Few things look worse than a fence run dead level across a slope, leaving a wedge of daylight at one end and a buried panel at the other. Feather edge panels are rigid, so they will not bend to follow the ground — but they don't need to. Handle a gradient in panel-sized steps, set the posts at the right heights before you mix any concrete, and trim the board ends once the panels are hanging. Done properly, the fence reads as deliberate rather than improvised.
Decide How the Fence Will Follow the Gradient
Before you dig a single hole, settle on which of these the finished run will look like. It affects post heights, panel sizes and how much trimming you'll be doing.
- Stepped panels. Each panel stays perfectly level and the run drops in steps at each post. The top edge follows the gradient in even increments. This is the usual choice, and the tidiest on most garden slopes.
- Level top, stepped bottom. Easy to build and easy to regret. The gap beneath the downhill panels grows quickly, and you'll need deep gravel boards or a plinth to close it.
- Built on site. Feather edge boards cut and fixed individually to rails spanning between posts. Slower and more expensive, but it follows a steep or uneven boundary exactly, with no stepped corners.
For a typical garden fall of a few hundred millimetres, stepped panels with a gravel board under each one give the best balance of speed and neatness.
Measure the Drop and Work Out the Step
Run a taut string line from the highest post position to the lowest and check it with a spirit level, or set up a laser level if you have one. Measure the fall to the ground at each post position and write the figures down — do not trust your eye on this, especially on a long run.
Divide the total fall by the number of panels. A 480mm drop across six panels, for example, is an 80mm step per panel. That is comfortable. A step of 200mm per panel will look clumsy, so shorten the panels or switch to a site-built fence instead.
Mark the post centres with pegs. If the panels hang between posts, the centre-to-centre distance is the panel width plus one post thickness; if they screw to the face of the posts, centres match the panel width. Check the panels you have bought before you commit.
Before the spade goes in, check for buried services, drainage runs and irrigation pipework along the line. If you are unsure what is down there, get the utilities located first — it costs far less than a repair.
Dig and Set the Posts at the Right Heights
Holes should be at least 600mm deep and 200mm wide, deeper where the ground is soft or the fence takes the wind. Measure the depth from the ground at each hole rather than from a fixed datum, so every post bottom sits the same distance below the surface.
Use 100mm square posts rated for ground contact. Set the first post at the top of the slope, get it plumb in both directions, then concrete it in with a post mix, doming the concrete slightly above ground level so water runs away from the timber. Run a string line along the face of that post to align the rest.
Leave the posts long while you work and cut the tops afterwards, once the concrete has gone off, using a line and level as a guide. It is much easier to trim a post down to a marked step than to raise one that has been cut short. Give the concrete a day or two to cure before hanging anything on the posts.
Hang the Panels, One Step at a Time
Start at the end that has to line up with something fixed — a gate, a shed, an existing fence — and work along from there. Feather edge panels are heavy and awkward, so this is a two-person job.
Lift the panel into position, support it on a temporary prop and check it is level before you fix it. Screw or clip through the rails into the posts, two fixings per rail on each side. Don't overtighten; feather edge boards are thin and a screw pulled too hard will crush the timber. Check each panel against the level as you go, because a small error repeated six times stops looking small.
Trim the Bottom Edge Without Leaving Gaps
This is the stage that separates a tidy fence from one with daylight underneath. Once a panel is fixed and level, set a string line at the height you want the bottom edge to sit — around 50mm above the ground is a sensible target, so the timber stays out of the soil and can dry after rain.
- Support the panel and confirm it is level.
- Run a taut line along the underside, following the ground line between the two posts.
- Mark each board end with a pencil against a straight edge.
- Cut with a circular saw set just deeper than the board thickness, or a jigsaw for short runs. Keep the cut below the bottom rail where you can — that way the blade stays clear of nails and staples.
- Brush preservative onto every cut end as you go, before the boards have a chance to dry out.
If the bottom rail
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