One thing I forgot to add is that I live in Southern Utah, in the desert. Very hot and dry, not much moisture. I'm not an expert, but I'd imagine that saturation behind the wall wouldn't be an issue. Also, I guess frost heave would not be an issue. Hardly ever freezes here, and it doesn't go deep.

This post was edited by matt_m on Thu, Jun 6, 13 at 14:48

20" high with all of the conditions that you describe will need the services of a professional. "Just" a 20" tall wall holds back tons of soil and must be engineered properly. You will need to dig down low enough to pour a footing, and you can not pile any dirt at all on the roots of your trees or you will smother them. Yes, you will need to account for drainage. Even in a dry climate. Sudden rains that are common in dry climate areas are actually riskier than are uniformly moist soil conditions. You will also need to get a permit and have the whole thing inspected. It's for your safety, and that of your neighbors. If not built correctly, a retaining wall can kill someone when it collapses.

Do an accurately dimensioned, rough plot plan of your property and have an eng. design the wall.

I would incorporate the steel fence posts into the poured wall, it will never move. That is if chain-link is the fence you go with. All good points from Green and snoonyb. Drainage is probably more important in the dessert than here if what I have seen during those flash floods in Arizona occurs where you are. Man I wouldn't have believed it if I hadn't seen it with my own eyes.

I really appreciate all of the advice. We are situated on a hill, near the top -- in 10 years, flooding has never been an issue, but it has with people who live further down the road.

I talked with over a dozen people over the last few days (one an engineer at Sunroc), and it seems like the winning idea is a 8" - 10" deep footing, 12" to 16" inches wide, with a 6" block wall or concrete wall on top of that, centered on the footing, with rebar uprights every three or four feet, as well as at least two bars the length of the footing and at least one bar lengthwise in the wall. No soil added around the trees! Just running the wall in a straight line down the property line.

And most of the builders I talked to today were all for either putting the posts directly in the wall as it is being poured (to extend down into the footing, too), or insert them into the block to a depth of 24" and mortar around it, as well as filling in all the cavities that have rebar. Several of them said it wouldn't hurt to fill all of the cavities with cement, but at that point, I might as well pour a concrete wall!

One builder said that if, later down the road, I grow tired of chain link, I can always take the fabric down, saw the posts off flush with the top of the wall, and just continue on up with more block. Sounds like a cool option.

One thought I had was this -- if I build the wall on my neighbor's side of the property line (he doesn't seem to care one way or the other, especially since I'm doing all the work and paying for it), is it then his wall? Not sure about how that would affect things.

I took something useful from each reply. Again, thanks for your help!

This post was edited by matt_m on Sat, Jun 8, 13 at 0:15

As for building anything on a neighbours property well that requires a legal answer which I can't offer with confidence. But from experience I can tell you it is definitely not something I would do. You current neighbour may be fine with it, but if he sells next week the new neighbour might not be. Imagine the new guy asking you to move the wall. Or tearing it down because after all it's on his property. What if some kid falls off the wall and is injured?

Search property line issues on the buying forum here. All sort of nightmares to read about.

If anything I would build it 6" on my side to prevent any issues. I won't let my neighbour build on my side no matter how good the intentions are.

I believe technically it would become his and he may not like it himself next week and since it is now his.................

Drainage is the most critical portion of the wall construction, and it's what your plan is missing. You will need getotextile fabric, gravel, drainage tubing, and some place for that drainage tubing to exit. through the wall. Without weakening it.

And, of course, the permit and inspections from your city. To get that permit from your city, you will also have to have plans that they can look at, probably stamped from an engineer or LA. Those plans WILL require drainage to be accounted for in the cutaway.

"Posted by matt_m (My Page) on Sat, Jun 8, 13 at 0:11
I really appreciate all of the advice. We are situated on a hill, near the top -- in 10 years, flooding has never been an issue, but it has with people who live further down the road."

Engineering is an exact science, based upon assumptions, and in that light an engineer is required to provide a design that budgets for and meets the minimum design criteria for the area in which you reside.
IE., overturning moment; at heights over 6', wind governs, so the design will budget for the installation of privacy slates or removal of the fence fabric and wood panel placed between the steel posts, which is a common design alternative.

"(one an engineer at Sunroc)"

I would urge you to seek the advice of a private professional civil engineer.

" the winning idea is a 8" - 10" deep footing, 12" to 16" inches wide, with a 6" block wall or concrete wall on top of that, centered on the footing, with rebar uprights every three or four feet, as well as at least two bars the length of the footing and at least one bar lengthwise in the wall."

With the exception of the 2nd piece of rebar in the footing, this is a typical "garden wall", not a retaining wall. Generally speaking, a wall less than 2'6" in height "is not" considered to be retaining.

No soil added around the trees! Just running the wall in a straight line down the property line.

"putting the posts directly in the wall"

Which would be ok, except that you have something called "cost", which is the required embedment of rebar in masonry walls, which is 2" and cannot be attained using 6" block.

"I might as well pour a concrete wall!"

Not hardly!

"One thought I had was this -- if I build the wall on my neighbor's side of the property line (he doesn't seem to care one way or the other, especially since I'm doing all the work and paying for it), is it then his wall?"

If you are, indeed, contemplating this, you need to obtain and easement based upon the final wall design, because if you take a "disney land" approach to this, if you have a lender for you property, you'll find them defending ONLY their intreats and NOT YOU.

There are prescribed and restricted "drain fields" which are designed to protect "downstream" home/properties from from natural occurring moisture from affecting that habitability.
Those exist in your case and must be addressed.
It's called "hydrology", and will be addressed by an engineer.

"Not sure about how that would affect things."

You, in addition to an engineer, might want to have a chat with a real estate attny.

Thanks for the additional advice. I was talking with my wife last night, and we are of the same mind -- just build it on our side of the property line, avoid the hassle of any legal issues.

What I meant by a 6" wall, is that it will be 6" thick. The wall itself will be at least 2' high, but the more I think about it, the more I'm thinking of just going with a 6' high block wall, and just build it at my leisure over a period of time.

Thanks again for the help.

Building a 6" wall on your property line should follow a surveyors map.
You still have the hydrology to address and while upstream is the desired method, which will involve your neighbor, you can leave open head joints addressing the resulting drain field within 3' of your dwelling.
A 6" CMU wall is 6" OD with 1" walls and 4" ID. Centering a 2" chain link fence post leaves 1" to place a 5/8" rebar, which leave 3/8", far from the 2" cost required.The rebar coarse in the top row of block is solid grouted and called a bond beam.
Permits require periodic inspections and have time limits as well as renewal fees.
Cold joints result in weak structures.
Deteriorated rebar will result in remedial action required.

Thanks, snoonyb. What I meant by a 6" wall, is that I am now thinking of foregoing the chainlink on top of a short retaining wall, and just going with 6" block for the entire height of the wall (6'), with pilasters.

I didn't include drainage in the discussion, but I have a couple of neighbors who built block walls around their property, and we discussed the drainage pipe, and gravel backfill. They actually showed me their plans (approved by the city) to give me a better idea of what they were talking about. What's cool is that one of the neighbors had to retain even more dirt than I do (3' instead of 2'), so I'm thinking his plan should be more than adequate for my wall.

This post was edited by matt_m on Sun, Jun 9, 13 at 18:47