Retaining Wall Construction: What Happens On-Site, Step by Step

Site Assessment and Setout

Before any digging starts, the wall line is set out based on the engineering design (for walls that require one) or an agreed plan for lower garden walls, accounting for the final levels wanted on both sides of the wall, boundary position, and any services or structures nearby. A Dial Before You Dig check is a standard step here to confirm underground services before excavation begins.

Excavation for the Wall Line

Excavation follows the wall’s footprint, removing soil to the depth needed for the footing or post holes and creating a working area to build the wall itself. On sloping or constrained sites, access for machinery is planned at this stage too — see our guide on excavation day for what this typically looks like more broadly.

Footings and Posts

This is the stage that determines how the finished wall will actually perform. Concrete is poured for strip footings or post holes, or bored piers are installed, to the depth and specification set by the engineer or standard practice for a low wall. See our footings guide for why this stage matters as much as anything visible in the finished wall — it’s also usually inspected before work continues, since footings can’t be corrected once the wall is built on top of them.

Building Up the Wall

With footings and posts in place, the wall itself goes up — sleepers slotted between posts for concrete or timber sleeper walls, or the relevant construction method for other engineered systems. This stage is generally faster than the footing stage, since most of the load-bearing work is already resolved by the time the wall face starts going in.

Installing Drainage as the Wall Goes Up

Drainage isn’t an afterthought added once the wall is finished — agricultural drains, drainage cell or gravel backfill, and weep holes are typically installed as the wall goes up, so water has a genuine path away from behind the wall from day one. See our drainage guide for how this system works as a whole.

Backfilling Correctly

Backfill material and how it’s compacted behind the wall genuinely affects both drainage performance and the load the wall has to resist — free-draining material like gravel is typically used directly behind the wall rather than the original clay-heavy soil, which holds water and adds pressure. Backfilling is usually done in stages, compacted as it goes, rather than dumped in all at once.

Finishing and Capping

Once the wall and backfill are complete, finishing touches like capping, final grading above and below the wall, and reinstating any garden beds or turf bring the project to completion. This is also when any fencing that sits on or near the wall is typically addressed, if relevant to your project.

Inspections Along the Way

For walls requiring a permit or engineering sign-off, inspections at key stages — typically footings, and sometimes the completed structure — confirm the work matches the approved design before it’s covered up or finished. This is one of the genuine reasons unpermitted work on taller walls carries real risk: there’s no independent check that the footing and drainage were actually built to a standard capable of holding the wall long-term.

What Can Affect the Sequence

Weather, access constraints, unexpected ground conditions found during excavation, and the need for engineering revisions if soil conditions differ from what was expected can all affect how this sequence plays out on a specific site. A contractor who explains where your project might hit one of these variables — rather than promising a fixed timeline regardless of conditions — is generally giving you a more realistic picture of what to expect.

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