Concrete Footer Design

So, now it's time to design the concrete footers. This project is what's known as "dry stack", which means the concrete blocks don't have mortar between them. What - you ask? What keeps the wall from moving and collapsing -- rebar, placed vertically, running thru the blocks from footer to top of wall. The rebar is anchored in the footer and for my taste will go thru most every block. To make this all fit the vertical rebar will be on 23" centers. After the wall is built, you come back and pour concrete into all the holes that have rebar in them. This locks everything together and makes for a very strong wall. Then you cover the outside and inside of the wall with about a 1/8" thick layer of surface bonding cement; which is just a fancy name for concrete mortar with fiberglass in it. After it's dry, it looks like stucco. I'm not sure if it's totally waterproof at this stage, but if not I'll make it so with something else.

Dry stack walls are a little more height critical than mortared walls, so the footers have to be at the right height, so the wall will end up the desired height. In the pic above there are five "steps" in the south wall (each stepdown is 7-5/8", same height as a concrete block). I had to make sure they were done right; so I measured, calculated, measured again, calculated again -- must have done this 3 or 4 times until I was satisfied. In the end I know exactly where (how high) to put my forms for the concrete footers. All the walls will be done this way; I just used the south wall as an example.

Another thing I wanted to add is there will be a foundation drainpipe (4" perforated PVC pipe) that runs along the bottom of each footer. For this to work the footer trench has to slope fairly evenly from the high side to the low side, so the pipe will drain well and not load up with sediment.

I know the numbers in the pic are small but numbers across the top are every 10 feet of house length; numbers down the right side are on 7-5/8" intervals. Each row of squares represents one layer of concrete block.