost depth?

.... do a search on elevated or raised foundation design. Southern Pine Assoc used to have info available on using a continuous footing and various types of pier-like supports for a wood floor assembly.