How to add under fence plinth and fence extension?

midhatq

I have a colourbond fence atop of retaining wall. Posts are help by gal brackets on the H beams. Due to house pad level being 100 mm higher than planned, the top of concrete sleeper is about 100mm too low, meaning once I install a 100mm pathway the concrete or the garden bed will sit against the fence. I have seen under fence plinths that can be installed by removing fence panels and bottom rail and then reinstalling the fence panels. If I install a 200 mm under fence plinth my posts will be 200mm short. How do I extend the posts and don’t do any cutting of the panels.
do you supply under fence plinths?

MitchellMc

Welcome to the Bunnings Workshop community @midhatq. It's a pleasure to have you join us and many thanks for your question on fencing.

It sounds like a tricky situation, especially with the finished pad level coming in 100mm higher than planned.

If you were to install a 200mm under-fence plinth, you’re correct that your existing posts/brackets would effectively be 200mm too short. In a setup like yours (posts fixed to H-beams with galvanised brackets), you would likely need to replace all the fence brackets with longer versions designed to accommodate the additional height.

That said, I’m not aware of any off-the-shelf extension brackets that would both:

• Raise the fence height and
• Be engineered to retain soil load.

Most extension-style brackets are designed simply to elevate fencing panels and not to hold back soil. If soil is going to sit against the fence once the pathway or garden bed is installed, that introduces retaining pressure, which standard fencing components aren’t typically designed to handle. In many cases, the only structurally sound solution would be installing new, longer posts that are engineered for the revised height and load.

We do sell under-fence plinths, but they are generally intended for gap coverage (e.g. keeping pets in or debris out), not for retaining soil. If you need to retain soil, concrete sleepers or a purpose-built retaining solution would be more appropriate. The likely solution to your issue is that the retaining walls need to be redo and set at the correct height, which would be a significant undertaking, even for a retaining wall company.

Although it’s not the most convenient option, one practical approach may be installing a separate 200mm high retaining wall just inside your boundary to hold the soil back independently from the fence. That way, the fence isn’t taking any soil load.

Given the complexity and the fact that the slab height differs from the original plan, I’d recommend speaking with your builder. Retrofitting retaining and landscaping around an existing fence can quickly become costly and may require a broader rethink of how the soil is retained on your property.

It’s definitely solvable, but worth getting the structural and compliance side right before committing to a solution.

Please let me know if you have any questions.

Mitchell