Colorbond Fence on a Sloping Block: A Sydney Guide

On a flat block a Colorbond fence is straightforward. On a slope you have to decide how the fence follows the ground, and that single decision changes how the finished fence looks, how much site preparation is involved, and what the job costs. There are two accepted ways to do it: step the panels down the slope, or rake them so they run parallel with the ground. Plenty of Sydney boundaries end up with a bit of both along the same run.

Stepped or raked: the two ways down a slope

Colorbond panels are made square. That means the sheets, rails and posts all want to sit level and plumb. On sloping ground you either keep the panels square and step them, or you cut the sheets on an angle so the whole panel rakes with the fall.

Stepped panels

Each panel stays level and each one sits a little lower than the last, so the top of the fence looks like a set of stairs. It is the more common approach on Sydney blocks because it uses standard panels with minimal cutting.

• The top line stays crisp and level on every panel, which suits a front or street-facing boundary.

• It creates a triangular gap under the high end of each panel that has to be dealt with, usually with plinth boards or a small amount of retaining.

• Steeper falls mean bigger steps, so on a sharp slope the steps can start to look heavy from the street. Shortening the panel spacing keeps the steps smaller.

• Post heights all differ, so post depth and panel setout need to be marked out properly before any concrete goes in.

Raked (sloping) panels

The rails and sheets are cut on an angle so the fence follows the ground in a continuous line. It looks neater on a long, even fall and it closes off the gap at the bottom without extra infill.

• Best on a consistent, gentle-to-moderate fall. On uneven ground you end up raking to an average line and still have gaps to chase.

• Every sheet is cut, so there is more labour and more waste than a stepped run.

• Cut edges need to be handled properly. A raw cut edge on a steel sheet is where corrosion starts, which matters more near the coast.

• Gates still have to be square, so a raked fence usually needs a stepped or level section either side of a gate opening.

The gap under the fence is the real problem to solve

Most complaints about fences on slopes are not about the top of the fence, they are about the bottom. A gap under a stepped panel lets soil and mulch wash through, lets small dogs out and cats in, and looks unfinished. The usual ways to close it:

• Plinth or retaining boards along the base, timber or concrete, held by the fence posts and backfilled to level.

• Cutting the bottom of the sheets to the ground line, which is effectively a partial rake on an otherwise stepped fence.

• Regrading a narrow strip along the boundary so the ground meets the panel more evenly.

• A low retaining wall along the fence line where the level change is more than a plinth board can hold.

• Gravel or a paved mowing strip, which handles a small gap and stops soil washing under.

Whichever way it goes, it should be spelled out in the quote. A fence priced as bare panels and posts on a sloping block is a fence with a gap under it.

When the slope needs a retaining wall, not just a fence

A fence holds itself up. It does not hold up ground. Once there is a genuine level difference between the two sides of a boundary, that ground needs a retaining structure, and the fence sits on top of it or behind it. Trying to make a fence do the retaining is how you end up with leaning posts and bowed panels a couple of years later. We cover the options in our guide to retaining walls in Sydney, and there is more on how we approach combined jobs on our retaining walls and fencing page.

Retaining work is also where approvals come in. Height thresholds, setbacks and whether engineering is required vary between councils, and a wall that also affects a neighbour's ground has its own considerations. Check the requirements with your own council and the NSW Planning Portal before committing to a design, and see our post on council approval for a fence in Sydney for the general picture.

Posts and footings on sloping ground

Post depth on a slope is measured from the low side of the hole, not the high side. That sounds obvious and it is still the most common shortcut we find on failed fences: a post that looks deep from uphill and has almost nothing holding it downhill.

• Fill and made-up ground need more depth than undisturbed soil. Terraced blocks and old cut-and-fill sites are full of both, often in the same run.

• A sandstone shelf close to the surface is common through the Sutherland Shire and the North Shore. It is excellent to found on, but it means drilling rather than digging, and post positions sometimes have to shift slightly.

• Reactive clay through the Hills District and parts of south-western Sydney moves with moisture, so footings want to get below the zone that dries out and swells.

• On a steep site the hole for an uphill post can undercut the ground the downhill post is sitting in. Sequencing and concreting order matter.

Water has to go somewhere

A fence running across a fall acts like a small dam, and plinth boards or a retaining course make it a better one. In a heavy Sydney downpour that water will find the weakest point, which is usually a neighbour's yard or the base of your own posts.

Practical measures are simple: leave deliberate drainage points in the plinth line rather than sealing it completely, run drainage gravel and an agricultural line behind any retaining course, and keep soil and mulch levels below the bottom of a steel sheet so the base of the fence is not sitting permanently damp.

What to check before you accept a quote

• Does it say stepped or raked, and if stepped, what the step height and panel spacing will be?

• How is the gap under the fence closed, and is that material included or an extra?

• Is any retaining included, and if so, is engineering or council approval required for it?

• Who removes and disposes of the old fence, and how will material get to a sloping or rear boundary with no vehicle access?

• Are cut edges on raked sheets treated, and how?

• If it is a shared boundary, has the cost-sharing conversation happened? Our post on who pays for a dividing fence in NSW covers how that normally works, and fencing costs in Sydney explains what moves the price.

Common questions

Is a stepped or a raked Colorbond fence more expensive?

Raking usually costs more in labour because every sheet is cut and the setout takes longer. A stepped fence can close the gap back up with plinth boards, which adds material cost. Which one works out dearer depends on the block, so it is worth asking for both to be priced on a genuinely sloping boundary.

How steep is too steep for a Colorbond fence?

There is no single cut-off. What matters is whether the fall can be handled with steps or a rake without creating gaps you cannot close, and whether the ground is stable enough to hold posts. On a sharp fall the honest answer is often that part of the run needs retaining first.

Can I fill the gap under my existing fence myself?

On a small gap, gravel or a paved mowing strip is a reasonable do-it-yourself job. Anything that involves holding back soil is retaining work, and that is worth getting right the first time, because the fence above it depends on it.

Will a sloping block change the fence height I am allowed?

Height is generally measured from natural ground level, which on a slope is not a single number along the run. Front fences and boundaries in conservation areas often have their own controls. Confirm with your council, and see our guide to Colorbond fence heights for how the standard sizes work.

Does a raked fence still suit Colorbond?

Yes. Colorbond is well suited to it because the sheets can be cut cleanly to a line. The trade-off is that cut edges need to be finished properly, and near the coast that matters, which is one of the points we make in our post on the best fence for coastal Sydney homes.

Getting it priced properly

Sloping boundaries are where quotes diverge most, because two contractors can look at the same fall and plan two different jobs. We walk the line, take the levels, and put the method in writing before anything starts. You can read more about our Colorbond fencing work, browse all of our fencing services, or check the areas we service across Sydney.

If you have a fence to do on a slope, get in touch for a quote and we will tell you plainly whether it is a stepping job, a raking job, or a retaining job first. The same raked-versus-stepped thinking applies to a vehicle gate - see our guide to Colorbond driveway gates. Also worth reading: how long fence replacement takes in Sydney.