Howdy all.
I want to put up a wood fence, mounted on top of an existing poured concrete wall that's about 2' tall. My question is about how to connect the wooden posts to the concrete securely.

I was thinking of drilling into the concrete, setting maybe 3/4" threaded bolts (using bolt-setting cement), then mounting the wood posts to the bolts by drilling up through the center, and a large hole perpendicular for the nut and washer. This is akin to how staircase bannisters are mounted. Do you guys think that'd be secure enough for a 5' tall fence?

Should I use some kind of special steel brackets as extra support? Is there a standard method for doing this?

One other alternative would be to set the main wood posts in the ground, in concrete as a normal fence is built, then simply connect the wood fence starting on top of the concrete. I didn't want to do this because then I lose the straight wall, (having wood posts sticking out) which just means more weeds and stuff along that wall. I also feel like it'd promote faster rot of the wood posts, in that cramped space where they're butted against the concrete wall. That'd be moist probably all year.

Thanks for any suggestions!

- james

... local hardware stores for a line of products made by Simpson referred to as their line of Strongties?
http://www.strongtie.com/

Is the fence going to be a solid wood fence 5' above the concrete? If so, It will have substantial wind loads. Drilling big enough holes for 3/4'' bolts in concrete will be a task. I am not even sure the bottom of the post with the 2 holes in it will hold the load. Have you considered running a 2 x 4 plate of pressured treated wood. Fasten the posts to the 2 x 4 with large lag screws, and then set the plate on the wall and screw it down with Tapcons, making up for their smalls size with numbers. With a good bit and a light hammer drill, you can zip right along drilling Tapcon holes 2'' deep. Or you could rent a Hilti gun and shoot anchors for the plate if the fence is going to be very long.

Yes, my main concern was the wind load. Reconsidering my first idea, I'm afraid the posts would split at the bottom and the whole thing would blow over.

I like the idea of running a 2x4 strip along the bottom. Thanks! Then I can use some strongtie supports (probably flat-bar style) as extra anchoring for the posts. I'm lucky that I have already collected both a hammer-drill and a powder nailer, so between the two I bet I can get this fairly secure.

Labman, those Tapcon screws you're talking about, are they the blue screws that say they'll screw right into concrete? If so, what's the trick with those? I tried some a while back and they kept breaking on me when I'd get them about halfway into the pilot hole! Frustrating. Maybe I was driving them too fast or something.

Anyway, thanks again and I'll chat again soon!

- james

Yes, the Tapcons are the blue screws. I have had good luck with them once I get the holes drilled. Perhaps the old drills I use, make a slightly larger hole. Could try the old carpenter's trick of soap on the threads.