Permeable Paver Design

Permeable paver design is one of the most effective SuDS strategies for reducing runoff, improving infiltration, and delivering attractive, durable surfaces for driveways, paths, and car parks. Whether you’re working on a domestic project or a commercial scheme anywhere in the UK, getting the design right ensures long‑term performance and compliance with planning requirements.

This guide breaks down how permeable pavers work, the key design parameters, and the practical steps needed to build a reliable system.

The CivilWeb Permeable Pavement Design Spreadsheet can save hours of repetitive calculations while ensuring compliance with CIRIA C753 SUDS Manual, reliable accuracy and even optimization tools which can save money on materials during the construction phase.

🌧️ What Permeable Pavers Do and Why They Matter

Permeable pavers allow rainfall to pass through joints or voids in the surface into a free‑draining sub‑base, where water is stored temporarily before infiltrating into the soil or discharging slowly via an underdrain.
They provide:
- Runoff reduction at source
- Improved water quality through filtration
- Groundwater recharge where soils allow
- Compliance with SuDS and planning policy

They’re especially useful on constrained sites where traditional soakaways or attenuation tanks are difficult to install.

🧱 Types of Permeable Paver Systems

System Type	How It Works	Best Applications	Key Considerations
Permeable concrete block paving (PCBP)	Water infiltrates through enlarged joints	Driveways, car parks	Needs regular sweeping to prevent joint clogging
Permeable clay pavers	Similar to PCBP but with clay units	High‑end domestic, heritage sites	More expensive; excellent durability
Plastic cellular grids (filled with gravel or grass)	Water drains through open cells	Overflow parking, low‑traffic areas	Limited load capacity; requires good subgrade
Permeable resin‑bound systems	Water passes through resin‑bound aggregate	Paths, courtyards	Not suitable for heavy vehicles

📐 Key Design Parameters for Permeable Paver Design

1. Site Assessment

Before any calculations, assess:
- Soil infiltration rate
- Groundwater level
- Contamination risk
- Available depth for sub‑base
- Traffic loading

Clay soils may require an underdrain or partial infiltration design.

2. Hydraulic Design

Hydraulic performance depends on:
- Design rainfall (local intensity)
- Void ratio of the sub‑base (typically 30–40%)
- Required storage volume
- Infiltration rate of the subgrade

The sub‑base must be sized to store the design storm, usually a 1:30 or 1:100 event depending on planning requirements.

3. Structural Design

Permeable pavements must support traffic loads while maintaining void space. Structural design considers:
- Sub‑base thickness (often 250–450 mm for cars)
- Aggregate type (open‑graded, angular stone)
- Geotextiles or geogrids for separation and reinforcement
- Freeze–thaw durability

The final design thickness is whichever is greater: hydraulic requirement or structural requirement.

⚠️ Common Risks and How to Avoid Them

Clogging

Sediment accumulation reduces infiltration.
Solution: regular sweeping, edge filters, and good construction controls.

Poor infiltration

Clay soils slow drain‑down.
Solution: add an underdrain or design for partial infiltration.

Settlement or rutting

Occurs when sub‑base is poorly compacted.
Solution: follow manufacturer compaction guidance and use correct aggregate.

Contamination

Avoid permeable systems where runoff contains oils or pollutants unless treatment stages are included.

🛠️ Step‑by‑Step Permeable Paver Design Process

1. Carry out infiltration testing (BRE 365 or equivalent).
   Determine design rainfall and required storage volume.
   3. Select paver type based on traffic and aesthetics.
   4. Size the sub‑base for both structural and hydraulic needs.
   5. Specify geotextiles/geogrids for separation and stability.
   6. Include an underdrain if infiltration is limited.
   7. Prepare a maintenance plan (sweeping, sediment control).
   8. Document SuDS compliance for planning approval.

The CivilWeb Permeable Pavement Design Spreadsheet can be used to complete all the required calculations in accordance with CIRIA C753 SUDS Manual.

🏁 Final Thoughts

Permeable paver design is a robust, attractive, and sustainable drainage solution for UK projects. When designed correctly, it delivers long‑term infiltration, structural stability, and compliance with SuDS requirements. The key is balancing hydraulic storage, structural strength, and maintenance planning from the outset.