Why Edge Restraints Matter: Keeping Paving Stable
Kerbs, edgings and restraints are among the least visible parts of a paving installation, yet they play one of the most important roles. They provide the lateral support that keeps paving units in place, helps maintain joint integrity and prevents the gradual movement/creep that can lead to pavement failure.
Without effective restraint, paving can slowly shift sideways under traffic, gravity or repeated loading. The consequences are often seen as widening joints, uneven surfaces, edge movement and a gradual loss of stability. For this reason, edge restraints should never be treated as an afterthought.
What Does an Edge Restraint Do?
An edge restraint is any feature that prevents paving units and bedding material from moving laterally.
Common examples include:
- Kerbs
- Edging units
- Channels
- Walls
- Existing structures
- Bound rows of paving
Whatever form they take, their purpose is the same: to hold the pavement together and preserve its structural integrity.
This role is particularly important in unbound paving systems, where the strength of the pavement relies heavily on interlock between neighbouring units.
Why Unbound Paving Needs Restraints
Block paving, clay pavers and many natural stone sett installations depend upon the paving units locking together.
This interlock allows loads to be distributed across the surface. If the perimeter of the pavement is allowed to move, that interlock begins to break down and the whole system becomes less stable.
For this reason, all free edges of unbound paving should be restrained. A free edge is any edge not supported by a stable structure such as a wall, building or adjoining bound pavement.
Without restraint, movement usually begins at the edges and gradually works its way into the body of the pavement.
Bound Paving Benefits Too
Although bound paving systems rely less on interlock, restraints still perform valuable functions.
They can:
- Protect exposed paving edges
- Improve appearance and definition
- Create transitions between paving areas
- Support drainage features
- Help control localised movement
In many projects, kerbs and edgings contribute as much to the overall appearance of the paving as they do to the structural performance.
Choosing the Right Restraint
The most appropriate solution depends on the project and the intended use of the paved area.
Typical options include:
Kerbs
Widely used on driveways and access routes, kerbs provide robust structural restraint and clear visual definition.
Edgings
Often used around patios, garden paths and landscape features where a less prominent appearance is preferred.
Flush Restraints
Not all restraints need to project above the paving surface. Flush kerbs, channels and bound rows of paving can provide effective restraint whilst maintaining a seamless finish.
Existing Structures
Walls, buildings and established concrete features can sometimes provide sufficient restraint without additional edging units.
Intermediate Restraints
Larger paved areas sometimes need restraint within the pavement itself, not just around the perimeter.
These are known as intermediate restraints.
Their purpose is to control lateral movement and limit creep, which is the gradual movement of paving caused by:
- Vehicle turning and braking
- Traffic loading
- Gravity on slopes
- Repeated use over time
Intermediate restraints may be formed using:
- Flush kerbs
- Channels
- Decorative features
- Bound rows of paving
They provide structural benefits whilst often contributing to the overall layout and appearance of the paving design.
Slopes Require Extra Attention
The steeper the paving, the greater the forces acting upon it.
On sloping sites of 1-20 or greater, paving units are more susceptible to movement created by both gravity and traffic. Intermediate restraints are therefore need to be installed closer together than they would be on level ground.
The aim is to divide larger areas into smaller sections that are better able to resist movement and maintain long-term stability.
Restraints Need Proper Support
An edge restraint is only effective if it is properly supported.
Kerbs and edgings should be installed on suitable foundations and backed by concrete haunching. Without this support, the restraint itself may move, compromising the pavement it is supposed to protect. Edge restraints should be haunched and bedded as a monolithic unit. Haunching should not be installed the day after bedding, as you lay the edges restraints. Edge restraints should have a vertical face below the laying course/bedding. Haunching should travel a minimum 50% up the side of the edge restraints, a c25, moist concrete is the preference.
The restraint and its support should be thought of as part of the pavement structure rather than a decorative feature added at the end of construction.
Strong Edges Create Durable Paving
Many paving failures begin at the perimeter. Movement at the edge allows interlock to weaken, bedding material to escape and alignment to deteriorate.
By selecting appropriate restraints, positioning them correctly and ensuring they are adequately supported, landscapers create the framework that allows the pavement to perform as intended. Strong, stable edges help maintain the appearance, safety and durability of the paving for many years after installation.
