Bolt-down fence-post anchors

[porkchop1]

I am looking to put a fence up across a concreted area in my back garden but I am unsure of how high a fence these post anchors can support. If I use 4"x4" anchors will they support a 5ft fence? And how long do the bolts need to be? How high a fence can 3"x3" anchors support? Is there a general rule to follow for this kind of thing?

Also, is there any reason to not use these fence anchors on block paving? Will it pull the blocks up if it gets windy?

I have the skill to be able to construct a fence but not the experience to know if it will last! Any advice will be hugely appreciated. Thank you in advance.

 

[Thermo]

dont even consider it on block paving. block paviors are held down by gravity and locked in place by each other and the jointing sand. high wind loading could seriously disturb them so they are not a good prospect for bolting down to. Youd be better off removing some of the blocks, digging normal fence post holes and then replacing the blocks back, and cutting around the posts. It will be stronger and look a lot neater.

 

[porkchop1]

Thanks for the advice, I had kind of guessed that about the block paving. Any advice on the other questions I had?

 

[porkchop1]

Anyone?

 

[freddiemercurystwin]

If you type in the size of posts and height etc it'll tell you which parts to use: http://www.metpost.co.uk/mp_fenc_calc.html

To be honest it looks like both your questions were answered, Thermo suggested you dug holes and embedded the posts instead of going down the lazyboy route!

 

[Thermo]

thought i did!

 

[porkchop1]

Thanks for the link, just what I was looking for.

I really appreciate your help guys, but I think I may have caused some confusion. I need to build a fence across concrete, and a small section of block paving. My main question was about the fencing on the concrete.

 

[Thermo]

in that case yes you could use rawl bolt anchors, minimum 100mm long. best to use some oversize washers on the heads of the bolts as the plates can flimsey be quite flimsey
In my humble opinion the bolt down plates are still not brilliant and you will still get movement in the fence. Sometimes they ae the omly option. i went to one job recently where one had been down a year and the metal shoe had sheared off of the plate in the wind. We cut a neat hole with a still saw and carful use of a jack hammer. then dug the hole using a pointing trowel and hand. Looked like it had been cast in the concrete when we had finished and solid as a rock.

 

[JohnD]

You can get a post socket with a great piece of barley-sugar-twist rebar welded to the end. You could cast that in, or drill an interference-fit hole in the concrete. It looks like it would hold better than the bolts.