Fence post depth

[Cursitor Doom]

Hi all,

How deep below ground level should a post hole be for a close-boarded fence that's 5.5' high? The post in question is 100mm square in section if that makes any difference.

cheers, cd.

[polygonum]

What makes a huge difference is the nature of the ground.

[charles]

I suspect it depends on what the ground is made of, but I'd think 2' at a minimum. If you have a wide hole and add concrete you might get away with less.

[fred]

And where it is located, on Uist (windyland), there are no close boarded fences at all and 50% cover windbreak fences of 1m high need at least 1m in the ground (plus stays).

Assuming shandy land, I'd be suggesting 500-750mm.

[Dave Liquorice]

Rule of thumb is 1/3 total length in ground so 5'6" above indicates

2'3" in. Giving, more or less, the normal fence post length of 8' (2.4 m).

[Cursitor Doom]

The soil and subsoil is pretty unremarkable. But we do get a lot of gales here from Oct through to the end of March. I plan to make the hole about

2cm wider than the post all the way around and tip Postcrete into the gap.

[Roger Mills]

Shouldn't that be 2'9" in the ground?

[newshound]

Also a long fence will need better support than (say) the centre post of a two panel fence where the outer posts are supported by fencing at 90 degrees. If it within about three of "heights" of higher objects (trees, houses) it needs less support because the wind speed at ground level will be reduced by the "boundary layer effect".

But the 1/3 rule of thumb mentioned elsewhere is a good start.

[Cursitor Doom]

I make it 22" by the one-third rule. Sounds about right, I reckon.

[polygonum]

That could be right if you only want 44" (3' 8") above ground. You are calculating one third of above ground height- not one third of TOTAL post length.

[harryagain]

The main factor is "how windy is it?" Also are there any corners that help support it. And can you fit any stays/diagonal props?

Metal fence spikes are a better solution. Reduces rot. And the post needn't go in as deep as the concrete if you use concrete.

If the ground is soft, you need a bigger "ball" of oncrete. You can eke out the concrete with bits of rubble/bricks/etc

[Dave Liquorice]

indicates

Er, yes, I think you can see what I did wrong...

[Dave Liquorice]

Aye, no fence panels up here. First decent blow would have them ripped to shreds and scattered across the fells...

If you have nice ground without any stones that make driving in a spike a right PITA. Driving in plumb even in good ground is not easy. Extending the life of the post is good but only works if the base of the post/spike socket is kept clear of soil vegitation build up etc.

You don't want the post in a closed base pocket of concrete, holds water, increases rate of rot just above the surafce line.

Balls will rotate in the ground and concrete is a PITA to shift/break up when (not if) the post rots and needs replacing. Soft ground is easy to dig a decent depth (1/3 rule...) hole and put the post in firmly ramming back in in as much spoil as possible. Keep the hole a small as possible to avoid disturbing the ground, maybe aim for 1" clearance all round and have a 6' 1" dia iron bar to do the ramming, that will have a bit of weight use it...

[Andrew Gabriel]

"Balls" swivel in high winds, as my neighbour discovered (but strangely would never swivel back into the right position, regardless of force applied). Aim for a "cube" of concrete.

[harryagain]

To put in fence spikes straight, you need to make a pilot hole in the ground with an iron bar. The spike will follow the hole as you hammer it in.

[charles]

Simply dig? When the ground is fully of flints that takes a few hours.

[Vir Campestris]

Yes, they rust instead.

I have a number of rusty spikes about the garden, and a few perfectly sound concrete spurs where the fence has rotted off completely.

Replacing the ones on the spurs will need a spanner, and no digging at all. Next door has just had her fence replaced with 8ft concrete posts - they should be good till I'm long dead.

Andy

[Andrew Gabriel]

I used metal spikes for a fence I replaced almost 30 years ago, and they're all still fine. The make was Fensock, which I don't think still exists and was better quality than the metapost products I see in the sheds today. Spikes didn't need to be dead straight in the ground - you could compensate to some extent when clamping the post bottom onto the metal sockets.

Depends a lot on the quality - in particular how well the internal rebar is protected from the weather. Can spall and fall to bits quite quickly if poor quality - has happened to a fence I walk past which is no more than 15 years old.

If I was having such a fence erected today, I would specify concrete repair posts concreted into the ground, with timber posts bolted to them and just clear of the ground. People often end up with this after original posts rot at the ground surface, but once it's been done, the post and support seem to last forever. I have seen a concrete spur post snap, but that was where it effectively had a

10' fence on it due to ground level changes either side, and there was a howling gale which did lots of other damage too.

[Cursitor Doom]

I said Postcrete, not concrete. Different thing altogether.

[Dave Liquorice]

bottom.

Such a big hole disturbs the ground too much. It is far better to have the post buried to the 1/3 rule in a hole that is as snug as possible and ram the spoil back in. You do not need concrete. If you end up with a ballish shape it'll just rotate. Any "weight at the bottom", unless it is very considerable, is not going to have much effect just below the pivot point, ie surface level ish.

Quite and the ground is now really fupped up for putting anything back into.

Having done battle with several lumps of concrete about 12" square and 18" long "lift it out" just ain't going to happen. Something that size is >>30 kg. I can pick up and carry 25 kg bags of cement/plaster etc but that's when I can get hold of them properly and not below the surface you are stood on.