One of the most frequent reasons garden fences blow over or start leaning after a winter gale is incorrect post installation. Digging a shallow hole might save time on day one, but it leaves your boundary vulnerable to frost heave and storm force winds. If you’re building a new timber or concrete fence in the UK, exactly how deep should your fence posts be buried in the ground? Here is the definitive contractor rule of thumb.
The Golden Rule: The 1/3 Rule (Minimum 2 Feet / 600mm)
In British fencing construction, the standard professional rule of thumb is:
At least one-third (33%) of the total post length — or a minimum of 600mm (2 feet) — should be set securely into the ground.
For standard residential fence heights, your post lengths and hole depths should follow these dimensions:
- For a 6ft (1.8m) High Fence: You need an 8ft (2.4m) post with 2ft (600mm) buried in the ground.
- For a 5ft (1.5m) High Fence: You need a 7ft (2.1m) post with 2ft (600mm) buried in the ground.
- For a 4ft (1.2m) High Fence: You need a 6ft (1.8m) post with 2ft (600mm) buried in the ground.
- For Heavy Driveway / Garden Gates: Posts supporting swinging gates experience dynamic rotational torque. Always set gate posts at least 750mm to 900mm (2.5 to 3 feet) deep.
How Wide Should the Post Hole Be?
The diameter of the post hole is just as important as the depth. A hole that is too narrow won’t leave enough space for concrete to surround and anchor the timber.
A professional post hole should be three times the width of the post. For example:
- A standard 75mm x 75mm (3×3″) post requires a hole approximately 225mm (9 inches) in diameter.
- A heavy-duty 100mm x 100mm (4×4″) post requires a hole approximately 300mm (12 inches) in diameter.
How Far Apart Should Fence Posts Be Spaced?
In the UK, pre-made fence panels (both waney lap and closeboard) are manufactured to a universal width of 6 feet (1.83 metres). Therefore, your post centres must be spaced exactly 1.83m apart, plus a 5mm allowance for panel brackets or slotted concrete grooves.
If you are building a continuous featheredge fence on arris rails (kit build), post centres are traditionally spaced at 1.8m or 3.0m intervals to align with standard 3.0m arris rail lengths.
3 Critical Tips to Prevent Post Rot in Ground Contact
- Add a Gravel Drainage Base: Before pouring Postcrete, pour 50mm to 75mm of coarse pea gravel or hardcore into the bottom of the hole. This allows trapped rainwater to drain away from the bottom cut of the post rather than sitting in a puddle.
- Slope the Concrete Collar: Trowel the top of the concrete so it slopes gently away from the timber post at ground level. This prevents surface rainwater from collecting around the base of the timber.
- Pair with a Gravel Board: Never let fence panels rest directly on wet turf. Use a timber or concrete gravel board to elevate the panel 150mm above wet ground.
Wooden vs Concrete Fence Posts: Which Is Best?
Slotted Concrete Posts are completely impervious to ground moisture, rot, and insects. They allow fence panels to be slid in and replaced in minutes without digging up posts. Treated Wooden Posts provide a warm, natural, seamless timber look that blends harmoniously with gardens and allows fencing to be screwed firmly in place.
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