Fence post attach to retaining wall


  #1  
Old 05-22-23, 08:51 AM
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Fence post attach to retaining wall

Hi Guys,

I want to update the fence on the back of my house. It looks like the existing fence posts are attached to a retaining wall with 2 bolt in the back of the retaining wall. My house yard is on big slab part of the retaining wall. There appears to be some 2x4 pieces that brace it at the top as well. I cant tell if the post is actually cemented into the ground.

The posts are very old and rotten and need to be replaced. Should I be digging a hole for cement the posts to the ground in addition to bolting them to the retaining wall, or is the retaining wall bolts enough with the 2x4 bracing enough? How deep of a hole if I use cement? These posts are approximately 9.5fet from ground level to top.

Pictures are view from neighbors side, but its fence so I can't dig under the post to see if its actually in the ground. But regardless, whats the best method for installation of the posts?


 

Last edited by gorth97; 05-22-23 at 09:15 AM.
  #2  
Old 05-22-23, 09:29 AM
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Here is the view from my side of the yard.


 
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Old 05-22-23, 09:53 AM
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Looking at the pix, it appears to me those are 4x4s w/a groove cut in it to allow the horizontal boards to slide down and be anchored. Is this accurate? The only securing I can see in the photos looks like 2 bolts anchoring the 4x4 to the wall (top and bottom). If so that seems like a lot of load for those 2 small bolts to hold, not vertical but horizontal (wind loading).

Rule of thumb is 1/3 in the ground 2/3 exposed, though I've gotten away easily with 1/4 and 3/4. My soil is heavy clay/rock so that might be the reason. As an example, I'm currently replacing a 23+ years old fence that has 2' buried 4x6 holding a 18" wood retaining wall w/6' pickets above. I'd be comfortable with 2' in the ground and what looks like 2' bolted into your wall. That's assuming the wall is filled and not hollow.

You will have difficulty redoing the posts holes next to a cmu wall w/a footing. Based upon my limited experience I don't envy the job.
 
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Old 05-22-23, 10:12 AM
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Yes the 4x4 are grooved. The boards slide down but are not anchored. I can easily slide them back up. We plan to changing the design so its not grooved and will just put horizontal boards directly against the 4x4, screwed in.

So what you're saying is digging a hole right next to the wall will be tough?
 
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Old 05-22-23, 01:07 PM
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Yes if that wall has a proper footing. The footing will extend out from the vertical plane of the wall a certain distance (google block wall footing) and look at pictures. I know you said you "can't" but the best thing to do is excavate down around one of the posts and see what the previous installer did. They might have attached it only with the bolts, or maybe you're lucky and they attached some type of metal support bracket when they put in the wall (which hopefully would still be usable) in which case you can decide.... "It lasted this long, maybe I'll duplicate it".

I just think a fence bolted to the wall (with two small bolts?) would be a rather weak connection/support....but hey maybe they did something I'm not seeing/thinking of.
 
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Old 05-22-23, 02:33 PM
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Thanks! Just walked over to neighbors and inspected two posts. They are just burried into the ground by about 4" and no concrete. They are anchored by those two bolts. It does feel pretty strong probably because its held onto the wall.

I think we will continue with that path and maybe put these plates on for extreme support?

https://www.homedepot.com/p/Simpson-...PT7Z/100375066
 
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Old 05-22-23, 03:22 PM
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I'm not a pro and maybe one of them will chime in, but yeah since it's lasted this long.......

I usually over engineer stuff to make up for my lack of technical knowledge so take the following with a grain of salt. If it were me, I'd rest the new 4X4 either on a very small exposed concrete footing before attaching it to the wall. You might be able to dig down to the footer and fill up a small column of concrete to rest the new 4x4 on. The intent being to spread some the vertical load on the bottom of the post out more than a wooden 4x4 attached to a wall would simply provide. Once I was comfortable some of the vertical load is being somewhat supported, then I would use your brackets (I'd use at least 3) to secure it to the wall. The most important thing to focus on is the connection of the bolts to the wall as that is going to be your weak point (and your main support point). Make sure that connection is the best you can accomplish in that wall.

Also, you won't be able to use the approved fasteners (through bolts) for attachment to the wall but at least use the approved nails ((5) 0.148" x 3" ) to secure the post to the bracket.

Just noticed, the caveat on using those brackets is that if your new post is not slightly larger than the depth of the bracket (3.5") you won't get the needed compression to hold the post against the block wall (remember the wood will shrink over time). The original installation used those bolts and/or nuts to compress the wood to secure it to the wall (and probably required tightening over the years). If you use the brackets, you might need to shim between the bracket and the post to provide the needed compression. If this is the case, I'd use some 1/4" flat bar the height of the bracket as a shim.

Good luck come back and show us the results!
 
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Old 05-22-23, 08:56 PM
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Do you know what kind of anchor to the wall would be good ?

Which anchor would you use if you were going to attach the wood directly to the concrete wall?
And which achor would you use to attach the bracket to the wall?

Would those blue tapcons work okay? 3" long for the bracket, and 6" long for the posts?
 

Last edited by gorth97; 05-22-23 at 09:06 PM.
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Old 05-23-23, 08:19 AM
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To be honest, without knowing the strength of those blocks and my minimal experience with fastening to CMUs I wouldn't feel comfortable recommending a specific fastener. You might start a new thread over on the masonry/cinder block forum to hopefully get the attention of a pro that might recommend an attachment fastener for your wall/application.

RE: Tapcons, the only positive experience I've had with these is installing them into finished (i.e.harder) concrete. CMU blocks (to me) don't have a lot of sheer strength (comparatively) and the relatively small diameter of them I would think would lead to tear out in your application. Your fence will have a lot of lateral load on it just being fastened to a wall. Sorry to beg off on this but a pro/someone whos dealt with that type of wall system more extensively would be a better information source.
 
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Old 05-28-23, 10:40 AM
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Looking great. We used the brackets putting redhead anchor 3/8 3 sleeves and Titen HD 3/8 6 screws directly on the wood. Feels strong.

cmu blocks were not hollow. Two brackets and one direct screw per post. So its 5 total anchors per post.

The posts used to have two 6 screws similar to the Titen HDs.



K

A
 

Last edited by gorth97; 05-28-23 at 11:00 AM.
  #11  
Old 05-28-23, 02:46 PM
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Looks Great! Really upclasses your pool area. I really like the 2 different widths effects of your horizontal boards.

Saw you got the answer you needed on the other forum. The pros on here are pretty impressive with their knowledge.
 
 

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