wooden field gates - what size posts for what size gates?

Have some farm gates to hang but this time timber ones off timber posts.
Is there a rule of thumb for how big cross section of posts are and how long (i.e. how much to bury) for best results? oh and what to bury in? concrete? or just backfill? & how deep?
Gates are to be one @ 11 ft, 2@13ft (or maybe one @14ft & one @12ft to meet in middle
Posts available are 5" 6" 7" 8" square in 7, 8 or 10ft lengths.
TIA
Jim K
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On 22/04/2014 17:14, JimK wrote:

Recommendations from a gate manufacturer here:
http://www.fencingsupplies.co.uk/?page_idD6
I would go for the biggest you can afford, as deep as you can bore the hole, backfilled with well tamped gravel. Alternatively, as I did for a pair of 6ft high x 10ft wide gates, an inverted U of welded RSJ, set in concrete across the base, with hinge pins welded to the uprights and those built into brick piers on either side
Colin Bignell
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On 22/04/2014 17:36, Nightjar wrote:

Typically farmers will not concrete in posts as the wood rots ... better to dig hole at least equiv to 1/3 of post length ... have stones or gravel on bottom, and backfill hole with stones & gravel packing down well every 150mm
I would use 8" posts if you are going for 12' gates ...
--
UK SelfBuild: http://uk.groups.yahoo.com/group/UK_Selfbuild/

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"Nightjar" wrote in message

Colin, that's pretty well exactly how I did my gate off the main road. 10x6 RSJ buried in 3 foot deep concreted trench across drive with 10x6 uprights in centre of pillars, again like you having hinge pivots welded to the rsj, then quite a solid pillar (I think 3 bricks per side) with the void filled with concrete. Will give someone a surprise if they run into it, even in a tank :) We are on fairly soft clay here and posts and pillars have a habit of moving, so I wanted the whole structure to be integrated ! This was for a 12 foot gate that is electrically operated off one pillar, so a fair bit of torque applied.
Andrew
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On 22/04/2014 21:42, Andrew Mawson wrote:

I just didn't want to be faffing about with replacing gate posts once I reached my dotage :-)
Colin Bignell
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On Tue, 22 Apr 2014 09:14:57 -0700 (PDT), JimK wrote:

I don't follow the maths there at all, but I'm sure you understand it. B-)

How high are the gates? What does that give as post above ground level? As a rough rule of thumb you then need half that in the ground, ie. 1/3 of total post length in the ground. I'd not bother with concrete(*) just make the hole as snug as possiblle and hard pack/ram stones and earth back in around the post. You might get away with less but not a lot less. Also arrange things such that the gate is supported at the non-hinge end most of the time, either by the latch or having the stile(?) rest on something. This lessens the torque load on the popst/hinges and is good for the gate, it won't "drop".
(*) You just end up with a 25 to 50 kg solid lump buried in the ground that will be a right PITA when the post rots and needs to be replaced. Note: "when" not "if".
--
Cheers
Dave.
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I'd go for 7" and 8'.
I use tamped rubble backfill as I don't expect more than 10 years life out of modern preservatives.
--
Tim Lamb

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