Some people call them wood fence toppers. I prefer calling it a wood fence extension atop a hollow concrete block wall as is the case in this case. Solid concrete walls are a little different, that will be a different article.
The lazy, cheap, weak and inexperienced way is to lay a flat member like a 2×4 or a 4×4 down horizontally on the cap row and attach to the cap row only with either Hilti concrete nails or more often I see TapCon brand blue 1/4″, maybe 5/16″ or 3/8″ concrete screws. This is wrong because it’s only as strong as the mortar holding the cap row onto the wall below. It’s also wrong because the flat wood member lying upon and attached to the cap row will develop rot and attract termites, because it’s outside. And it’s wrong because it’s weak with no leverage strength built into it. Sure it’s how you build walls for a house, but that’s different because house walls have a waterproof skin to seal out moisture, rot and termites. It’s how you build walls for a house, but there are no other walls or a roof to attach to for strength, so it’s weak.
Just like a “regular” wood fence, you need solid vertical wood posts to build from and upon. Carefully core drill holes in the concrete or brick cap row, right where you need them. This is determined by your post spacing, heavy duty “L” bracket position that will be fastened to each post, as well as positioned over a hollow vertical cavity in the wall-to pour fresh mixed concrete into, all the way to the top! Yep. Dropping a stick or two of 3/8″, maybe even 1/2″ rebar (depending on the specifics of the situation of course) into the cavity just before the concrete pour certainly will make it even stronger and better. And longer lasting of course, which is what we all want, right?
After your layout is all done, cap cores are drilled out, fill ’em up! Oh yeah, have your 1/2″ threaded rod pieces all ready to go, each with a washer and hex nut to keep them from sinking into that fresh concrete. Concrete should be a little wet for this, but not too much. Position your “L” brackets where they’re going to be, drop the threaded rod into the fresh concrete and let the concrete do its job (permanently grabbing that entire cavity of the wall and permanently grabbing the threaded rod). Of course there are other details like alignment, specific post spacing, threaded rod length, type of “L” bracket, etc. You have to keep an eye on every cavity after pouring and setting the hardware for concrete seepage and corresponding dropping from the top, do this as long as it takes, and top them off as necessary for an even and flat result with the top of the cap. Figure it out or call, text or email me to have me build it right. THIS article is just to point out the primary basic method to attach to the top of the wall correctly and securely.
Every situation is different. Therefore as the designer and builder it is necessary to design and build for the specific situation in each and every instance. Right? Right. The photo below shows it all done.
If you’re a DIY’er or a fellow builder researching how to build a wood fence extension on top of a hollow concrete block wall: You’re welcome! If you need this done for your property or estate just call, text or email me. 310-717-2000 is my cell.
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