I’m planning to replace a simple three rail fence at the front of my lot with a stone wall for more privacy and to cut down road noise. I plan to make the wall from concrete block with artificial stone facing.
Figuring out how to build the wall itself is easy, but I have not had much luck finding any information on creating an appropriate footing for such a wall.
The wall will be 5 to 6 feet high, and is about 100 feet long. I plan to make it with something like 6 inch block faced with the artificial stone. I live in the Portland, Oregon area so frost is not much of a problem. I believe code for houses is an 18 inch deep footing but I’ve never heard of it freezing more than 4 or 5 inches in the worst of years.
I thought of just doing a concrete footing 18 inches or so wide one block height below grade and using 8 or 10 inch block filled with concrete for the first row, rebar every 4th hole or so and a couple of horizontal rebar in the footing concrete.
However, I am concerned about tipping forces on the wall. With houses, the load is shared between multiple footings and mostly vertical even with horizontal forces on the house. With a wall, there is just the one footing and any horizontal force on the wall will tend to rotate it and tip it over.
Any ideas? Is this an adequate footing? Or do I need to make it deeper, like maybe two rows of block, so that it will be embedded further in the ground and resist tipping more like a fence post? I’d typically put a post for a fence this height down 18 to 24 inches deep, but this wall is going to be a lot heavier than a wood or vinyl fence and I would think the horizontal forces, especially in an earthquake or such, would tend to cause it to tip a lot more readily.
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My thoughts are that you need posts going about 3' into the ground every 6' for vertical stabilization. You can lay the block over them. Use something stout like 1" rebar or 2" heavy pipe for the posts. You need posts even if you were to place the wall deeper in the earth to keep it from breaking over in high winds. Typical rock walls are tapered wider at the base, maybe you could do the same by starting 3 blocks wide at the bottom tapering to one at the top. That would be a lot more stable.
I think your intuition is correct, an 8" x 18" footing with the top 8" below grade would be entirely adequate for anything except possibly an earchquake. There was an article in FHB after the Northridge quake in LA that said California was strengthening the requirements for block fences in seismic area. IIRC, the new requirement was rebar every 4', which would be every 6th hole, and all cells fully grouted.
If you have room, you could lay it out as a zig-zag instead of a straight line. That way each short section of wall reinforces the two adjacent sections. Block walls are very strong in racking, so whichever section is under racking load helps hold up the adjacent sections that are seeing overturning load. This idea, relatively short, mutually supporting walls, is a design requirement for adobe houses in some jurisdictions.
With respect to overturning force, I don't know how to evaluate the benefit of having two courses of block below grade instead of just one, but I would point out that the cost is only 75 blocks for a 100' fence. (Plus the extra mortar and rebar, of course. (And the extra digging.)) Doesn't seem like a large percentage of the total cost for this project.
Its the digging that is the issue - i've had the utilities located and phone, cable and power (primary power - like 16,000 volts worth) run right along the side of the fence location. The power is deep enough to not be a problem, but because of the phone and cable I'll probably have to hand dig about 50 feet of it!
How close do the utilities run? Out here we have a service that marks the utilities and they tell you to give 18" to each side of their marked lines. You could always move the wall a bit so you dont have to hand dig just go rent a mini excavator. Dont forget the razor wire at the top.
Undulate...Your wall will be more beautiful, and far stronger.
Don't know what kind of soils you have, but in general, I would trench about 18" deep and pour an 8" deep footing with steel. If you have wet or poorly drained soil, you have other work to do.
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You could add some buttresses. Would add strength and interest to the wall. Many walls have fatter stone 'pillars' or 'posts' along the run that buttress the wall.
Or, I wonder if you could periodically deepen your footing along the run to provide a better 'bite' into the ground.
A couple of things to be concerned about:
1) Frost line aside it is important to dig down to nice compacted non-organic soil(clay)
2) If the grade changes you may need to step the footings.
3)would definitely put rebar in the footings with pins coming up into the holes in the block then grout them in to unify the footing and the wall
Sounds like a fun project because stone walls make good neighbors :) Don't forget the remote controlled gate.
It might be a good idea to put joints in the wall every 10 feet or so.
What gate? I thought I'd just put a solid wall all the way around - that should make for excelent neighbors!
CD:
Check your local building codes.
Here in LA, for walls UNDER 3 feet that are not retaining, a very simple footer will do. It has to be 1.5 feet if it is a double wide course and a full 3 feet if a single wide course.
For walls OVER 3 up to 6 feet that are not retaining, my recollection is that the sizes are doubled.
Your local Building and Safety is the source for this information. I will guaranty if you pull a permit, you will find out very quick.
Boris
"Sir, I may be drunk, but you're crazy, and I'll be sober tomorrow" -- WC Fields, "Its a Gift" 1934
Probably a good idea - but if I have to put in a 6 foot wide footing, there won't be any place left to plant anything.
I don't follow that. If you put the top of the footing 18" below grade, you can plant lots of things over it.
Not a 6 foot wide footing. Lemme give you an example. You have a wall of 9 inch CMU and it is 3 feet high. The footing would be 18" deep and 18" wide. Got it?
If you don't want to go that wide, the footing is 3 feet deep and 9 inches wide.
This was LA Code the last wall I did a few years ago.Regards,
Boris
"Sir, I may be drunk, but you're crazy, and I'll be sober tomorrow" -- WC Fields, "Its a Gift" 1934