Learn about Permeable Paving

Permeable paving consists of solid concrete paving units with joints that create openings in the paved surface when assembled into a pattern. The joints are filled with small stones that allow water to freely enter the surface. The paving units are placed on a bedding layer of small stones that rests over a base and subbase of larger single sized stones. The concrete pavers, bedding and base layers are typically restrained by concrete kerbs. The base and subbase store water and allow it to infiltrate into the soil subgrade underneath the system. Perforated underdrains in the base or subbase could be used to harvest water. Separation geotextiles are often used to separate layers or prevent fines to enter the system from adjacent soils.

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When considering permeable paving, it’s important to understand the principles and follow them correctly. Like most other things in life – if you don’t do it properly, rather don’t do it at all, as you will waste your money.

What is permeable paving?

Permeable paving is when special paving blocks with larger jointing gaps are installed on single size stone base layers in order for water to infiltrate the earth instead of running off the paving.

Why would you install permeable paving?

The local authorities want you to deal with water from your own property and not let it run into the already struggling storm water system.

You might be conscious of using water wisely. Just as you can harvest water from roofs, you can harvest water from pavements.

What is different when comparing permeable paving and conventional paving?

Permeable paving

Conventional paving

Grouting gaps are larger than 6mmGrouting gaps are smaller than 6mm.
Grouted with single sized stone.Grouted with fine sand.
Bedded on single size stone.Bedded on river sand.
Base is constructed with single size stone. (Larger than what was used in the bedding).Base is constructed with a material like G5, that compacts well.
Blocks are 80mm thick in order to have enough rotational interlock with the single size stone grouting.Blocks can be 50 or 60mm thick as sand used for grouting creates enough friction for sufficient rotational interlock.
A sub-base reservoir can be constructed with single size stone, larger than the stone used for the base.A sub-base is rarely installed under the well compacted base.
In certain designs, the soil subgrade isn’t compacted to ensure permeability of the subgrade.The soil subgrade is compacted to the point of refusal.

What are the most common mistakes when it comes to permeable paving?

  • Pavers are grouted with sand and installed on a sand bed. Such a system will clog very quickly.
  • Many “permeable pavers” have design flaws. Having small grouting gaps with bigger holes where the water should flow through simply doesn’t work. Such a system is clogged almost instantaneously. (Bosun made this mistake too, but these products have been discontinued.)
  • 80mm thick pavers are too expensive. In the bigger scheme of things, the pavers are a small part of a permeable system’s cost. It is not about the thickness – it’s about the interlocking capabilities when it comes to stone. (Bosun made this mistake too, but these products have been discontinued.)
  • Geotextiles are used between the bedding and base layers. This is technical, but geotextiles are sediment traps. The secret is in the selection of the right aggregates.
  • Aggregates are not cleaned prior to use. Fine aggregate dust can potentially clog the system. 
  • Construction is not properly supervised.

Does permeable paving actually work?

Without a doubt. There are thousands of examples throughout the world. Permeable pavements are taking preference in more developed countries.

Is it difficult to design a permeable pavement?

If you understand the principles around permeable paving, the design is not difficult. Furthermore, Bosun has design software available that is customised for South African conditions. Click here to learn more – https://www.bosun.co.za/products/paving/permeable-paving/permeable-design-pro/

Benefits of Permeable Paving

Because water is attenuated slower, permeable paving achieves the following:

  • Permeable paving inhibits water flow.
  • Relieves pressure on stormwater drainage systems.
  • Less erosion in drainage channels and streams.
  • Less pollution in natural water resources.
  • Permeable paving creates more development opportunities because less water needs to be attenuated at the cost of developable land.
  • As with any segmented paving, permeable paving could be uplifted and reinstated with ease, providing easy access to underground utilities.
  • As with all segmented paving, permeable paving naturally achieves traffic calming when used on roads.
  • Because fewer and smaller attenuation ponds are required, more land becomes available for development and therefore creates more potential income for property-owners.
  • Attenuation ponds are prone to attract rodents, mosquitos and other pests.
  • Permeable paving offers alternative drainage possibilities in low-slope areas.
  • A permeable paving system could be designed to harvest water.
  • Layer works of permeable paving serve as a natural filter for harvested water.
  • Urban development starves the earth of natural penetrating rainwater. Permeable paving offers a solution to this problem. Instead of water being carried away in stormwater systems, localised penetration of water still take place as intended.
  • As a consequence, underground rivers are fed which generally offer life to agriculture and nature downstream.
  • Permeable paving allows water to slowly drain in a localised area, rather than being flushed away. As a result, it cools down the area in question for a longer time period.
  • Permeable paving is generally available in colours with a lower solar reflectance, which in turn minimises the “Urban Heat Island effect”. Therefore, less energy is consumed by air-conditioning due to a cooler urban environment.

Permeable Paving Design

Design permeable interlocking pavements with Permeable Design Pro (PDP) software. The PDP software application is used to develop permeable aggregate base and subbase thickness solutions for supporting traffic loads, and for water storage and infiltration. PDP now includes rainfall data for 12 major cities in South Africa.

Permeable Design Pro Software

Permeable Paving Design & Construction Guides:

Permeable Paving Installation

There is a growing choice of concrete blocks and flags available from a vast number of manufacturers, designed specifically for permeable paving.

Click below to view permeable paving installation guidelines:

Permeable Paving Maintenance

Like all stormwater control measures, permeable paving requires maintenance as it traps sediment on its surface. Larger particles are initially trapped while allowing water to pass.

Click below to view maintenance guidelines