20 x 30 cabin on the Illinois River in Oklahoma

Started by Eclour87, May 05, 2016, 02:47:41 PM

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Hello everyone!
I've been lurking on here for a short bit, but finally decided to start a thread!  My wife and I recently purchased some land on the Illinois River in Oklahoma and will begin building cabin soon.  We're pretty excited to get started!  We've never built anything of this size before (ok, a playhouse on stilts for my daughter is the closest thing to a cabin that we've built, but that counts for something, right? 😁).   My wife's grandpa built his own primtive cabin many years ago and it's been our dream to build our own someday.  We were inspired by Nevada Mike's Alaska cabin to go with the 20x30 cabin plans with the loft.  We're still a little ways off from getting started, but my wife is documenting the build on instagram.  If anyone is interested in following along (it could get interesting and is likey to include a comedy of mishaps, but we will persevere!), the link is http://instagram.com/heavenandnowhere.  I'll definitely be posting here for advice along the way.  I've already have a list of questions after pouring over the cabin plans.  Anyway, just wanted to introduce myself and say hello to all!



Great! Remember, there is no such thing as too many pictures.


Look forward to following your build.  I went to graduate school in Fayetteville, AR and used to travel up to the Illinois River to hunt - great area!


Welcome very much Eclour87!

Where abouts in Oklahoma? Near West Silaom Springs, Tahlequah, Ten Killer Ferry lake?

How awesome it must be to have land on or right near a lake.
Click here to see our 20x30 and here to see our 14x24.


Ajbremer, we're close to Chewey, OK, which is about half an hour north of Tahlequah.  We're prettydarn excited about being close to the river!  Can't wait to get started on the cabin!  We'll definitely post many pics as we progress.


Thought I'd post a couple pics of the land and the river.  We negotiated some dozer work into the purchase price of the land, so we're pumped to already have a driveway and buildsite cleared.  Let's see if I followed the picture posting process correctly.

Walking the land after we bought it.

First time fishing the river.




That river runs through your land? If so that's fantastic. I can see a deck looking out over it. Jealous.


Great site, and love that you're taking your little one fishing!


Azgreg - Unfortunately, the river doesn't run through our land. We couldn't afford river front quite yet.  Maybe someday. 😁 That point is about half a mile from our land, but we have private acess to it.  We originally wanted to build on the river, but after the historic flood in December 2015 where the water was 25' higher, I'm ok with not being right on the river!

Gary T - so far she likes it.  Haven't been able to talk her into to touching the fish yet!  Maybe we'll get there by the end of the summer!


Ok, so here's the first round of questions.
We're going to install a pier and post foundation.  From the plans, we'll go with 8" concrete piers.
1) what's the best concrete to use for the piers? Normal quikrete? The high compressive strength variety?
2) we plan on pouring a 16" diameter footing 8" thick (per the plan) and ending up with 3' of the pier below ground and 1' above ground.   The frostline in Oklahoma is around 18" deep.  This should be sufficient, right?
3) we're planning on adding a porch to the back and this will add 5 more piers to the foundation. I'm calculating that we'll need to mix around 65 bags of 80lb in total.   I'm thinking it might be worth investing in a small motorized concrete mixer.  Any recommendations here?

Thanks in advance!


I've been reading the CP forum for about a year now, and one of the themes that crops up with some regularity is the pros and cons of a post and pier foundation.  The Dons regularly advise builders to consider a continuous concrete perimeter foundation, either poured concrete or cinder blocks built on a concrete footing.  The bottom line is that post and pier foundation is not in the residential code.  An inexperienced owner-builder can avoid a world of potential problems by following the prescriptive code and going with a perimeter foundation.

That said, post and pier foundations are popular because they are usually fast and affordable, and are adequate in most situations.  The onus is on you and I as the owner-builder to ensure that the proposed plan will adequately support the structure and anchor it to the ground sufficiently to withstand the slings and arrows that the earth and atmosphere will hurl against it.  Some county jurisdictions may actually require an engineer's stamp to ensure that the proposed foundation is sufficient.

This is all a roundabout way of getting to the point that to me the 16" diameter for your footing seems rather small.  That equates to just 1.4 square feet of load bearing area, which depending on the weight of your cabin and the number of piers, could be inadequate in soft soils.  If you've done some calculations to confirm that your piers can support the entirety of the structure then I needn't be concerned.  if you haven't yet done those calculations, you should.  Estimate the total weight of the cabin, divide by the number of piers, and divide that by 1500 lbs (the minimum load bearing value of poor but buildable soil) and if your number comes out less than 1 square foot then you should be OK.  Personally though, if I had any doubt I would make the footing a larger diameter.  A footing and pier made with rebar and concrete is going to be way stronger than the soil below.

Edit to add:
QuoteI'm thinking it might be worth investing in a small motorized concrete mixer.  Any recommendations here?
Buy one!   ;D
My cabin build thread: Alaskan remote 16x28 1.5 story


I don't like to endorse "Blue Tools" from a particular big box store but I've been abusing the hell out of an electric Kobalt mixer for over 10 years now... I've mixed close to 350 #80 bags for my project this year alone.  It'll handle 3 bags at a time which is pretty impressive for what it is.


Thanks for the info!  I see what you're saying about the load distributed over a small number of piers/footings.   I'm confused as to why the plans would suggest such if that isn't sufficient. I think 16" was on the high side of what the plans suggested.  I also noticed the plans just showed piers/footings on the perimeter of the foundation, with none in the middle.  I could put an additional 3 in the middle to add more support.   In regards to your formula, is there a rule of thumb for calculating the load of a 1 1/2 story cabin?



 w* cant wait to see the progress. Im in OK also.
"Chop your own wood and it will warm you twice"
— Henry Ford


A typical foundation would be a full perimeter foundation on a continuous strip footing. The footing is typically 16" wide and 8" thick with 2 strands of 1/2" rebar 3" off the bottom. Block or concrete walls up to the floor system. In your case I believe 18" below final grade is the depth to the bottom of the footing. Your local building department has those depths. This helps avoid different settlement, provides better support for the building (there aren't as many opportunities for those oopses of a heavy load from above coming down right in the middle of a girder that wasn't designed for it), and most importantly the foundation walls provide bracing for the structure in wind or seismic that a post does not.

For loads, chapter 3 of the IRC spells out design loads, many are standard, floors 40 pounds per square foot live load + 10 psf dead load. Roof (use the horizontal square footage) 10-15 psf dead, snow is your live load, check with the building dept for this local design load. Tally them all up and that is the design load. Then, in the case of piers especially figure out the load distribution... ah, they carry different loads, differential settlement  ;)



I'll walk you through the numbers Don_P provided.  For this exercise we want to err on the side of caution, which means overestimating rather than underestimating the weight of the structure.  Your 20x30 building has 600 square feet.  The dead load that Don_P mentioned is the weight of the building itself, then you need to add the live load, which is 40 lbs per s.f.  Using 55 lbs per s.f (psf) that equates to 33,000 lbs for the first floor.  For the half story, use a 30 lb live load for sleeping areas.  Again with a 15 lb dead load and assuming 600 sf, that equates to 27,000 lbs.  If there will be an open ceiling for part of that then scale back the square footage accordingly.  Finally, for the roof you need to account for the dead load and the snow load.  Based on a nation-wide snow load map, most of OK is in 10 psf area, but parts to the northwest have 20 psf snow load.  Allowing 1 foot overhang for eaves all around, the roof has an area of 704 s.f.  Using 20 psf for snow and 10 psf dead load, the design weight of the roof is 21,120 lbs.  Adding all that together gives an estimated load of 81,120 lbs.

Different soils have different strength characteristics.  A house on solid rock will not move whereas a house on clayey soil runs the risk of sinking unless the foundation is large enough to support it.  If your cabin site has poor soil, then a compressive strength of 1500 lbs may be all that is warranted.  That means that each footing should be large enough so that the weight bearing on it is distributed to keep the ground pressure below 1500 psf.  For a building weighing 81,120 lbs, that means you would need at least 54.08 square feet of footing.  At 16" diameter that would mean putting in 39 piers.

Your land may have a much better compressive strength, but without having it tested you don't really know.  Then there is the fact that the load will not be situated on every pier evenly.  One pier may see a load of 1200 lbs and the adjacent pier could see a load of 2000 lbs or more.  If that pier starts to settle, then you'll be looking at having to repair damage to the building as well as come up with a way to prevent further settling.

If it were me and pier and posts foundation was my only option, then I would look at increasing the footprint of each pier significantly.  Or dig into the engineering and calculate it exactly.  Knowing what your soil strengths are would be a good place to start.
My cabin build thread: Alaskan remote 16x28 1.5 story


I thought I'd mention that I will be doing post and pad foundation for my cabin in Alaska.  I'm dealing with potential permafrost and a traditional concrete perimeter foundation is both impractical and could result in thawing the ground. 


I wouldn't rule out post and piers for your cabin, but you really need to delve into this issue to ensure that all the time, money, and effort that you invest in building it is not put to waste.  You do not want to end up like this guy... http://countryplans.com/smf/index.php?topic=4952.250

Plastic footing forms like the Bigfoot have a 24" diameter and would effectively increase your footing area by 225%.  Installation is usually done with an excavator or backhoe, and backfilled around once the concrete is in.
My cabin build thread: Alaskan remote 16x28 1.5 story


Wow! That's a wealth of information within those few posts!  Thanks guys.   Sounds like we'll be doing a little more figuring on our pier and post design.    We're pretty set on pier and post due to the grade that we're building on.   It's not really step, but roughly a 4-5 drop over 30' or so.  I talked to a DEQ rep regarding our septic tank and due to our proximity to the river, he is requiring that we have a soil profile test peformed instead of a perc test.  So as soon as we get that, we should have much more information on our soil quality.  I'll be sure to update here once we get that done.   Thanks again everyone!


Quote from: Eclour87 on May 24, 2016, 06:32:18 PM
  We're pretty set on pier and post due to the grade that we're building on.   It's not really step, but roughly a 4-5 drop over 30' or so.

That is not at all outside of what can be done with a conventional foundation. A post frame building would structurally be a better choice than pier and beam.


Don_P - what is post frame building and how does it differ from pier and beam?    What about having a concrete perimeter poured and then placing posts on top of it (using brackets sunk into the wet concrete to hold the posts)?   If the perimeter footing was 1' wide, that'd give us roughly 100 ft^2 of area for the cabin to sit on.  As a side note, I ran the calculations ChugiakTinkerer posted using our dimensions.  Our loft area will be 210 ft^2 and the snow load for eastern Oklahoma is 10 psf.  So with those reductions, our total estimated weight comes out to 56,350 lbs.  Assuming 16" circular footings, I calculate that we'd need ~27 piers.   That's quite a bit more digging than I'd like to do.  It's amazing how quick something like that will change your mind. : )


Quote from: Don_P on May 24, 2016, 09:51:18 PM
That is not at all outside of what can be done with a conventional foundation. A post frame building would structurally be a better choice than pier and beam.

I think I understand what you're saying now.  You're suggesting a conventional foundation with normal post frame on top, right?   I was thinking you were speaking of "post frame building" as a different type of foundation altogether.


Think "pole barn". What we've talked about so far is resisting vertical loads, the weight of the building, occupants and snow bearing vertically on the soil. The other direction that a foundation needs to resist loads from is horizontal, or lateral, coming from wind or seismic. Pier foundations do not resist lateral loads well, which is why the building code requires that pier type foundations be reviewed by an engineer. When I've asked engineers about the pier and beam foundations shown here they have said no, (I'm being polite). There is really nothing preventing the piers from tipping over if the building gets loaded from the side as in a high wind.

In a post frame, the posts run unbroken from footing to the top of the wall. The wall is sheathed. There isn't a joint, or hinge point, at the floor to post connection. The walls are bracing the posts. This is also outside of prescriptive code, in other words, engineer required. The engineers no turns to a yes here though... this does work. This is a quick sketch of how that works;

Prescriptively a full perimeter foundation is the standard.

That is the full perimeter footing with block or concrete walls topped by the floor system, braced house walls on top of braced foundation walls. Other types of prescriptive foundations are pier and curtain wall and permanent wood foundations.

Another non prescriptive method is somewhere in between, full strip footing with larger masonry or concrete piers tied to the footing steel. The corners are at least as wide as tall and provide better overturning resistance


I'm finally getting around to posting some update pictures.  It's only been 8 years!  Life happens, but we're still at it!    We built the majority of the structure in the summer of 2017.  Since then, we've been slowly, yet distractedly working on finishing it between job changes, moving, the pandemic, etc.  Anyway, hope folks enjoy the pictures!