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Installing an 8' tall curved wood fence on concrete patio.

Installing an 8' tall curved wood fence on concrete patio.

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  #1  
Old 09-16-19, 01:27 PM
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Installing an 8' tall curved wood fence on concrete patio.

I'm going to install (or have someone else do it, if I can find someone) an 8' high wood privacy fence, about 12.5' long on a semi circle side of a concrete patio. The fence will be curved. Have decided cedar is the way to go, with either pt pine 4x4 posts or metal posts. How many rails is recommended for an approx. 8' high fence? Had someone give a bid today, and he said he was going to go 8" deep for the posts. Read the standard is to go at least 1/3 of the length of the post deep.......if drilling into a concrete patio, the typical depth would still be 1/3 of the length, or is there some reason the contractor thought 8" would be sufficient? What is the best method for drilling a post hole into concrete, and then about 3' into the ground?
 
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  #2  
Old 09-16-19, 01:58 PM
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I think he's relying on the concrete to provide salability and drainage. I would not go that route. I think any freezing of water will heave the post and may buckle the concrete. But I'm not expert and I would wait for others to chime in.
 
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Old 09-16-19, 02:17 PM
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I'd think a few good gusts of wind might send the whole fence over, with only 8" deep posts. 8' high cedar board over board fence is a lot of weight...still, trying to give the guy the benefit of a doubt....
 
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Old 09-16-19, 04:10 PM
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I doubt the contractor will be only going 8" deep especially after having cut holes in the concrete. After all, cutting the concrete is the hard part. Augering or post hole digging into the ground underneath is the easy part of the job.
 
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Old 09-17-19, 07:31 AM
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Is the semi circle actually half a circle re: a 12.5' diameter?
If yes then the contractor is probably relying on the circle shape to provide strength and rigidity.
Or is it 12.5' of curved fence and not an actual semi circle, a gentle curve will have a lot less strength than a semi circle.

Also how far from the outside edge of the concrete pad will the post be.
If too close then cracking of the concrete can happen.

Another thing to consider is the inside arc protected from the prevailing winds?

How thick is the concrete and is it rebarred?

I think the contractor is using the holes just to anchor the fence and the fence structure itself is providing all the strength.

It is possible that the contractors idea would work.

If you are far enough in from the edge of the concrete pad and it is fairly thick and a semi circle then the way I would build it is to cut the hole and remove the soil a few inches from under the concrete. This will ensure that the posts cannot pull up out of the concrete. Also bevel the top of the hole so they cannot drop down. Basically you now have a concrete plug that is solid in the hole. His 8"or so should be OK for depth.
Since trying to get the posts to stay properly vertical with only that mush in the ground I would build the fence in place but then concrete the post in later.

You did not say how far apart your post will be and that is important when you figure out how many rails you need. Also how you are going to achieve the curve.
 
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Old 09-18-19, 10:34 AM
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Manden,

Thanks for the detailed reply. It is not truly a half circle with a 12.5' diameter. The depth of the patio cement goes from 8" to 4" from one side of the semi circle to the other. There is no wind barrier so the fence would get the full force of any winds that happen....and it does get windy in Georgia. The posts would be about 3" to 4" from the edge of the concrete. There almost certainly isn't any rebar in the patio concrete, and the concrete is about sixty years old and not in pristine condition. One contractor said he would use four poles the other five - inclusive of the 2 end poles. The four poles would be about 4' apart the five pole would be about 2' apart. I've had two contractors both state the 8" depth would be sufficient. I have a feeling, neither one really thought the situation through, and this may be a new scenario for them.....we get gusty winds, which could be a problem, I think.....Also, one contractor wants to use cedar posts, the other wants to use treated pine....from what i've read, treated pine is the better choice, as cedar tends to rot quicker when in the ground....

Just to add, I asked the contractor today whether he was confident 8" would be enough for the poles, and he stated that the existing concrete would provide the needed strength.
When I told him that the rule of thumb seems to be 1/3 the length of the pole should be in the ground, he said that that was because the pole would normally be going into dirt which doesn't have the strength of concrete......but presumeably, normally a pole would go into freshly poured concrete, not dirt........
 

Last edited by Tonesg; 09-18-19 at 11:20 AM. Reason: grammer
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Old 09-18-19, 10:55 AM
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the pole would normally be going into dirt which doesn't have the strength of concrete
The concrete patio is not a structural component for the fence, basically you are just cutting a clearance hole through the patio so the fence has to be self supporting, meaning the 1/3 (min) would apply!
 
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Old 09-18-19, 11:15 AM
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"Is the semi circle actually half a circle re: a 12.5' diameter?"

This slipped by me. It's a curved edge, not a half circle of a 12.5' diameter circle......Not sure what the circle diameter would be if the curved edge was followed, but it would be a lot larger than a 12.5' diameter circle. The curve at it's center - around 6' - is about 2' from a straight line.
 
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Old 09-18-19, 11:18 AM
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"....... the 1/3 (min) would apply!"

That's consistent with everything i've read....don't understand why these contractors seem to want to cut corners.
 
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Old 09-18-19, 04:28 PM
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I would be afraid that putting holes that large, that close to the edge could cause the outer chunk of concrete to break off. If it were mine I would probably auger my post holes just off the edge of the concrete so the posts could be located as close to the patio as possible.
 
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Old 09-19-19, 07:23 AM
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I agree with Pilot Dane.

If your screen breaks up the cement then repairing it will be a royal pain in the you know what.

Also since your curvature is small the screen will not have much if any stand up strength of it's own.
So it must be built the same way you would build a straight fence.
 
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Old 09-19-19, 02:02 PM
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I found a concrete contractor who is willing to drill through the concrete and into the soil deep enough to get 1/3 of the post into the ground. If he drills an 8" diameter hole 4" in from the edge of the patio, at least 3' into the ground below the concrete, it seems like that might be sufficient to hold the posts and fence in place......
 
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