Are Pavers Considered Permeable?

Are Pervious, Permeable, and Porous Pavers Really the Same?

 

Pervious, permeable and porous pavers (the three P's) are often used by practitioners interchangeably, unaware of their unique characteristics. They're not the same, though.

 

There is a clear and distinct distinction between pavers that are permeable, permeable and porous. Each has some physical and aesthetic qualities that must be considered before designing and building the plan. Careful consideration of site characteristics and project priorities would allow the owner to reduce stormwater runoff and optimize the benefits of water quality offered by these items.

 

The aim of using these forms of pavers to manage stormwater is to restrict the origin runoff, minimize downstream erosion, and improve the quality of water by removing contaminants in the substrata layers. This is partly done in the paver in the case of both pervious and porous pavers before water enters the layers below. Water is circumvented around the paver with permeable pavers, and the filtering process begins in the void space filled with chosen aggregates between the pavers. These three forms require a similar compacted stone aggregate layering system under the ground to absorb the storm water and create a "reservoir" before percolating or piping into the subgrade. Some paver manufacturers refer to this process of stormwater conveyance as the "paver system."

 

While most rainfall events deliver less than 25 mm (1 in.), rainfall intensity is always considered. Less than 25 mm over 15 minutes could cause more issues than 76 mm (3 in.) over 8 hours. Therefore, variances for stormwater runoff management primarily are for high-frequency, low-occurrence events. The water table beneath any of these pavers will rise during a large storm event, preventing rain from being absorbed into the soil. Changes to the Paver system are generally considered when assessing the sub-grade native soil penetration potential and base rock depth for stormwater processing. During the development processes, bioswales, rain gardens, and aquatic structures are also often considered.

 

Permeable Pavers

 

Permeable pavers are used as perfect fits for driveways, walkways, patios and other flat surfaces that require hardscape in both commercial and residential applications.

 

One of the main advantages of permeable pavers is to allow water to pass between the stones (or, in some cases, through them) and back to the surface. This is in lieu of how a concrete slab, for example, directs water to the lowest available point—usually a drain connected to gutters that lead the excess water to the ocean.

 

Basically, permeable paving stones are mounted on top of multiple layers of varying size stone (otherwise known as aggregate) which gradually filter water down into the soil in a manner that will not normally over-saturate it and cause run-off.

 

Types of Permeable Pavers

 

• Turfstone is a unique, eco-friendly option that allows grass to grow right through it. We’ve already gone into detail about the benefits of Turfstone so do have a look if you’re considering it. Keep in mind that plastic is another less costly grass paver. Such grids are also placed on top of aggregate sheets, but the plastic is nowhere near as powerful as Turfstone. Either way, the benefit of these grass pavers is that they promote the growth of grass and ground cover in spaces where it would not normally be possible.

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• Porous concrete pavers and slabs are created through a special concrete mixture (usually with little to no sand and pea gravel) that allows water to flow through the concrete surface to refill groundwater supply gradually.

 

• Interlocking pavers are the most commonly used permeable paver on the market (and include Turfstone). Water flows into the aggregate below through the joints between the rocks. Their strength, considered far superior to poured concrete, is one of the main advantages of interlocking permeable pavers. Because they are bound together, weight is spread all over the surface and because of extreme temperature variations, they are less vulnerable to expansion and contraction.