Attaching Fencing to Caps--Right or Wrong?

Fence Systems, Wall Failures
By Doug Blackburn
Dec 4, 2008 - 7:16:44 AM

Dear Joe,  

I'm remodeling my back yard and want to enclose an RV parking area. There is a 3-4 foot Allan block retaining wall on the property line. It is filled with cement and capped off with a convex cement top. What is the best way to attach a vinyl fence to the top of the Allan block wall? The Allan block wall is on my side of the property, and the neighbor's side is the up hill side. I already asked the neighbors (my property spans two lots) if I could put the posts for the vinyl fence on their side so the fence would be flush with the ground and the wall. One said yes and one said no. If I put the post on my side there will be a gap between the vinyl fence and the retaining wall, and there will likely be visible posts with the bottom of the vinyl fence starting level with the top of the Allan block wall. I've searched the internet for answers and pictures and have not found any yet. Any answers?  

Sincerely,   DC


Dear DC,  

Thanks for the question.  Generally, you do not want to attach a fence to the top of the caps in a retaining wall.  Those caps usually weigh about 15 lbs each and just can’t take the forces applied to them without turning over, cracking or completely breaking off. 

Because your wall and caps are concrete filled (and because of your property line situation) it MAY be okay to attach the fence posts there.  People have had success doing this, however; more often than not, the fences (and caps) have failed.  If you decide to proceed with this method, make sure that you core into the blocks (not just the caps).  Don’t attach the fence directly to the cap – that won’t work. 

It would be really helpful if you sent us some pictures of the area.   Also, please send us photos showing us how you addressed it.  Meanwhile, I’ve attached some of photos and a link to one of our videos that addresses fencing of walls.  Let us know if you need anything else and we’ll look for those pics soon.

Best regards,

Remember, if you have a little room behind the wall, one of the best solutions is the Sleeve-It system.  For more info about Sleeve-It, see