Sleepers vs Retaining Walls: Understanding the Difference Beneath Your Fence
- Glovers Fencing
- 6 days ago
- 4 min read
Sleepers Under a Fence vs Retaining Wall Sleepers — What’s the Difference and Which Do You Need?
Your home is more than walls and a roof — it’s where memories are made, where you unwind, where every detail contributes to comfort and beauty. So when you build a fence, or when you build a retaining wall (or a fence atop a retaining wall), you want things done right. One critical decision you may come across is whether to use sleepers under a fence or as part of a retaining wall system. Though they might look similar at first glance, the two uses bring different demands, challenges, and best practices.
Let’s walk through what sleepers are, how they work in each scenario, and when one approach might be more suitable than another.
Sleepers Under a Fence - Without Heavy Earth Retention:
Purpose & Function
When placing sleepers under a fence, their primary roles may include:
Elevation & levelling — They help lift the fence off the ground slightly, prevent direct contact with soil (moisture, termites), and compensate for uneven terrain.
Anchoring & stability — They give posts a robust footing and help distribute loads, especially in lighter soils or in high-wind zones.
Aesthetic transition — Sleepers can create a visual “base” to the fence, especially in designs where the lower section uses horizontal beams or decorative treatments.
In this scenario, the sleeper doesn’t need to resist large lateral soil pressures. The loads are moderate (wind, occasional knocks, leaning), and drainage or drainage conflicts are less severe.
Key Considerations & Best Practices
Material choice — Durable, treated timber (e.g. H4 preservative), composite, or concrete are common. Timber must be chemically treated to resist decay.
Size & section — A thicker sleeper (e.g. 150×50mm or even greater) gives stiffness, reduces sagging over time.
Fixing & joinery — Secure connections to fence posts and proper end supports are essential. Bolts, brackets, or embedded steel straps help.
Clearance & drainage — Provide a small gap between tensioned soil or mulch and the sleeper to ensure moisture drains away. Prevent pooling and wood rot.
Because these sleepers are not retaining heavy loads, their design is more forgiving and less complex.
Sleepers in Retaining Walls & as Retaining Wall Components:
When you use sleepers as part of a retaining wall, especially where earth must be held back - the structural requirements are far more rigorous. Here, the sleeper becomes a structural member resisting significant lateral earth pressure (soil + water), plus any surcharge loads.
Purpose & Function
In a retaining context, sleepers may serve to:
Provide lateral support to prevent soil movement or collapse
Distribute loads along their length
Interface with drainage systems (weep holes, pipes, gravel)
Act together with posts, anchors, tie-backs or deadmen beams
Key Considerations & Best Practices
Structural design & engineering — You’d often want a geotechnical and structural engineer’s input, especially for walls above a modest height (e.g. more than ~1 m). The wall must factor in soil type, groundwater, surcharge loads, etc.
Material & thickness — Timbers used must be very robust, pressure treated for ground contact, often of larger cross section. Concrete or steel “sleepers” may be more appropriate for significant loads.
Anchoring / reinforcement — The use of tiebacks, steel reinforcement, deadmen posts, anchor rods or cables is common to resist overturning and overturning moments.
Drainage is critical — Backfill material should be free-draining (gravel, coarse aggregate), with drainage pipes or weep holes. Poor drainage leads to hydrostatic pressure, which is one of the most common failure causes.
Footings & base preparation — The base (or footing) of the retaining sleeper must be firm and level, sometimes with compacted aggregate or concrete foundation, to prevent settlement or sliding.
Control of rot, corrosion, moisture — Because sleepers are retaining soil, they're always near moisture and possibly wet. Adequate preservative treatment and potential encapsulation or protective coatings help with durability.
Side-by-Side Comparison
When to Use Each, or Combine Them?
Low retaining need + fence on level ground — If your site is roughly level and the fence is simply to mark boundaries or provide privacy, using sleepers under the fence is adequate.
Sloping block, or changes in grade — On sloped land, where soil retention is necessary, you’ll likely need a retaining wall. You might combine sleepers (as retaining elements) with the fence mounted above.
Height & loads — If the retaining effort is minimal (say a small garden bed of 200–300 mm), you might treat it like a “raised garden border” and use sleepers with careful drainage. But beyond that, full retaining wall design is advised.
Budget & longevity tradeoffs — The more structural the requirement, the more cost and engineering involved — but also the more risk if done wrong. The difference in cost is often small compared to repairs later from failures.
It’s a common misunderstanding — but sleepers under a fence aren’t a substitute for a retaining wall. They’re there to protect the fence line, not to hold back soil. If your property needs soil retention, that work needs to be completed by a qualified retaining wall builder first, so your new fence can be installed correctly for longevity.
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