PP50 Design Guidelines with Gravel

Suregreen PP50 Design Guidelines

50mm Permeable Paving Grids with a Gravel Finish

All of our design guidelines are written with best practice in mind. It is strongly advised that any questions raised from the guidelines are directed to our technical team.

When Suregreen PP50 gravel grids are installed correctly to suit site conditions, they should provide source control within a SuDS system (Sustainable Urban Drainage Systems). Drainage must be a consideration when designing a construction profile to ensure that flood alleviation and water run-off is properly considered where natural filtration may not be capable of withstanding all eventualities.

Download PP50 Gravel Finish Design Guidelines

Questions to be considered

a). Does the proposed installation area drain well already? 

b). Is there planned to be a slight fall to be built into the design to aid drainage, if aid is needed?

c). Is the drainage capability of the soils the same at the surface and at 200 - 500mm below the surface?

d). Have there been previous issues with drainage on site?

e). Has disposal of any excess water been considered?

f). Are there SuDS requirements to be considered?

We would advise speaking to our technical team regarding any of these questions for further guidance.


  1. If a geogrid is being considered as part of the construction profile, please ensure that at least 25% of the particle size of the sub-base is bigger than the mesh size of the geogrid to ensure good shearing/locking.
  2. Sub-base particle size ideally should not exceed 60mm and should be less than 5% fine material of content of the whole. Please contact us for technical guidance if you are unsure.
  3. Please refer to tables 1 & 2 for guidelines to the depth of sub-base for specific design profile to suit different site needs. Please note - if a geogrid is omitted, 50% of the depth of sub-base needs to be added to calculated depth with a geogrid. For example, 100mm with geogrid would become 150mm without. For detailed guidance please contact our technical team.
  4. It is always good practice to confine PP50 plastic pavers on the site edges. This could be with something as strong as 150 x 150mm concrete kerbs or a simple barrier such as treated timber. The type of vehicles, frequency of traffic and circulation routes should all be considered when choosing the confinement method for PP50 in the design.
  5. PP50 permeable pavers have been designed to work within stated guidelines to a slope of 5% or less. PP50 can be used on steeper slopes up to 15% - please enquire to our technical team for guidance.
  6. Ideally, the sub-base should extend out further than the surface area of PP50 porous paving grids. This is so that lateral pressures caused by the traffic loading does not displace the PP50 on the edge. The extension of sub-base outwards should be the same as the depth of the sub-base. Please see the schematic for detail.
  7. The aggregate for the bedding and the filling of the cells should ideally be specified as 5mm - 20mm sharp angular gravel to BS EN13242. This gives the best results for providing a long-term, very low-maintenance and hard-wearing surface. The gravel pieces interlock/shear with each other and, more importantly, with the specially designed PP50 plastic paver. The smaller gravel particles fill the voids to provide a secure, stable and sustainable finish. Single size gravel or rounded gravel/pea shingle will lead to issues and failure. The more rounded and single size the gravel, the faster problems are likely to happen.
  8. When filled with aggregate 5mm to 20mm to BS EN13242, PP50 gravel-filled paving conforms to BS8300:2001 for disabled access.


Note on drainage

Any sub-base used in the construction profile should be permeable - for example, MOT Type 3. It should be predominantly fine material-free and able to compact well without losing integrity, stability and permeability. MOT type 1 can be used, but drainage channels need to be considered – please see the schematic. 

For any detail on specification for design not covered in the above, please contact our technical team.

Table 1 – Typical Sub-Base Thickness (with/without geogrid)


CBR % (Strength of Subgrade Soil)

Sub-base Thickness

Light Vehicles, Cars, Vans and Overflow Parking

= 1 < 2


= 2 < 4


= 4 < 6


= ≥ 6


Lorries, Coaches, Fire Engines and Occasional HGV usage

= 1 < 2


= 2 < 4


= 4 < 6


= ≥ 6


 *If a geogrid is not used, sub-base thickness should be increased by 50% 



Table 2 – Field Guidance for estimating sub-grade strengths





Tactile (feel)


Mechanical (test)







Very Soft

Hand sample squeezes through fingers

A man standing will sink > 75mm


< 2


< 1


< 25



Easily moulded by finger pressure

A man walking sinks 50 – 70 mm


2 - 4


Around 1


Around 25



Moulded by moderate finger pressure

A man walking sinks 25mm


4 - 8




25 - 40



Moulded by strong finger pressure

A Utility truck ruts 10-25mm


8 - 15


2 - 4


40 - 75



Cannot be moulded but can be indented by thumb

Loading construction vehicle ruts 25mm




4 - 6


75 - 100


To purchase PP50 or any other Suregreen permeable pavers please visit our shop section of the website or click here - Suregreen permeable pavers 


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  • SKU: 438079-438352
  • Weight: 1kg-8kg
  • Brands: Suregreen
  • Size: 1m x 10m, 2m x 25m, 2m x 50m, 4m x 11.25m
  • Permeability: 100 l/m2/s