Courtyard wall questions

Hiya, Gonna start gearing up to build a courtyard wall at the entrance to my house. I'm planning on using adobe and am pretty familiar with that aspect of it. I'm curious to know where I can find out what my frost line is? Silly question I know but every garden center, home supply, etc... company can't give me a definite answer. I'm in ABQ New Mexico and as near as I can tell, it's 18" but not sure. I assume the top of the footing should be no higher than 18" below grade correct? Finally, looking at a 4-5' wall. Was thinking a 6" thick foundation would be enough....thoughts?
Thanks much, cc
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I'm planning to buy the bricks. I don't mind do it yourself but making all my own bricks just might put me over the top :) I hadn't thought to call the building inspectors. I'll do that. By the way, I didn't think the footer had to be so wide. All the literature I've read so far (a couple books on building with adobe) suggested 3" on each side. Adobe comes in 10" wide bricks so it would mean a footer of 16". Of course, these were for walls that were going to be used in a home vs. a free standing courtyard so perhaps I should go wider. Thanks for the help! Cheers, cc

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I was surprised when I looked at a USDA zone map. Most of NM is in zone 6 same as KY. Sure seemed warmer than that during my brief stay there.
18" below grade to the bottom of the footer is correct here, zone 6. Your goal is to prevent freezing water from heaving your footer. You could call your local building inspection department for a definitive answer. Do it from a pay phone if you wish to remain anonymous.
Six inches might be enough. I'm not sure about that. I would use 8" for a wall that tall. I do know it needs to twice as wide as the "bricks" you plan to lay. A 12" adobe should be centered on a base that is 24" wide (front to back).
Are you planning to make you own or buying ready mades?
Colbyt
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