At a glance
A garden fence built correctly by a competent DIYer will last as long as one installed professionally. The process is well within reach for anyone comfortable with a post-hole digger, a drill and a spirit level. The difference between a fence that stands for 20 years and one that falls in the first storm has very little to do with the panels – it comes down almost entirely to the posts. Get the posts right and everything else follows. This guide covers the complete build from planning rules and material selection through to first-year treatment and ongoing maintenance.
Before starting any work, check for underground services along the fence line. Gas pipes, electrical cables and water mains often run close to boundaries, particularly near the house. Call 0800 96 93 22 (Dial Before You Dig) or use the free online mapping service at hse.gov.uk to identify any buried services before you put a spade in the ground. Striking a gas main or live cable is a serious safety risk. This check takes five minutes and is not optional.
What you’ll need
Planning rules and boundaries
In England, fences up to 2 metres high can be erected without planning permission under Permitted Development rights. The one critical exception is any fence adjacent to a highway used by vehicles – this is limited to 1 metre. “Highway” is interpreted broadly and includes public footpaths alongside roads, so any boundary visible from a road should be treated as subject to the 1 metre limit. Trellis toppers count toward the total height – a 1.8m panel with a 0.3m trellis topper reaches 2.1m and would normally require permission at a rear or side boundary. Additional restrictions apply if the property is listed, in a conservation area, or subject to an Article 4 direction – these can remove Permitted Development rights entirely. New-build estates frequently have restrictive covenants in the title deeds that impose stricter height limits. Always check before starting.
Confirm the boundary before setting any posts. A fence built even partially on a neighbour’s land is a legal issue that can escalate into a formal dispute. Check your title deeds and property plan – look for T-marks on the boundary line, where the foot of the T points toward the owner responsible for that boundary. If the boundary is unclear, agree the line with your neighbour in writing before any work begins. Building 50mm inside your confirmed boundary is always the safer approach.
Choosing panels and posts
Panel and post decisions are largely independent – any panel type can be fitted to either timber or concrete posts. Choose the panel for what the fence needs to do. Choose the post material for longevity.
For posts, pressure-treated timber (UC4-rated) is the standard choice. UC4 is the British Standard classification for timber in permanent ground contact – it is what you need for any post set into soil or concrete. UC3-treated timber, which covers most fence panels, is rated for above-ground use only and will rot at the base within a few years if used as a post. When buying timber posts, check the label for the UC4 marking. Concrete posts are heavier and need two people to handle, but they are impervious to rot and genuinely last the life of the fence. Steel Metpost spikes avoid digging entirely but are only appropriate for light fencing on firm, stable ground – they work loose over time in clay or sandy soil and are not suitable for full-height privacy panels.
Arris rails are the horizontal timber rails that run between posts on a closeboard or featheredge fence, to which the vertical boards are nailed. Standard arris rails for a 1.8m fence are 75x38mm and run at three heights: approximately 300mm from the top, 300mm from the bottom, and one in the middle. On a concrete post system, the arris rails slot into notches pre-cut into the posts. On timber post systems they are either nailed or screwed directly to the post face, or dropped into metal arris rail brackets. Using brackets rather than direct nailing makes future rail replacement much easier without having to disturb the posts.
Measuring the run and handling slopes
Standard UK fence panels are 1.83m wide, so for a 10-panel fence run you need 11 posts. Before marking any positions, walk the full length of the boundary with a tape measure. The actual distance is rarely an exact multiple of 1.83m – you will almost always have a short section at one end. Plan where this falls before digging anything. The short section goes at the least visible end of the run or beside the gate where a narrower panel looks most natural. Measure the full run, divide by 1.83m, then plan accordingly.
Sloping ground is the most common complication for a DIY fence build. There are two approaches. Stepping means each panel sits level but at a different height to its neighbours, producing a stepped top line. This is the most common approach for lap panels since standard panels cannot easily be cut to follow a slope – the stepped look is widely accepted and suits most domestic gardens. Raking means the panels follow the slope continuously, with the top and bottom of each panel at an angle. This requires either bespoke cut-to-slope panels or a closeboard build where individual boards are cut to length on site. Raking looks cleaner but requires more skill and is harder to achieve with pre-made panel systems.
For a stepped fence on sloping ground, set the first post at the correct height for your intended panel height at the high end of the run. Then let each subsequent post be set independently at the height needed to bring that bay level. The difference in post height between bays is the amount the ground drops over 1.83m. Work this out before ordering posts – a run that drops 600mm over its length means some posts will be considerably taller above ground than others, and you will need longer posts at the low end to achieve the same 600mm depth in the ground.
Setting posts in concrete
This is where most DIY fences succeed or fail. The rule is one third of the total post length in the ground – for a 1.8m fence, use 2.4m posts and dig 600mm deep. Hire a mechanical petrol auger for a full fence run – digging 10 or more post holes with a hand spade is impractical and leads to fatigue-related errors in the second half of the job. A hand post-hole borer is adequate for up to three or four holes.
Before digging, run a string line from the first to the last post position to keep the run straight. Mark all positions with canes and double-check every spacing before putting a borer in the ground. Widen the base of each hole slightly to help lock the concrete footing in place. Add 75-100mm of gravel or hardcore at the base of every hole before the post goes in – this drainage layer prevents water pooling at exactly the point where timber rot begins.
For Postcrete quantities: a standard 20kg bag of Postcrete is sufficient for one post in a typical domestic fence. Gate posts, which need to be set deeper and in a wider hole, require two bags each. Order one spare bag per five posts to account for variation in hole size. Postcrete is poured dry into the hole around the post, then water is added – no pre-mixing required. It begins to stiffen within one to two minutes and sets fully in 10-15 minutes. This speed is an advantage for working through a full post run without waiting, but it means you must have the post perfectly plumb before pouring – adjustments after the mix stiffens are not possible.
Fitting panels, gravel boards and post caps
Once posts are set and fully cured, the sequence for fitting a lap panel system is: gravel board first, then panel. For timber posts, screw galvanised panel clips to the post face at the top and bottom of where the panel will sit, then drop the panel into the clips. Panel clips are the better long-term choice over direct nailing or screwing – they allow individual panels to be removed and replaced without disturbing adjacent sections or the posts themselves. For concrete posts, the panel slides directly into the pre-formed grooves on each post face, with the gravel board in a lower groove below. No fixings are needed in a groove-and-panel concrete post system.
Always fit a gravel board along the base of every panel section. A 150mm x 22mm gravel board sits between the panel and the ground, holding the panel clear of soil moisture. Without it, the bottom edge of the panel sits in contact with wet soil and rots within a few years even with pressure-treated timber. Timber gravel boards are the cheapest option but need replacing every 5-10 years. Concrete gravel boards cost a little more but are inert – they never rot and will outlast multiple sets of panels. Fitting concrete gravel boards on a new build is worth the minor additional outlay.
Post caps are often left off DIY fence builds and are one of the most common reasons timber posts fail early. The end grain at the top of every post is the most absorbent surface on the structure – rainwater soaks in and accelerates the rot that eventually works its way down into the concrete. A simple flat cap, saddle cap or decorative acorn cap nailed to the top of every post adds years to post life. They cost very little and take seconds to fit. Always cap posts before treatment so the preservative gets under the cap and onto the end grain beneath it.
Use galvanised or stainless steel fixings throughout – panel clips, arris rail brackets, screws and nails. Ordinary bright steel corrodes rapidly outdoors, and as the rust expands it forces the timber apart, creating gaps at exactly the points where the panel needs to be held firm. This is a frequent cause of panels working loose on fences that look otherwise sound. The cost difference between plain steel and galvanised fixings is negligible on a full fence build.
Fitting a garden gate
Gate posts need to be a size up from standard fence posts – 100x100mm rather than 75x75mm – and set at least 750mm deep rather than 600mm. A gate exerts continuous lateral load on the hanging post every time it is opened and closed, and particularly when it stands open in wind. An undersized or insufficiently deep gate post will work loose within a year or two of regular use.
Hang any gate over 1.2m tall on three hinges rather than two. Two hinges are adequate for lightweight gates but the upper hinge on a two-hinge system carries a disproportionate share of the load, which causes it to work loose and allows the gate to drop. Always fit a gate latch and a spring closer – a gate left standing open in wind loads the hanging post constantly and is a major cause of post failure. Hang the gate with a very slight slope toward the latch – a few millimetres lower on the latch side. This counteracts the long-term sag that affects timber gates as the wood takes on seasonal moisture, and keeps the gate operating smoothly for years longer than one hung perfectly level from the start.
Treating and finishing timber
New pressure-treated timber leaves the yard with preservative forced into the outer fibres under vacuum. What it does not have is any protection on surfaces cut after treatment. Every saw cut during installation – trimming a post to height, cutting a gravel board to length, notching an arris rail – exposes raw, untreated wood. End grain in particular absorbs moisture rapidly. All cut ends must be brushed with a compatible end-grain preservative before the cut surface is installed. Let it soak in and apply a second coat before fitting. This is the most important treatment step on a new build and the one most commonly skipped.
Once the fence is complete and fully assembled, apply a coat of fence and shed preservative to all timber surfaces – panels, posts, arris rails and gravel boards where accessible. Even pressure-treated timber benefits from a surface coat, and it also standardises the colour across sections of timber that may have varied slightly in colour from the factory. Do this in dry weather when the timber is dry, not immediately after rain. A standard 5L tin covers approximately 20 square metres of fence, which equates to roughly 5-6 standard panels depending on panel height.
Annual maintenance
When a panel eventually fails, replace it before the rot spreads to adjacent posts. A single failed panel on sound posts is a straightforward half-day job. Leaving it until the neighbouring posts are also compromised turns it into a multi-section replacement. The gravel board is the component to watch most closely – once it has rotted enough for the panel base to reach soil contact, rot in the panel accelerates rapidly. Replace a failing gravel board as soon as it shows signs of softening and the panel base will stay sound for years longer.
Removing an old fence before a new one goes in requires the same care as installation. Old concrete bases are the main challenge – the concrete around a set post is rarely small. Work the post back and forth with a length of steel bar as a lever before trying to lift it. If the concrete footing is very large, it is sometimes easier to snap the post at ground level, leave the concrete base in the ground and bore a new hole alongside it for the replacement post. The old concrete does not need to come out if the new hole is clear of it. Dispose of old timber responsibly – treated timber cannot go on a bonfire as it contains preservative chemicals. Most local household waste recycling centres accept it in the timber skip.
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