As plans for garden destruction accelerate at an alarming pace, some of the garage base will need to remain to prevent fence going all fally-over in a wind.

The concrete is about 2 inch and the gravelly base depth is about the same

I’d like 6 inch, my electrician (don’t ask) friend says 12″.

Place your bets now!

What are you asking? Are you gonna drop the posts into that wee earthy bit and screw through side to the concrete? Or use brackets on top?.

If it’s only 2″ thick, I’d break up a big enough area to properly sink and postcrete each post, 2′ deep, use the broken up concrete bits to batter down side of post once in hole, hold it steady, then postcrete.

My bad. Posts to remain in place.

The badly phrased question is how much of the the concrete base do I need to leave (the horizontal distance from the fence posts) so the fence remains secure?

None. The post bases would be completely independent of the slab.

Are the posts bolted to the slab?
If so then probably most of it!
Your asking a 5 ft high fence to be held up by 6” wide 2” deep piece of concrete!
Surely the law of physics will dictate 6” can’t hold up 5ft

None. The post bases would be completely independent of the slab.

Photo shows met posts bolted to concrete slab.

I’d be more inclined to listen to your electrician.

None. The post bases would be completely independent of the slab.

No they look like flush mounted metal brackets that bolt to the surface

I would remove all the current base and concrete in a new post holder spike thing, otherwise I think you are going to have to leave more than you think for it to be stable.

Alot more than 12inches.

Unless the slab extends beneath the fence and out the otherside that slab is providing a counterweight to the cantilever.put in some concrete grandads or whatever they are called?

Is the fence wrapped around a body? If so, 6 feet deep and the top foot concrete…

No they look like flush mounted metal brackets that bolt to the surface

Yeah, exactly that, a square, four-sided steel box with a piddly little flange around the bottom with four bolts into the concrete. I wouldn’t trust that to stay up if a dog peed on it, let alone a strong wind! I’d definitely want the shed to stay there, it’s all that’s holding the fence upright.

Cheers folks. Think I’ll remove everything then and stick in new concrete posts.. Yay, more work.

Just smash up the concrete, dig a hole and replace the bolted base with a bolt on concrete in version. Then put in a bag of postcrete.

It looks fairly sheltered and the fence is hit and miss/double palisade which reduces wind loading so doesn’t look like it warrants the effort of full concrete posts.

No need to remove it all, you can just fit concrete spurs in situ and bolt through to the existing post. I’ve replaced the bottom 2′ of 40 odd fence posts using this method.

[url=https://flic.kr/p/wiM3iB]Concrete Spur[/url] by Ben Freeman, on Flickr