An overview of the BS 1722 standard requirements for the installation of fencing.
The Short Answer:
Typically 600mm for fences less than 1.5m high and to a depth of 750mm for other fence heights.
The Long Answer:
600mm is a good general rule of thumb but there are a few problems with it. The standards covering fences are set out in BS 1722 and they vary slightly depending on what type of fence you are installing. The materials themselves can also have an impact on post hole depth as certain types of concrete post have ground level predefined on them. In the image above you can see a little nib in the slot on the side of the concrete posts. That's manufactured at about 500mm from the end of the post and fixes ground level at that height.
What do the standards actually say?
Specification for chain link fences. BS 1722-1
Straining posts (end posts) shall be set 0.6 m in the ground for fences up to and including 1.4 m high and 0.75 m for fences over 1.4 m high. Holes for straining posts set in concrete shall be not less than 0.45 m × 0.45 m, or, if round, 0.3 m in diameter.
Intermediate posts shall be set or driven 0.6 m into the ground for fences up to and including 1.4 m high, and 0.75 m for fences over 1.4 m high. Square holes for intermediate posts set in concrete, for fences up to and including 1.4 m high, shall allow at least 75 mm of concrete all round the post. Round holes shall be at least 0.3 m in diameter, and posts shall be set in the centre of the hole. Holes for intermediate posts for fences over 1.4 m high shall be at least 300 mm × 300 mm. Round holes for intermediate posts for fences over 1.4 m high shall be at least 0.3 m in diameter.
Specification for Close-boarded Fences and Wooden Palisade Fences. BS 1722-5, BS 1722-6
Posts shall normally be set vertically in the ground to a depth of 0.6 m for fences less than 1.5 m high, and to a depth of 0.75 m for other fence heights. Holes for posts set in concrete shall be not less than 0.3 m × 0.3 m in plan, or, if round, as produced by an auger, not less than 0.3 m in diameter.
Wooden Post and Rail. BS 1722-7
Main posts shall be set vertically in the ground to a depth of 0.6 m for fences 1.1 m high, and to a depth of 0.7 m for fences 1.3 m high. Holes for main posts set in concrete shall be not less than 0.3 m × 0.3 m in plan, or, if round, as produced by an auger, not less than 0.3 m in diameter.
Still not sure?
If in doubt, phone a reputable fencing contractor. That's the sort of information you should be able to get from a phone call for free.
