Retaining wall types: sleeper, crib and king post walls explained

What a retaining wall actually has to resist

Soil pushes sideways, and wet soil pushes much harder than dry. Most retaining wall failures are not a weak face but water building up behind it with nowhere to go. That is why any sensible design includes a free draining backfill and a way for water to escape at the base.

Sleeper walls

Timber sleepers stacked horizontally, fixed to posts set into the ground. They are quick to build, look natural against planting, and suit raised beds and gentle terraces.

Timber is a natural material and will eventually need replacing, so treated or durable timber and a lining against the soil face help it last. Height is the limiting factor; taller sleeper walls need a proper structural approach.

Crib walls

A crib wall is a cellular frame of interlocking units, filled with stone or gravel. The weight of the fill does most of the work, and the open structure drains well. They are often chosen for longer banks and road or driveway edges, and can be planted to soften them.

King post walls

Steel posts are set in concrete at intervals and panels, usually concrete or timber, drop into the channels between them. They handle bigger loads and taller faces than a sleeper wall and are common where a driveway or building sits above the retained ground.

Because the loads are higher, taller king post walls typically need engineering input on post depth and spacing.

Choosing between them

A quick way to narrow it down:

• Low change in level and a garden feel: sleepers.
• Long bank or slope that needs to drain well: crib wall.
• Taller face, or a drive or structure above: king post.
• Any wall near a boundary or a neighbour's ground: talk to them and check your responsibilities first.

Drainage behind the wall

Whichever wall you choose, the backfill behind it should be free draining, usually clean stone rather than the soil that was dug out. A perforated drain pipe at the base, wrapped to stop silt blocking it, carries water to a soakaway or suitable outlet. A membrane between the soil and a timber face slows rot. These parts are hidden once the job is finished, which is exactly why they are sometimes left out of cheaper quotes, so check they are listed.

Planning the wall with the rest of the garden

Walls rarely stand alone. Steps through the level change, a path along the top, lighting and planting all affect where the wall sits and how tall it needs to be. Settling those details first saves altering a finished wall later.

Questions we're asked about this