Understanding the Difference between Permeable and Porous Paving

November 13, 2014

Residential and commercial properties make use of different ways to manage stormwater runoff, among these are porous and permeable paving. These two terms are often used interchangeably by most businesses and clients, but they actually mean different things.

Although they both provide a solution to stormwater management and help increase the aesthetic value of a property, these two have different ways of achieving this.

Permeable Paving

This type of paving consists of a layer of bricks, either concrete or fire clay, on top. Beneath this top layer is another set of layers, sometimes called the ‘paver system,’ consisting of the bedding, base and geotextile membrane. This is where the stormwater is kept until it seeps through the sub-grade.

After hitting the surface of the topmost layer, the stormwater will circumvent the bricks and seep through the void which is filled with aggregates. The filtration of the stormwater only begins in this aggregate-filled void.

Experts note that this type of paving offers less stormwater infiltration compared to porous and pervious paving when it is measured per square meter. So if you will be getting permeable pavement, it is best to get additional pavers to get the same result as porous or pervious paving.

Porous Paving

Like permeable flooring, porous paving has a ‘paver system’ beneath the surface which acts as the reservoir for the stormwater until it seeps through the sub-grade. It too consists of a bedding, base and geotextile membrane. Sometimes it can also have additional layers depending on what it is used for, either for pathways or driveways.

The difference lies in the topmost layer. For porous paving, the top layer is composed of cellular grids filled with sand, dirt or gravel. To keep the aggregates in place, some are applied with resin. This resin would be used to produce a layer of resin bound gravel that will be easier to maintain and handle than loose gravel.

Unlike the previous type of paving discussed, porous paving’s stormwater filtration starts at the surface as holes or spaces in the surface already allow water in. There would be no need for gaps as this topmost layer is 100% porous. This type of paving also allows the ground below to breathe, and tree roots and microbes to interact.

In knowing the difference between these two options, you can fully understand the applications of each and how they work. This will also help you to know which option is best for your property.

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