Ensuring Strength and Longevity
Retaining walls might look like simple garden features or landscaping tools, but from a structural engineering perspective, they are anything but. These walls work hard behind the scenes — holding back soil, managing ground levels, and protecting against movement or collapse.
Whether you’re building on sloping ground, creating a level terrace, or dealing with potential subsidence, a retaining wall is often a critical part of the structure — and it needs to be designed properly.
Here’s everything you need to know about retaining walls from a structural engineer’s point of view.
What Is a Retaining Wall?
A retaining wall is a rigid structure built to support soil laterally, preventing it from slipping or eroding away. It holds back earth at different ground levels — common in sloped gardens, cut-and-fill sites, driveways, and during basement construction.
But unlike a decorative garden wall, a retaining wall must resist significant lateral pressure from the soil it supports — especially when wet or unstable.
When Is a Structural Engineer Needed?
If your retaining wall is:
- Over 1 metre high near public footpaths or roads
- Over 1.5 metres high in general
- Retaining significant weight or buildings
- Near neighbouring boundaries (triggering party wall considerations)
- Part of a basement or below-ground structure
…then it’s essential to involve a structural engineer.
Without proper design, a retaining wall can crack, bulge, lean — or even fail completely, posing a serious safety risk.
Key Engineering Considerations
1. Soil Pressure & Type
Soils behave differently. Clay expands and contracts. Sand can shift and erode. The wall must be designed to withstand active earth pressure, surcharge loads, and changes in moisture content.
2. Drainage
Poor drainage is a leading cause of retaining wall failure. Water builds up behind the wall and increases pressure dramatically. We design for:
- Weep holes
- Drainage layers
- Geotextiles
- Perforated pipes or gravel backfill
3. Wall Type & Materials
We design based on site conditions, appearance, and budget. Common types include:
- Gravity walls – rely on their mass (e.g. stone, concrete blocks)
- Cantilever walls – reinforced concrete walls with a footing
- Counterfort walls – stronger cantilever walls with internal supports
- Sheet pile walls – used in soft soils or tight spaces
- Anchored walls – stabilised with ground anchors in steep or tall situations
4. Foundation Design
Just like any structure, a retaining wall is only as good as what it sits on. Shallow or poorly designed footings can lead to rotation or settlement.
Common Retaining Wall Applications in the UK
- Split-level gardens and sloped driveways
- New builds on hilly or uneven sites
- Basements and lightwells in residential homes
- Structural landscaping in commercial or public projects
- Flood prevention or land stabilisation near watercourses
In areas like Sussex, where varied topography, clay soils, and coastal erosion are common, well-designed retaining walls are often essential.
Building Regulations & Legal Considerations
In the UK, retaining walls may not always require planning permission — but they must comply with Building Regulations, especially where they support structures or impact safety. Party Wall Agreements may also apply if the wall is close to neighbouring properties.
It’s also important to check land ownership, boundary lines, and local authority requirements before starting work.
Signs a Retaining Wall May Be Failing
- Cracking or bulging
- Leaning forward
- Water seepage or erosion behind the wall
- Pooling water at the base
- Settling or gaps forming around the top
If you see any of these, it’s time to consult a structural engineer — early intervention can prevent costly repairs or replacements.
Need Expert Advice?
At Sussex Structural Engineers, we’ve designed and assessed retaining walls for projects of all sizes — from garden terraces to large-scale developments. We understand the unique challenges posed by the ground conditions and landscapes across the UK, especially in the South East.
Get in touch today for expert advice tailored to your site and project.