How do I build a fence on a sloping garden?

There are only two honest ways to fence a slope. Stepping keeps every panel horizontal and leaves a wedge-shaped gap under each one. Raking follows the ground with no gap but needs a fence built board by board. Choosing the wrong one is what produces the fences that look like they are falling downhill.

Safety

Step by step

1. Measure the fall over the whole run.A string line level between the top and bottom of the run, and a tape down to the ground at each post position. Total fall divided by the number of bays is the step at each post.
2. Choose stepped or raked on that number.Up to about 150mm of fall per bay, stepping looks deliberate and works with off-the-shelf panels. Beyond that the steps look severe and a raked close-board fence is better.
3. Order longer posts than for a level fence.The downhill side of each post carries the step, so posts need to be longer to keep the same buried depth. Add the step height to the post length and add more again on the lowest post.
4. Set the top post first and work downhill.Establish the top of the highest post, then drop each subsequent post top by the calculated step. Working uphill means the error lands at the visible top of the fence.
5. Keep every post plumb, not square to the slope.Posts are vertical regardless of the ground. A post leaning back with the slope is the single thing that makes a hillside fence look wrong.
6. Fit deeper gravel boards to close the gaps.The triangular gap under a stepped panel is closed with a 300mm gravel board, or with two boards on the steepest bays, cut to the diagonal.
7. For a raked fence, set the rails to the slope.Arris rails run parallel to the ground, and the feather-edge boards are cut individually so their tops follow a straight rake line. The boards stay vertical; only the rail line tilts.
8. Cap the top to a consistent line.On a stepped fence, capping rails step with the panels. On a raked fence the capping follows the rake in one clean line. Mixing the two reads as a mistake.

Tips

• Do the whole layout on paper first with the measured fall. Deciding stepped or raked with posts already in the ground is expensive.
• Order gravel boards after setting the posts, when the gaps are real measurements rather than estimates.
• On a stepped fence, keep every step the same height even if the ground is uneven between posts. Regular steps look intentional; irregular ones look like a mistake.

Common mistakes

• Trying to rake a standard fence panel — A framed panel is rigid and rectangular. Cutting one to a parallelogram destroys the frame and the panel falls apart. Raking requires close-board construction.
• Using level-fence post lengths on a slope — The step at each post eats into the buried depth and the downhill posts end up too shallow. Add the step height to the post order.

If it doesn't work

Questions people ask