Offcut WorksFence on a slope calculator
Panel fencing on a slope is built in steps, with each panel kept level. Enter the length of the run and how far the ground falls. You get the post lengths, the size of each step, and the gap to fill under the panels.
How the numbers are worked out
Bays = run ÷ post spacing, rounded up. Drop per bay = total fall ÷ bays. For a 10 m run at 1.88 m spacing: 10 ÷ 1.88 = 5.3, so 6 bays. A 600 mm fall gives 600 ÷ 6 = 100 mm per bay.
Panels stay level. Each panel is set with its bottom at the ground at its higher end, so the gap at its lower end equals the drop across it.
Posts. A post must be flush with, or slightly higher than, the highest panel it holds. So a post where the fence steps down stands one step taller above its own ground than the post at the top of the run. The post length is the panel height, plus the step, plus the depth in the ground. In the example, the first post is 1,800 + 600 = 2,400 mm and the other six are 2,500 mm.
Panels per level. You can step at every post, or hold two or three panels at one level and step down by more. The steps then get larger, and so do the gaps.
Stepped or raked?
Jacksons Fencing says traditional kit-form fencing, built from pales and rails, can follow a gradual slope, which is called raking. Panel fencing with slotted posts is stepped instead, and each panel stays level. Angled panels would need angled posts, which look poor and weaken the fence. This calculator covers stepped panels only. For raked fencing, ask the maker, because we did not find a published limit.
Gaps under the panels
Stepping leaves a triangular gap under each panel, which is deepest at its lower end. Jacksons suggests setting gravel boards partly into the ground, or stacking several, to close it. Without boards, large gaps leave the panel exposed to the ground and shorten its life. The calculator shows the deepest gap and about how many boards of your height that is.
Exposed post slots
Where the fence steps down, the top of the post shows above the lower panel. On slotted posts, an infill piece fills the empty slot above that panel. Measure each gap, cut the timber to size, and treat the cut end.
Spreading the steps
Measure the height difference across the whole run and step down evenly. Jacksons also suggests stepping every few panels. The page gives no maximum slope or step size, so check with your panel maker if the fall is large.
The 2 metre planning limit
A fence of up to 2 metres is permitted development away from a highway used by vehicles. The Order measures height above ground level, and a stepped fence on a slope is not clear-cut. At its tallest, a post stands one step above the panel height. If you are close to 2 metres, ask your council. The fence panel calculator has a quick check.
Gates on slopes
A gate on a slope needs clearance underneath to swing, which makes it harder to fit. Plan for it separately.
Questions
Should I step or rake fence panels on a slope?
Jacksons Fencing says panel fencing with slotted posts is stepped, with each panel kept level, while traditional kit-form fencing can rake to follow a gradual slope. Check your maker's instructions before raking a panel.
How do I work out the step for each panel?
Divide the total fall by the number of bays. Each panel then sits that far below the one before. The calculator does this and gives the post lengths.
How long should the posts be on a slope?
A post should be flush with, or slightly higher than, the highest panel it holds. Where the fence steps down, it needs to be one step longer than at the top of the run, plus the depth in the ground.
What do I do about the gap under a stepped fence panel?
Use gravel boards. Set them partly into the ground, or stack several, so the gap under the lower end is closed.
Where the defaults come from
Show the 3 sources
- Jacksons Fencing, installing stepped fence panels on a slope. A UK manufacturer's guide. Raking for kit-form fencing and stepping for panels with slotted posts, evenly or every few panels. Posts flush with or slightly higher than the highest panel. Gravel boards set into the ground or stacked, and infill pieces for exposed slots. It gives no maximum slope or step size.
- Dino Decking, fencing on a slope. Measuring rise and run, and stepped fencing for steeper slopes.
- Planning Order, Schedule 2, Part 2, Class A. The 2 metre limit above ground level, and 1 metre next to a highway used by vehicles.
- We found no manufacturer's maximum slope or maximum step per panel. Check your panel maker's guide if the fall is large.
- The post length is geometry that follows the Jacksons rule that a post is flush with or higher than the highest panel. It is not a published table.
- The calculator assumes the ground falls evenly along the run. A hump or dip needs measuring in sections.
- The 600 mm post depth and the 1.88 m spacing are the defaults used on our fence panel calculator.
- The 150 mm gravel board is an example. Gravel boards vary, so enter yours.
- We found no source on how a council measures the 2 metre limit on a stepped fence on a slope.