tabber,
You may not be getting a response to your question because it is a little more complicated than a simple ratio that would require a certain footer for a given height. A demo program I downloaded from Retain Pro was helpful to me to assess the walls I'm building.

I live in Arkansas and around here there have been a lot of DIY block walls built. Most of them have failed or are in the process of failing. Best I can tell, those that stood up over the years were built on a substantial footer and the block cavities have rebar and concrete. Steel stubs up from the footing to lock the wall to it in many of the block cavities. The good walls that are over 3 feet high were made with 12" block and they all have a system to prevent the ground behind the wall from becoming saturated with water. Not a cheap thing to construct.

Lately, a lot of homeowners have built walls using the modular blocks that lock together. Close attention to the details will bring most DIY walls of this type to a good result. But they are what they are. If you like the look, it's not a bad way to go. If you want a true vertical wall that can have a finish of stone , tile, or some other material, then you have to look elsewhere.

Timber walls are another possibility that some choose. But they aren't a permanent solution. The life span of a timber wall is also shortened if you have a long season where the ground is warm and you garden on the up side keeping the ground wet and fertilized.

In the end I chose to do poured concrete walls. Most would say that this type wall is beyond a DIY project, but in my second year of wall building, I would say that there are no special skills needed, nor is the cost of tools that much more than needed for other types. One might call it an advanced DIY project, not for a beginner. I didn't have experience with concrete when I started but I did have a lot of DIY projects and was well experienced in working with wood. Most would do well to keep their wall heights to 3 feet and under.

Keep in mind that down here the ground does not freeze more than a few inches deep, something that might be a major problem for those in colder areas.

I now have about 200 feet of wall up with another 125 to go. One of the things I like about poured concrete is that I don't have a lot of really heavy lifting to do. There is a lot of labor, but the form panels and other materials are not much more than 20 pounds, something an older man can handle.

James

I think I just sent you a separate email but if you could reply to the post instead to continue the thread. how far apart are you putting your vertical rebar in your wall?

dorlando,

I don't seem to have mail from you. As far as I know the link on "My page" is still active.

I no longer monitor this site like I did in the past, and the amount of content I am willing to provide to gardenweb has been scaled back.

I haven't done an update this year on my wall project. Not much has changed in my method, except I worked out a nifty way of doing the forms for steps.

Here are a couple of pages that I did last year ....

http://www.geocities.com/pls8xx/construction.html

http://www.geocities.com/pls8xx/update.html

The vertical rebar consists of short bars in the footer that extend about 8 to 10 inches into the bottom of the wall spaced about 2 feet apart. These are positioned more to the backside of the wall. In addition longer vertical rebars are set in the footer about every 6 to 8 feet that extend to near the top of wall. These are used to hold the horizontal rebar and are positioned slightly toward the wall face. Walls 3 feet tall and above get a beefed up steel and footer treatment.

Sorry, that I didn't reply sooner. I was away over the weekend.

I haven't yet started my wall, so I don't have an answer for you.

COntact your local building codes dept. When I did they said concrete foundation should be 42 inches deep to avoid frost heave. Probably a little less deep in your area, but that is still deep! Probably not what you want to hear, it means renting an excavator for a day, but you also don't want to do all that work and have it buckle on you due to frost heave. Your local building codes dept will have the answers for you and they are free.