Porous Pavement Design

Porous pavement design lets stormwater soak where it falls, reducing runoff and meeting UK SuDS planning requirements; choose the right system for your site’s soil, traffic load, and maintenance capacity to ensure long‑term performance.

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 porous pavement does and why it matters

Porous pavement (permeable paving)

Allows rainfall to infiltrate through the surface into a stone reservoir or subgrade, reducing peak flows, improving water quality, and recharging groundwater. It’s a core SuDS technique recommended for source control and urban drainage management.

Main types and where to use them

Type	Typical use	Advantages	Limitations
Porous asphalt	Car parks; access roads	Durable; good for vehicular traffic	Requires specialist laying; sensitive to clogging.
Permeable concrete block paving	Driveways; low‑traffic areas	Modular; easy to repair	Joints can clog; needs correct subbase.
Resin bound/permeable resin	Pedestrian areas; light traffic	Attractive finish; quick drainage	Less suitable for heavy loads; UV/weathering concerns.
Grass/gravel cellular systems	Overflow parking; low use areas	High infiltration; green aesthetic	Limited load capacity; maintenance of vegetation.

Key design parameters (step‑by‑step)

- Site assessment: soil infiltration rate, groundwater depth, contamination risk, and space for a subbase/reservoir. Test infiltration on site before finalising design.

- Hydraulic sizing: Calculate design rainfall and required storage/infiltration volume; use SuDS Manual guidance to size the stone reservoir and overflow.

- Structural design: Match surface type and subbase thickness to traffic loading and frost risk; porous asphalt needs different structural sections than block paving.

- Filtration and maintenance: Include a silt trap, pre‑filter, and routine vacuum sweeping schedule to prevent clogging and loss of permeability.

Common risks, trade‑offs and mitigation

- Clogging from fines and leaf litter reduces infiltration; mitigate with pre‑filters and regular cleaning.

- Contamination risk where runoff contains oils or heavy metals; use treatment stages or avoid porous surfaces in high‑pollution zones.

- Frost heave and settlement if subbase is poorly compacted; follow manufacturer structural guidance and use geotextiles where needed.

Practical tips for UK projects

- Follow the SuDS Manual for planning and maintenance expectations and document infiltration tests and maintenance plans for planning approval.

- Choose materials to match traffic: porous asphalt for heavier use; permeable block or resin for domestic driveways.

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