When planning a playground or outdoor recreation area, safety surfacing is one of the most important technical decisions to get right. The thickness of the surfacing beneath play equipment directly determines how well it protects against falls and how long it will last. Many decision-makers are unsure what the correct depth should be or how it is calculated.
Understanding playground surfacing depths ensures your installation meets safety standards while balancing practicality, appearance, and long-term value.
Playground surfacing depth is determined by the Critical Fall Height (CFH) of the equipment above it. In the UK, surfacing materials such as wet pour, bonded rubber mulch, and artificial grass must comply with BS EN 1177, which specifies the thickness required to absorb impact safely. For example, a 2.4 metre fall height typically requires around 120 millimetres of wet pour surfacing.
Why Surfacing Depth Matters
Safety surfacing does more than improve the appearance of a play area. Its primary purpose is to reduce the risk of injury if a child falls from play equipment. The depth of the surface determines how much energy it can absorb before impact reaches the ground below.
If the surface is too thin, it may fail to meet safety requirements. If it is too thick, the project may incur unnecessary costs. Striking the right balance is therefore essential for both safety and practicality.
The Critical Fall Height (CFH) test provides the standard reference point for this balance. This test measures the maximum height from which a child could fall onto the surface without exceeding safe impact levels.
The BS EN 1177 Standard
All recognised playground surfacing materials in the UK are tested and certified under BS EN 1177:2018, the European standard for impact-absorbing playground surfacing.
This standard ensures that surfacing systems such as wet pour, MulchBond rubber surfacing, and artificial grass systems are independently verified to protect users based on their thickness and structure.
During testing, a sensor measures the acceleration experienced by a headform dropped from increasing heights. The CFH value that results from these tests indicates the depth required for safe impact absorption.
Typical Surfacing Depths by Material
Different surfacing materials offer different levels of impact absorption. The correct depth depends not only on the fall height but also on the material type and the sub-base beneath it.
Below is a guide to the surfacing materials installed by Abacus Playgrounds and their typical depth requirements.
Wet Pour Surfacing Depths
Wet pour surfacing provides predictable and consistent safety performance across a range of playground designs.
| Critical Fall Height (m) | Wet Pour Surface Thickness (mm) |
| 1.26 | 30 |
| 1.36 | 40 |
| 1.65 | 50 |
| 2.04 | 60 |
| 2.24 | 70 |
| 2.47 | 80 |
| 2.60 | 90 |
| 2.62 | 100 |
| 2.82 | 120 |
| 3.00 | 130 |
Data from Abacus Playgrounds Wetpour Critical Fall Height Chart (August 2019).
Bonded Rubber Mulch Depths
Bonded rubber mulch, such as MulchBond Rubber Surfacing, provides a natural appearance while maintaining excellent impact absorption.
MulchBond Installed Over Concrete
| Critical Fall Height (m) | Rubber Mulch Thickness (mm) |
| 1.2 | 45 |
| 1.7 | 60 |
| 2.1 | 80 |
| 2.6 | 100 |
MulchBond Installed Over Natural Turf
| Critical Fall Height (m) | Rubber Mulch Thickness (mm) |
| 1.5 | 45 |
| 2.3 | 60 |
| 2.8 | 80 |
| 3.4 | 100 |
These figures demonstrate how sub-base type affects performance. Installations over natural turf require slightly greater thickness than those over hard bases to achieve the same safety results.
Artificial Grass Depths
Artificial grass surfacing combines the visual appeal of natural turf with tested fall protection through the use of impact-absorbing shockpads. It is often chosen for schools and early years areas where a natural look is preferred.
Artificial Grass (28mm pile) Installed Over Concrete with 10mm Sand Infill
| Critical Fall Height (m) | Abacus Foam Shockpad Thickness (mm) |
| 1.0 | 20 |
| 1.7 | 40 |
| 2.7 | 60 |
Artificial Grass (28mm pile) Installed Over Concrete with 10mm Sand Infill (Alternative Rating)
| Critical Fall Height (m) | Abacus Foam Shockpad Thickness (mm) |
| 0.9 | 20 |
| 1.4 | 40 |
| 1.8 | 60 |
Artificial grass systems from Abacus Playgrounds are supplied in rolls with sand infill. The foam shockpad layer provides the required safety performance while retaining the natural appearance of turf.
How to Calculate the Correct Surfacing Depth
When planning a playground, identify each piece of play equipment and note the maximum fall height. Then refer to the manufacturer’s data for the chosen surface type.
Step 1 – Determine the Fall Height
Measure from the highest playable surface, such as a platform or climbing bar, to the finished ground level. This is the critical fall height.
Step 2 – Match the Material Data
Use the data chart for your chosen surfacing. For example, if a climbing tower has a 2.2 metre platform, a 70 millimetre wet pour layer would be required.
Step 3 – Check the Sub-base
The sub-base affects performance. Surfaces laid on compacted stone or tarmac provide stable support. If the base is softer, slightly greater depth may be required to maintain compliance.
Step 4 – Maintain Even Depths
The correct surface depth should be consistent throughout the impact zone, extending beyond the equipment by at least 1.5 metres on each side where possible.
Design Considerations for Architects and Contractors
Planning surfacing depth accurately at the design stage prevents problems later in the build. Key points to consider include:
- Sub-base Preparation: The base should be level, compact, and free-draining to ensure uniform depth.
- Edge Retention: Proper edging prevents shrinkage and helps the surfacing maintain its profile.
- Drainage Planning: Even porous surfaces need well-designed site drainage to avoid water pooling.
- Transitions and Ramps: Smooth transitions between surfaces improve accessibility.
- Depth Tolerances: On-site measurements must meet the tested specification to ensure compliance.
Abacus Playgrounds provides specification advice and full documentation to help architects and contractors meet these standards.
Sub-Base and Environmental Impact
The type of sub-base has a direct influence on surfacing performance and drainage.
| Sub-base Type | Suitability | Notes |
| Compacted MOT Type 1 | Suitable for most playgrounds | Stable and cost-efficient |
| Open Textured Asphalt | Excellent drainage and long-term durability | Ideal for wet pour and resin-bound surfaces |
| Concrete | Acceptable if sloped or perforated | Allows limited drainage |
| Existing Surfacing | Possible for refurbishments | Must be structurally sound before overlay |
For schools and councils, investing in a stable, porous base ensures the surface performs consistently and remains compliant with safety standards.
Practical Benefits of Correct Surfacing Depth
Accurate depth selection improves safety while also enhancing usability and appearance.
- Comfort underfoot: The right thickness provides natural cushioning.
- Long lifespan: A consistent layer prevents premature wear or cracking.
- Better drainage: Even depth helps water flow through the surface effectively.
- Ease of maintenance: Uniform surfaces are easier to clean and repair.
- Aesthetic consistency: Correct thickness ensures even curing and finish.
These factors help create play spaces that are both safe and visually appealing for years to come.
Frequently Asked Questions
1. Can wet pour have different depths in one area?
Yes, it can be laid at varying thicknesses to match the different fall heights across a playground.
2. What happens if the surface is too thin?
A thin surface may fail to meet BS EN 1177 standards and could increase risk in the event of a fall.
3. Is thicker surfacing always safer?
Only within the tested range. Beyond that, additional thickness provides little extra benefit.
4. How is depth checked after installation?
Installers test thickness using core samples or depth probes across the surface.
5. Are different depths required under each play structure?
Yes, surfacing should be matched to the height of each item to maintain consistent safety.
6. How often should surfaces be inspected?
Visual checks every few months and professional inspections annually are recommended.
7. Can new surfacing be installed over old?
Yes, provided the existing base is stable. Abacus Playgrounds can evaluate and overlay existing installations.
8. Does surfacing depth affect colour or texture?
No, granule size and colour options remain the same regardless of thickness.
Quick Comparison of Surfacing Types and Depths
| Surface Type | Typical Thickness (mm) | Best For | Maintenance Level |
| Wet Pour Surfacing | 30–130 | Schools, councils, public play areas | Low |
| MulchBond Rubber Surfacing | 45–100 | Natural parks, woodland play areas | Very low |
| Artificial Grass | 20–60 | EYFS areas, schools, low-level equipment zones | Low |
| Resin Bound Gravel | 15–25 | Paths and walkways | Low |
(See the full Surfacing Range on the Abacus Playgrounds website for more details.)
How Abacus Playgrounds Ensures Correct Depth
Abacus Playgrounds has over 30 years of experience delivering compliant surfacing across the UK. Each project begins with an assessment of fall heights, user groups, and site conditions to determine the correct surface depth.
Our installation teams follow certified specifications, and all surfacing products are independently tested to meet BS EN 1177 standards. This ensures a reliable, safe, and durable surface for every project.
The correct playground surfacing depth is fundamental to creating safe and durable play spaces. By aligning depth with equipment height, site design, and BS EN 1177 standards, project managers and designers can ensure full safety compliance.
Abacus Playgrounds provides technical advice and installation expertise for schools, councils, and developers across the UK.
Contact our team today for professional guidance or a quotation tailored to your project.