Little House pier questions

[Pa_Kettle]

We purchased the Little House plans kit last year and are now about to start building.  I've read and re-read all the literature and have a pretty good idea about how to procede, but I have a few questions (so far ) about piers/footings.

First, we are building in south-central Missouri (Ozarks) on fairly rocky soil.  I believe our frost depth is 18" - 24".  I haven't done a DIY soil sampling yet, but I will be doing it soon.  I am assuming we have well draining soil.

The deck blocks I have available are a simple (chopped) pyramid with a 4x4 recess in the top.  Now, I know that deck blocks with straps that allow nailing of the 4x4 are suggested.  Is this for uplift protection?  How much protection does the small weight of a deck block add?  Is bolting something like a Simpson "ABA", to the deck block, worth all the drilling?

Also is a standoff of the vertical 4x4 from the concrete important?  Looking at my Simpson post base choices http://www.strongtie.com/products/categories/post_bases.html , I see post bases that are essentially a "U" that bolts to the concrete and others that have a 1" standoff.

The plans show using a 16x16x2 paver under the deck block.  Should I use crushed rock under the paver or if I use crushed rock can I skip the paver?  Am I asking for trouble if I don't dig down two feet or deeper?

I've toyed with the idea of pre-casting some taller (18") 8" dia concrete cylinders with something like a Simpson "PB" or "PBS" but those suckers are going to be very heavy.  I don't have many resources at the building site (i.e. water) so I want to stay away from trying to mix concrete on site.  Help!

Thanks,
PK

[glenn kangiser]

Hi PK,

How about using the pressure treated pier option - dig holes and put gravel around pressure treated posts.  Pressure treated plate on the bottom if I remember right.  Don't have my plans with me tonight.

http://countryplans.com/foundation/index.html

[John Raabe]

If you are in rocky well-drained soil you may not need crushed rock under the pavers and can bear the deck block right on the material itself. This will be your footing. If this footing material drains well then you will not get frost heave and don't need to get down to frost depth.

A concrete or PT wood pier gets you down deeper and provides a better anchor against uplift (wind) and earthquakes but many small buildings in protected sites will never experience these forces in their lifetimes.

The more you have invested in your house the more sense it makes to protect against these small possibilities. If you are going to put a few hundred thousand dollars into a project then it makes sense to build a fully reinforced and engineered concrete foundation with all the permits properly documented and signed off. By doing this you not only protect the building but your investment.

The opposite is also true.

So, in the Little House plans, I attempt to show options that allow for a good and adequate foundation for a simple low-cost structure.

[Pa_Kettle]

Ok, thanks for the quick reponses.

Glenn your right about the PT base (2x10), but I don't want to put wood underground in this structure.  Just a personal preference I suppose.

I think I'm going to go with the deck blocks I described above, with a Simpson "ABA" bolted to the top.  I'm going to dig a few holes this weekend to do the DIY soil test and that should give me an idea of whether to use pavers or deeper gravel.

This is going to be our (hopefully) temporary shelter and then a guest house.  We will live in it long enough to be sure of where to put the "big" house.  The big house is...  wait for it... a Mike Oehler PSP house!  We've got all three of his videos and I think he is a hoot.  Down the street from our land is a wood mill so I think we are going to go with square beams, but other than that it should be like Mr. Oehler describes.

PK

[glenn kangiser]

Way Cool, Pa.

Are you going with the EPDM material over the roof as he now recommends?  I would go out much farther around the sides where there is water runoff as Bruce mentions.  Consider perimeter French drains in possible problem areas too.

Please keep us posted on your plans, questions, methods and comments.

[Pa_Kettle]

Glenn,
We haven't gotten into those exact details of the earth house yet.  We've sketched out the basic floor plan, which is three shed roofed sections approx. 16x16.  Each is offset front to back and/or up and down to each other to give a nice sense of split-up areas without any real interior walls.

Of course even that may change once we pick a spot to put it.  We want to live out there at least one full set of seasons to get a good idea of where the best spot to build will be.  It's possible we will end up with a "ridge" house.  We have one spot on our sloping property that gets flat and actually rises just a bit before continuing to drop.

I've seen the pictures of your house, which is amazing btw, so I know to take any advice you give about the process to heart.

Thanks,
PK

[glenn kangiser]

Sounds great PK.

I'll try to help you by a few of the bumps in the road when you are ready to go.  I had doubts at first-- you can't believe it will really work-- sounds too simple and cheap, although quite a bit of work.  I figured --what the heck - I wouldn't be out much.  It just became a challenge from there.

There are things I would do differently now but only minor changes to prevent moisture in a couple of places.  They are still pretty easy fixes.  A good backhoe - even if it's old and used can be a pretty good friend with an underground house.

[Pa_Kettle]

Glenn,
Thanks for the offer of help.  I'm sure we will need it.

We have a neighbor with a backhoe who is going to dig the footing holes for the little cabin.  Our soil is so rocky I can't imagine trying to hand dig them.    I'm sure we will ask for his help digging things out for the earth house.

PK

[Pa_Kettle]

I have a frozen sample of our building soil in front of me.  It looks pretty good.  No real expansion.  The wet settling stage ended up with almost all the material at the bottom of the container.  So I guess the soil's clay content is fairly low in our building site.  

I've decided to have crushed rock brought in to put under the deck blocks.  After thinking about it, I figured filling the footing holes with gravel would be much easier to get flat and level than the pavers.

PK

[Pa_Kettle]

Just to be clear.  If I put 16"x16"x8" (or deeper) rock in the footing holes, I _don't_ need to put pavers under the deck blocks.  Correct?  I just place the deck blocks on the (well tamped) crushed rock and back fill around the decks blocks, right?

PK

[Amanda_931]

In my soil tamping gravel for a foundation means pounding away with something smaller--and probably heavier--than one of those square iron jobs with a handle that they sell for the purpose until the note sounded by the blows changed to something that was almost ringing.  

(Actually, IIRC, even a 5-foot length of 2x4 hits quite a bit harder than those tools with the 8" square on the bottom.)

[glenn kangiser]

I'm not sure what the minimum is for the piers but the pavers will give you a wider base under the blocks and in turn, more support and resistance against settling.  It could vary widely with site conditions so a positive answer is hard to give.  In general the softer the soil, the wider the base required.

In my soil a 4x4 would be sufficient as far as supporting the weight would go.  Claystone - Nearly as solid as rock.

[John Raabe]

If you have crushed rock in a footing (not round pebbles) it will lock together and not compress or settle. This, in effect, is a monolithic material that will work the same as concrete for downward pressures. Then you can use the same rule of thumb that is used for unreinforced concrete - downward forces can spread out over the underlying soil at a 45º angle.

Thus if you have a point load from a post or footer that sits on a 12" pad of crushed rock, make that pad 12" wider than the pad and the full area will be serving as the footprint or snowshoe to distribute the load to the earth.

[glenn kangiser]

Now that is a good piece of information to stow away in my rusty little brain.  Thanks, John.