How a Fence Should Be Installed

Work starts with a string line pulled tight between the two ends of the run. Every post is set to that line, and the line stays up throughout — eyeballing a fence over twenty metres produces a visible curve.

Post positions are marked at accurate centres. For standard 1.83m panels, posts are set at 1.83m plus the post width, and any error accumulates: three centimetres out on each of eight bays means the last panel does not fit.

Before digging, check for buried services. Water pipes, electricity supplies, gas connections and drainage runs frequently follow boundaries, and a cable detector plus a careful hand dig for the first spit is standard practice on any garden a contractor has not worked on before.

This is also the moment to confirm the line is on the correct side of the boundary and, where relevant, that the neighbour is aware. Moving a completed fence 150mm is not a small job.

Post holes should be at least 600mm deep for a 1.8m fence — a quarter of the total post length in the ground is the working rule — and roughly three times the post width across, so there is space for concrete all round.

Postcrete or a standard concrete mix both work. What matters is that the post is held on all sides, plumb in two directions, and braced until the concrete has gone off. A post nudged out of plumb while the concrete is green stays out of plumb permanently.

The top of the concrete collar should be finished above ground level and domed or sloped away from the post so that rainwater runs off. A concrete collar finished flat or dished creates a permanent puddle around the timber, which is exactly where rot starts.

In soft, waterlogged or made ground, holes may need to be deeper or wider. On the shrinkable clay found inland in Essex, posts set too shallow are gradually worked loose by seasonal ground movement.

A gravel board runs along the bottom of each bay between the posts, taking the contact with the ground so the panel or the featheredge boards sit clear of soil and splash.

Concrete gravel boards are the durable option and are worth specifying on any fence intended to last. Timber ones are cheaper but become the first component to rot, though they are at least easy to replace.

The gravel board also sets the base line of the fence. On uneven ground, boards are stepped or the ground is dressed so that the gap beneath stays small — a fence with a 100mm gap under one bay is not doing its job as a boundary and loses much of its stiffness.

Where soil levels differ significantly across a boundary, a low retaining detail may be needed rather than simply banking soil against the fence. Soil pressure against fence boards is a common and avoidable cause of failure.

Panels sit in the slots of concrete posts or are fixed to timber posts with panel clips or brackets. They should never be nailed straight through the frame into the post — the timber splits and the fixing pulls out.

Closeboard is built in place: arris rails are jointed into the posts, then featheredge boards are nailed on with a consistent overlap of around 25mm, each board fixed so that the nail passes through only one board at that point. Nailing through two overlapping boards prevents them moving with humidity and causes splitting.

Every fixing should be galvanised or stainless. Ordinary steel nails and screws bleed rust down the timber within a year, and near the Essex coast the salt air accelerates it markedly.

Post caps are a small detail with a real effect. An uncapped timber post absorbs water through its end grain and rots from the top down, often long before the buried section fails.

There are two ways to handle a slope. Stepping means each panel stays horizontal and drops down a step at each post, leaving triangular gaps at the bottom that need infilling with soil or a stepped gravel board.

Raking, where the fence follows the ground line, avoids the gaps and looks far neater. Standard prefabricated panels cannot rake, so this is a closeboard technique — the arris rails are set parallel to the ground and the boards are cut to follow.

On a gentle slope, raked closeboard is almost always the better result. On a steep one, a combination of stepping with short retaining sections may be the only practical approach.

Whichever is chosen should be agreed before work starts. It changes both the appearance and the price, and it is the most common source of disappointment on a sloping boundary.

New pressure-treated timber should be left to weather for a few months before any stain or paint is applied — the treatment leaves the timber too wet to accept a finish, and coating it early traps moisture in.

Once weathered, a penetrating preservative or a quality fence stain applied every two to three years extends life considerably. Film-forming paints look good initially but flake, and stripping a flaking fence is thankless work.

Give the concrete at least twenty-four hours before hanging gates or applying any load, and longer in cold weather.

Finally, a quick annual check pays for itself: push the top of each post firmly, look for movement at the base, check that soil has not built up against the boards and that no climber has taken over. Five minutes each spring prevents most of the failures we are called out to.