How Deep Should Fence Posts Go to Survive Coastal Winds in Bude?

The short answer for a Bude garden

The usual rule of thumb is to bury between a quarter and a third of the post's total length. For a standard 1.8m fence in a sheltered spot, that gives 600mm in the ground. In Bude, treat 600mm as the bare minimum and go deeper for anything that faces the Atlantic.

As a working guide for exposed coastal plots:

• Fences up to 1.2m high: 450 to 600mm deep
• Fences around 1.5m high: 600 to 700mm deep
• Fences 1.8m high: 750mm deep, which means buying 2.7m posts instead of 2.4m
• Fences on cliff top or fully open plots, or in loose sandy ground: up to 900mm deep on 3m posts

Why exposure changes the sums

A solid fence panel behaves like a sail. The wind pushes on the whole face and the post acts as a lever, so the force at the base is far greater than the push at the top. An extra 150mm of depth makes a real difference to how much of that leverage the ground can resist.

Winter gales here routinely gust past 60mph, and plots in Upton, Flexbury, Crooklets and Widemouth Bay take them almost unbroken off the sea. Stratton and Poughill are more sheltered, though valleys can funnel wind in surprising ways. If your existing fence leans away from the south west or north west, that tells you where the load is coming from.

What Bude's ground does to a post hole

Ground conditions vary a lot over short distances. Near Summerleaze and Crooklets the soil can be sandy and free draining, which grips poorly, so holes need to be both deeper and wider. Further up the hill you are more likely to find clay and shillet (broken shale) over sandstone. Clay holds a post firmly but also holds water, which rots timber at ground level.

Hitting rock at 400mm is common. Do not simply stop there and hope. Either break out to full depth with a breaker, or cut a clean socket into sound rock and concrete the post into it, which can hold very well. Before any digging, check for buried cables, water pipes and drains, particularly along front boundaries where services usually run.

Making the depth count

A deep hole filled badly is no better than a shallow one. These details matter as much as the measurement:

• Dig the hole roughly three times the post width, so about 300mm across for a 100mm post
• Put 100mm of gravel in the base so water drains away from the post foot
• Use concrete, not rammed soil, and finish it just above ground level, sloped to shed water
• Choose 100 x 100mm posts as a minimum, and 125mm or concrete posts for exposed runs
• Use timber treated to Use Class 4, which is rated for ground contact
• Keep posts at 1.8m centres or closer
• Fit hot dip galvanised or stainless fixings, because salt air eats standard screws and brackets
• Consider slatted or hit and miss panels, which let some wind through and cut the load on every post

Check the height rules before you dig

Garden fences can normally be up to 2m high without planning permission, or 1m where they sit next to a road or footpath used by vehicles. Parts of Bude and Stratton fall within conservation areas, and listed buildings carry tighter rules, so it is worth checking with Cornwall Council before ordering materials. A taller fence also means deeper posts, so settle the height first.