We are about to begin our home using a pier and beam foundation.
Sources tell us that we need to use a pad no smaller than 16x16x8 with our 8x8x16 concrete blocks.
The problem is that we can't find a source for this size pad. So, we have decided to make our own pads.
Instead of building forms to make these pads we had an idea just not sure if it will work.
We have thought about digging holes 16x16x8 and lining them with visquine plastic and then pour the concrete into these holes to form the pads.
Then center and place the 8x8x16 blocks upon these pads.
Will this work?
Not what's shown in John's pictures. But weight of the building counts, too. and the fact that you are wanting to use concrete blocks for your posts.
Two companies have been mentioned here.
Third link is the second company.
I'm waiting to hear how many million dollars these would to cost me--second link tells you how many to buy (but not what to do if it comes out something like seven--and not how your beam sizes are going to change if you use the minimum):
http://www.foottube.com/index.htm
http://www.foottube.com/FootingTube_Cat04.pdf
http://www.fab-form.com/default.htm
There is no reason you can't pour your own footings. Better to err on the larger side as far as size goes. I don't think the plastic is necessary - most footings go directly into the soil. Vapor barriers are commonly used under slab floors to stop moisture though.
As I remember, you didn't need an engineer so spacing is up to you. If you have any concerns about the strength of your pad under your blocks you can add some reinforcing wire or rebar to each footing to help tie things together. I don't see any problem. If you wanted to form piers with wood you could install anchors in them and forget the blocks. That is what I did on my shop footings. The bottom of the form is left open and continues down to the footing. It is visible in this picture at the bottom of the steel post near the back of the wood wall.
(http://us.f3.yahoofs.com/users/41fdb066z210983f4/8ac1/__sr_/8239.jpg?phzPcoCBE55lgPEA)
Rebar can also be added vertically. There is also no reason your design with the blocks shouldn't work. Just trying to give you different examples. Rebar could also be added in the blocks to tie things together if there were concerns.
In addition to what Amanda and Glenn have said, here's one more thought...
Pouring your own footing in the bottom of the hole will actually be better than using a pre-cast pad because you can be sure it will conform exactly to any uneveness at the bottom of the hole. You should still try to get the bottom as flat as possible and remove any loose dirt. If you can't get the bottom flat because of rocks, then you could drop in a few inches of gravel and tamp it down.
Bart
Thi is a big THANK YOU to Amanda, Glenn, Bart, John, and to anyone else that I may not have mentioned that has been so kind in responding to my questions.
I'm a new member but I'm already hooked to the forum.
This will be our first big building project assisted by a group of family and friends who have all had experience in building and remodeling.
They all are amazed and think that we are a genius when we come up with some new ideas and they work.
We just don't tell them where our source of information is located.
I'll never tell ;)
You've probably already read the free report I did on pier foundations: http://countryplans.com/foundation/index.html
Here is the drawing of a similar footing.
(http://countryplans.com/foundation/img2.gif)
Glenn is right, better NOT to use poly here as the bearing and cure will be better sitting right on the ground.
PS - Those dotted lines are 1/2" (#4) rebar.