

Retaining a 200 to 400 mm drop under an existing Colorbond fence: dry-stack block wall plan
G'day everyone,
Looking for a sanity check on a plan to retain a boundary drop beneath an existing Colorbond fence.
The Situation
- The neighbour's yard sits 200 to 400 mm higher than ours across a 20-metre boundary.
- The previous owner's temporary fix of loose bricks, timber offcuts, and reed screening is finally giving up.
- I need a clean, permanent solution with proper drainage that will not put lateral load on the fence posts. (Photos attached: current state)
The Plan: Freestanding Dry-Stack Wall Rather than bolting plinths or sleepers to the fence posts, I am planning an independent, low dry-stack block wall (looking at Brighton Eziwall, Hudson Stone, or similar) sitting just on our side of the boundary.
- Trench and base. Dig down 120 to 150 mm, lay 75 to 100 mm of road base, and compact it thoroughly.
- Base course. Bury roughly half of the first block below finished ground level to prevent kick-out.
- Height and stepped run. Stack 3 to 4 courses (300 to 400 mm total), stepped along the natural fall. Glue the cap/top course down with landscape adhesive (Sikabond or similar).
- Fence gap. Maintain a 15 to 20 mm gap under the bottom Colorbond rail to prevent rust from trapped moisture.
- Drainage. 65 mm socked ag-pipe behind the first course, surrounded by 20 mm blue metal wrapped in geotextile fabric, draining to a lower point in the yard.
Questions
- Trench prep. For a 3 to 4 course wall at this height, is well-compacted road base enough, or is a concrete footing worth the extra effort on a mild slope?
- Alternative setups. Has anyone tackled a similar drop with a modular system they preferred over dry-stack blocks?
- Drainage details. Any practical tips for keeping the backfill free of silt over time without creating an awkward channel behind the fence?
Keen to hear your thoughts or spot any glaring mistakes before I order materials.
Cheers!