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fence on top of retaining wall

nash's picture

hello, looking for ideas on how to attach 4ft fence on top of concrete Allen block retaining wall that I want to build.  Retaining wall at max height will be 3ft.  I live in nyc area.

Can it be done ?  Do i need to use concrete cinder blocks or poured concrete.  Any suggestions will be a great help.


thank you

(post #72635, reply #1 of 27)

We did one by using tall wooden fence posts and then face mounting the fence rails to the post. In that case, the retaining wall was 4 X 6 timbers with 6 X 6 posts holding the timbers. The fence posts were sunk in the ground and then fastned to the wall.

If you do poured concrete you can probably put the fence posts in the wall (we have one like that now), but I suggest figuring out some type of sleeve system so that the posts can be replaced. I'm dreading the day one of our posts snap off.

(post #72635, reply #2 of 27)

I'm not sure about Allen block..but the Mesa wall system we use has a big hole in the block. We insert a 2-1/2" Galv. pipe into that hole and fill the hole solid with either concrete or item 4..

Then U-straps can be used to screw on any type of fencing...

(post #72635, reply #3 of 27)

Allen block won't hold back 3' of earth for long ..

(post #72635, reply #4 of 27)

I put Simpson post brackets into my block when they were grouted and attached the posts to them.  10 years later, they show no sign of rot since they're an inch above any water.

(post #72635, reply #14 of 27)

What makes you say Allen Block won't hold 3'?  That's what they are engineered for, and unless it's real shifty soil I'd have a hard time believing it's going to move. 

Of course, you need to be smart, with gravel & drain tile behind if it starts to get tall, and use of the geogrid if the soil conditions and height warrant it.  I've seen lots taller than 3' that are perfectly stable.

(post #72635, reply #5 of 27)

I'm looking to use some sort of system I could do myself.  Some sort of finished concrete block type product.  Is there something out there that would work ?

Should I just consider poured concrete and face it with stone.  I am concerned with how it looks.


Thanks for the suggestions so far, are there any other ideas out there


thanks again

(post #72635, reply #6 of 27)

I called the Allen Block people to find out what they recommended for putting the posts into the blocks. I only wanted to go two layers with the block so that I wouldn't have a drop between my place and the neighbor. Guy next door went ahead and had the fence put up before I got to it, so I have the drop. Back to my point.

The Allen engineer (?) said, not to cement in the post into the blocks. He recommended that it be packed in with the crushed rock like the rest of the wall. I said, I said I would like to put the post into concrete below the wall and slide them on over top and pack them in with the aggregate. He liked that idea. That method would have added some extra cost for me as the 10' to 12' posts to accommodate a 6' fence would have cost a bit more. Not an issue for your shorter fence.

If the block companies were on the ball they would make special blocks and caps designed with fence posts in mind that can be put in the retaining walls where needed. It would be a solution for us and an opportunity for them to make more money.

If you go with a poured wall and are concerned about the appearance, you could go with an exposed aggregate look like driveways and walks sport

(post #72635, reply #7 of 27)

Should I just consider poured concrete and face it with stone I am concerned with how it looks.

There you go.  Cast-in-place is DIY friendly.  Stone facing, or texture the concrete inside the form.  Lots of texture choices available.  I once did 180 lin ft of colored concrete that looked like a board fence from 10' away.  Had a 4' tall rail fence sitting on it.  Pair or rebar pins inside each post, solid. 

Good footing and you have a solid foundation for your fence.  Here's an example:

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(post #72635, reply #8 of 27)

thanks again for the suggestions

it seems that in order to put the fence on top of the wall instead of next to it I will have to go with a poured wall with mounted post set in it, then place the wood post on the mounted posts some how.


Any other suggestions I will gladly take them



any pictures ?

(post #72635, reply #9 of 27)

 poured wall with mounted post set in it

Hope you're not thinking wood there.  Steel is better.  Good-sized pipe would let you go crazy building hollow outer posts.  Limited only by your imagination.

Owner sold the long-retaining-wall house when I agreed to build him a house like mine.  New owners are quite private (no pix).  Boards in the forms were vert. 

This's a piece of retaining wall here, 12' tall, textured concrete.  Didn't work out quite like I planned, but that's OK.  With form work, you generally plan negative spaces. 

PAHS Designer/Builder- Bury it!

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Retaining_Wall.jpg57.66 KB

(post #72635, reply #10 of 27)

I don't know if they are rated for exterior use, but there are those plastic spacer things generally used around support posts in basements. You attach these units in two pieces around the post, and you have a square shape to trim out with wood. I'm not sure I'm explaining it very well. Anyway, the company advertises in Fine Homebuilding.

If they are rated for exterior use, it seems like you could cement metal posts in the retaining wall and then do anything you want.

(post #72635, reply #11 of 27)

but there are those plastic spacer things generally used around support posts in basements.

I'm not familiar with them.  And I don't consider using posts in my "basements".  <G>  Clear spans are nicer.

With a pipe sticking out of the concrete it wouldn't take much to attach a hollow post, however-many sided.  On a snug fit, glue would suffice.  Unlike a basement, just slide it down from the top.  Ventilation at the bottom of the post is a detail best not ignored.

The fence on the retaining wall I poured was split rail.  Black locust, split by the HO.  Solid posts (small tree trunks) were driven down on 2 rebar pins.  Looked fine from the yard (where you didn't see the retaining wall) but peculiar from where you could see the concrete wall.  A split rail fence sitting on what looked like a board fence. 

Wasn't my place, or design...

PAHS Designer/Builder- Bury it!

PAHS works.  Bury it.

(post #72635, reply #12 of 27)

May have missed it, but how about CMU wall? Pour footing, wet set first row, then do it at your own pace? Drop in a pipe wher you want you posts the fill cells. Cap and face with stone, plaster etc.

Judo Chop!

__________________________ Judo Chop!

(post #72635, reply #13 of 27)

do you think a cmu wall will be able to withstand the movement of the fence do to wind, etc.  Do you think i would have to fill all the cell with concrete or just those in the immediate area of metal post.

I plan on doing a wood fence approx 4ft max, so I would have to mount the wood post on the metal post some how.

Any recommendations on what brand of cmu wall to use




(post #72635, reply #25 of 27)

Busy weekend...The CMU wall with chain link, wood fence, vinyl is quite common here. I have seen several ways as far as filling cells. Some are poured about 5-6 cells around the posts and the rest filled with gravel.
Some with all cells filled, some with gravel up to the 2nd to the top row then using bond beam blocks, rebar and bag mix the top( bond beam) "homeowner material saver version"

Either way a good footing and connection up through you posts is key.

Judo Chop!
__________________________ Judo Chop!

(post #72635, reply #15 of 27)

With all due respect to VATom, he's a complete concrete geek (and that's meant as a compliment!).  For those of us less interested in playing with forms and concrete the Allen Block is way more DYI-friendly and I love the results.

Is there anything in particular driving you to put the fence on top of the wall instead of behind it?  If behind you can plant the posts right behind the block; even bury the posts a foot if you use 8'.  Since the posts will be surrounded by gravel (you are planning to backfill with gravel, aren't you?) the propensity to rot is reduced. 

Will the fence have people leaning on it or will it just be a backdrop for plantings, etc?  If there is a chance that you'll have people leaning against it, the posts end up as levers with several hundred pounds (or more if it's a big party!) pushing against it - I wouldn't trust the blocks by themselves in that case (the same goes with the posts inside the block as behind it). Worth consulting the mfg. if that's the case.

It's a lower wall than yours, with no fence, but here's what I did:

Edited 7/2/2006 1:09 pm by wrudiger

AllenBlock.jpg52 KB

(post #72635, reply #16 of 27)

LOL   OK, the "geek" agrees that looks great.  But it's only on short walls I see any block advantage.  That's also the only place they don't look so obviously fake. 

Been a good many years since I priced Risi Stone and was shocked, never looked back.  Same client I did the 180' wall for did a small Risi himself.  Regretted not using concrete, which would have been cheaper and faster. 

A lot of my concrete attraction is price.  It's real easy to pour a substantial footing.  Mine are always under the fill.  After that, forming ain't exactly rocket science.


PAHS Designer/Builder- Bury it!

PAHS works.  Bury it.

(post #72635, reply #17 of 27)

I do have to agree with you - with growing height and length the stuff gets real pricy in a big hurry.

The other area I where I considered but did not use concrete was on a retaining wall on a downslope.  30 degree slope; 4' retained.  Had a long discussion with the engineer and we determined that the 8x8's burried 8' were far cheaper than the concrete (especially with the extra engineering required to support the weight of the concrete wall vs. a wood wall).

That's the wall at the top (with a 3' fence raising above it).  The rest of the walls are my favorite way to (re)use concrete.

Edited 7/2/2006 1:50 pm by wrudiger

retaining-wall.jpg66.79 KB

(post #72635, reply #18 of 27)

Found a nice flat place to call home didn't you?  <G>  Warms my heart. 

Even more when that wood retaining wall fails and you get to do it all over again.  Or maybe the next owner.  Lifespan costs are relevant.  Great predilection of mine to do it once and enjoy it forever.  I've replaced a few wood retaining walls (including where that 180' went), never here.  I'm also aware that wood decomposes at different rates in different places. 

You required to get new engineering for retaining walls? 

That drawing I posted came from a book of standard walls.  The one time I hired an engineer (for my first house with 15' of dirt behind the rear wall and a 200 ton roof) I took advantage of the opportunity to pick his brain about differences in footings, particularly the footing shown in that drawing.  Makes me, and my BI, comfortable with what I've done.

Sometimes placing concrete gets interesting.  I hate pumping, bought an ancient crane to avoid it.  I suppose you humped all those "stones" up there?  Looks good.  Often known as "urbanite".  Need a few hundred more tons?  I also occasionally get called to break up some.

PAHS Designer/Builder- Bury it!

PAHS works.  Bury it.

(post #72635, reply #19 of 27)

Engineering for retaining wall? - Yep, anything ofer 4', total height of footings plus exposed.  Goes through Public Works, not Building Dept.  They get kinda upset when something like this fails and dumps on the 4-lane at the bottom of the hill :-)

Given that I'm on a fairly plastic sandy clay, coupled with the fairly steep downslope, a poured wall would have had an interesting - to say the least - foundation: heafty piers & lots of rebar plus a pretty big apron thingie (not up on my foundation terms) as part of the footer sticking back into the hillside.  Whole different game when the wall's at the bottom of the hill, or has some sort reasonably wide flat place to plant itself.

Fortunately it's down, not up, to the terraces.  Gravity is my friend.  Yea, I figure I need another 10 ton or so of urbainte to finish off the terracing - just toss it on a train car and put my name on it - LOL.

(post #72635, reply #20 of 27)

Are you thinking something like this? Fence could be wood hung on steel posts. Eventually, we plan to have some kind of climber covering the chainlink. Finished grade on our side will be 12-18" higher than neighbor's. I don't like replacing fences.

This is Keystone Country Manor. The rep said it had never been done...gave me something to prove ;-)


Everything will be okay in the end.  If it's not okay, it's not the end. 


Everything will be okay in the end.  If it's not okay, it's not the end. 

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(post #72635, reply #21 of 27)

Yes, that is what I am Looking to do.  Only I want it to be a wooden fence.  I suppose I will use metal post and cover them with wood.  How and how far did you sink the post in the block.  Any problems encountered ?

any other in will be a great help.  All the suppliers around here said it cant done as well.


(post #72635, reply #22 of 27)

Hiya Nash,

Posts are actually sunk in concrete below retaining wall. As I remember the posts are about 9' tall. 3' below grade, 3' in wall, 3' chain link. I trimmed the posts after wall was done. One of the rep's concerns was wind loading. There could be significant side force if the wall were supporting the posts.

This particular block has holes in some some of the "stones". I mocked up a section in the driveway to determine post spacing to take advantage of the holes. Even with careful layout I ended up drilling a series of holes in a lot of the blocks and chipping out a cavity with an air chisel. Got pretty good at it! If you look closely the posts either skewer a block or are near the end of one.

Progression was like this; dig trench, set posts, compact 3/4 crushed stone in trench, set blocks, set caps, trim posts and install fence. I could make about 15' a day by the time I finished. Wore out many pairs of gloves, and had  my neighbors wondering about my sanity :-).

Need more info / pics? Just ask.


Everything will be okay in the end.  If it's not okay, it's not the end. 

Edited 7/3/2006 10:40 am ET by PeterJ


Everything will be okay in the end.  If it's not okay, it's not the end. 

(post #72635, reply #24 of 27)

Musta been real fun lifting the big blocks up & over the posts settin 6' in the air! Don't know about yours, but my biggest blocks are 83#.  Ouch!  Looks great, though.

(post #72635, reply #26 of 27)

Oh yeah, it was big fun ;)  By the time I finished, I had a pretty good system going, a tan and bigger biceps. My DW helped me exactly once, which she felt was plenty. But I had a vision.............ahh, you know the rest! 



Everything will be okay in the end.  If it's not okay, it's not the end. 


Everything will be okay in the end.  If it's not okay, it's not the end. 

(post #72635, reply #27 of 27)

Im looking to put fence on top of wall because I think it will look better and I have A small yard, every inch counts.  I also should add that I live on a hill and the 3ft height difference between me and my nieghbor

(post #72635, reply #23 of 27)

Well, wood-to-metal-posts is actually easy, you just have to find the right fence supplier.  They make stock galvanized parts to go around both 1-5/8 & 2-5/8" fence posts, which can then be screwed or bolted to wooden fence parts.

It's my preference, in the much we call soil around here (layers of riverbottom--so altenating sand with mud or sand with clay, or clay with mud), is to use galvanized posts to support wooden privacy fences.  Keeping wooden fence posts out of contact with our perennially damp soils is a net good.

Now, of your wall, I'd be strongly tempted to split-face cmu if the construction is to be DIY.  I'd spend some dollars on engineering to go with that, over 2' high, though.  Why?  Because everything I've been taught about soils engineering is that all faliures are bad.  Also, that the mechanics of soil just love cube functions (so, the difference between 2' tall & 3' tall is not that 3' is a third more force, but 9x).

So, what you might need, is a nice deep foundation, with a nice deep footing behind it (making a laid-over "L" shape).  Than, upon that would go the block wall.  With a good foundation, comes the base for the fence posts.

Occupational hazard of my occupation not being around (sorry Bubba)
I may not be able to help you Occupational hazard of my occupation not being around (sorry Bubba)